I made a video before explaining that lasers can heat things to any positive temperature due to the fact that they have a population inversion which gives them a negative absolute temperature which is hotter than any positive temperature. But the problem with that explanation is that a temperature can only be defined in a system that is in thermal equilibrium. So technically you can't assign a laser a negative absolute temperature. Only a "psuedo" negative temperature. But it turns out that explanation isn't necessary since magnetrons can do it and they don't have a negative temperature. Really the best explanation of why a laser can heat things hotter than itself is that you are inputting energy into the system and that energy turns into heat as I explained in this video. All of the mystery fades away when you think of it this way.
So you meant to talk about laser cooling? But you forgot. So now you want to rationalize, what you originally stated in the post made sense? Why can't anybody on YT, just admit they made a mistake? Good luck with your song and dance routine.
@@nc3826 The ratio between atoms in the upper and lower state of the emission of a laser is larger than one. For all temperatures above absolute zero the opposite is always the case (fewer atoms in the upper state), when you plug in a "negative temperature" into the equation for the distribution you get more atoms in the higher-energy state.
Fun fact : this phenomenon is rejected by some climatoskeptics (they think stefan-bolztamnn laws are wrong or misused and that you can't EVER have a colder object emit radiations toward a hotter one) which allow them to say the greenhouse effect isn't a thing (the cold atmosphere can't emit radiations toward the hot ground therefore a rise in CO2 concentration can't lead to an "entrapment" of radiations).
A laser light can not heat something to an infinite temperature but only to a temperature as high as its radiation temperature. Temperature is a property of many things and radiation is one among many. My suggestion is to go to electronics books to understand cuz they would provide you with very physically meaningful examples. Purely classical examples, QM has nothing to do with the problems you have dealing with temperature, not to speak about negative temperature
@@nc3826 I agree he is digging into more nonsense like "a temperature can only be defined in a system that is in thermal equilibrium. " The problems with this video are with the essence of the temperature concept. Its source , the laser, has nothing to do with it. Radiation with the characteristics of laser radiation could originate from something else , ideally it could be extracted even from thermal radiation with a linear, isentropic, filter with laser narrow-band properties. At that point it would have the same temperature of laser radiation. It's interesting, I get all sort of responses from my comments on this video: most readers have problems with the concept of temperature and don't realise that has the dimension of an energy. Even fewer people have put any thought about whom this energy can be attributed to. I believe statistical mechanics is not given enough consideration in school but help might be coming from informatics which deals with very similar concepts but in clearer terms. Something similar is happening with quantum computing, thy are coming up with the most effective QM new didactics.
another interesting thing, for the same reasons that lasers can heat things up beyond the "source temperature" they can ALSO COOL THEM DOWN. yes, cooling lasers. you should do a video on that!
@@GOOGLE-IS-EVIL-EMPIREThey cut both! Or at least made champion bevels on the 2 dm dia. rod. I was waiting for that scrap (most of the 600 lb. rod) to have hit some Elden Ring scale safety device that they were laughing more than they were bruising.
A word of caution. Most ND OD 4 to OD 5 safety glass 1040 to 1060 are great for fiber lasers. However, when the laser strikes the target, it is not just white light that is given off. It is also UV that is not sufficiently protected from your eyes by the safety glasses. Please use caution when viewing the radiated heat signature from molten metal. It can damage your eyes just the same.
I've been a manufacturing laser operator for 14 years and i can attest that the latest fiber lasers are indeed insane. at a mere 6kw you can easily cut through 1 inch steel plate.
When I worked in a condensed matter physics lab, I touched a quartz tube recently heated by an oxy-hydrogen torch. Burned my thumb! Fortunately, it was only superficial.
I did this on accident also, my skin turned white. Luckily it was only a tiny spot and after the blister and new skin you can nearly notice it anymore. The funny thing about the experience for me is I didn't feel it at the second it happened, and the pain just got gradually worse after I realized. It probably got to peak pain about 10 minutes after. The body is strange the way it works. Pretty amazing really.
I was touching red hot pen springs for fun. Quite an experience! No pain, only parallel lines burnt into my fingers, pretty interesting way to modify fingerprints.
I touched a hot plate which was turned on, because i thought it was off. I got near it first to test if its on, didnt feel the heat somehow (maybe it was going on and off and at that moment it was off), and to be sure that its off i touched it. Instantly retracted my hand. This left a white powder on the surface of my hand. Luckily only the very top layer got burned to dust, and the below layers where fine.
Just to make sure everybody’s clear on this, heat flowing from high temperature to low temperature relates to heat _conduction_ between bodies in contact, whereas heating things up with a laser is a case of Radiation Heat Transfer. All pedantistry aside though, great video as usual! Thanks.
@HarmanRobotics, yes, that is 100% true (radiation, rather than conduction, from hot objects to colder objects). In fact, I had intended to modify my comment above to clarify that the laser heating here is Radiation _heating_ but not Radiation Heat *_Transfer_* , as I unwittingly suggested. It would probably be more accurate to characterize it as an energy transformation from radiation to heat. The laser is emitting _stimulated_ radiation - thus the LASER acronym - as opposed to black-body heat radiation. The laser itself is, as he pointed out, not in itself hot.
@@user-sl6gn1ss8p To everyone in this chat, Jesus is calling you today. Come to him, repent from your sins, bear his cross and live the victorious life
Two different proceses: first the IR cameria is simply making an inference between light emission & temperature & its based up on limited IR spectrum, not the full light spectrum. Visible light has a correspondence with much higher temperatures than IR, but the thermal camera does not interprete white light with heat. When you shine a high watt light source on a object that absorbs the light, the light stimulates the electrons in the object causing increase molecular viberations (ie heat).
Sixty Symbols did a video on this topic 11 years ago called "Negative Temperatures are HOT" referring to negative absolute temperatures rather than negative Fahrenheit or Celsius. You can also think of them as beyond infinite temperature. Heat will _always_ move from a negative temperature region into a positive temperature region no matter how hot the positive temperature is. You can literally heat the Sun a minuscule amount by shining a laser at it.
The video feels incomplete, light goes in and the light-matter interaction is where all the black box magic lies, but this video didn't explain that. Would that same laser melt me up like it did the metal? Why or why not? How does the energy of the laser get converted into thermal energy? The material absorbs it, and how much it's absorbed is material-dependent, why? What's the difference between a continuous wave laser and a pulsed laser?
this channel is a lousy science channel and often gets things wrong, so id suggest you look elsewhere. brief answers: yes, the material absorption matters a lot. for cutting metal, CO2 lasers are used because their infrared wavelength is absorbed very efficiently by most metals (even though metals typically reflect most of the visible spectrum), and because they are cheap and easy to scale to huge power levels. even if you try to cut an object that is fairly reflective/transparent to the wavelength, the power of the laser will usually be enough that slightly slower cutting is possible. a bit of reflected power is not harmful to the laser itself, as it will just re-excite the lasing medium, you just need to keep the nozzle cool and carefully choose power levels. continuous lasers are great for cutting and welding as they just deliver lots of raw heat into the material. pulsed lasers are typically used for engraving since they deliver only a very small amount of energy per pulse. the heat they generate is still huge but it only affects the immediate area where the laser hit, as it is already off before the heat can travel far. they can also do different things to materials since their peak output power is orders of magnitude higher. a 40w average pulsed laser can easily be in the megawatts of peak power during the very short pulse. the trick is that they basically use the lasing medium itself as sort of a light capacitor, with the capability of dumping all that energy almost instantly using some clever physics. the bottom line is that CW lasers go deep into the material, while pulsed lasers pretty much only affect the surface. and there are very distinct applications for both.
First, we need to have a basic understand of how heat is transferred. Heat is just thermal energy. You can think of temperature as a potential that drives energy in between two objects. To be correct, it drives heat flux which is in units of energy per units of time. If there is a temperature difference, there will be a heat flux. This is true for the three ways of exchanging heat : conduction (Fourier's law), convection (Newton's law) and radiation (Stefan Boltzmann's law). For convection and convection, this is easy enough to explain as the heat flux is directly proportional to temperature difference. It follows that when the temperatures are equal, there is no heat flux. Because of that, if you want a heat flux, you will need your object's temperature to be lower than the transmitting object's temperature. Imagine that you pump energy into the heater to keep it at a constant temperature, then the heat flux will be proportional to your object's temperature. It also can't go higher than the heater's temperature. This has obvious practical limitations for reaching very high temperatures Radiation is a bit trickier. Stefan Boltzmann's law tells us that the heat flux going out of an object is proportional only to its own temperature. This seems to conflict with what I said earlier but it in fact does not. When you put two objects in an isolated system they will both emit a heat flux. The total heat flux is the difference between the heat fluxes going in between the two objects. So we didn't break anything, the flux is still proportional to the difference in temperatures. But when one flux is negligible in front of the other, we can assume the flux to be unidirectional. Consider two cases : 1) One object's temperature is much higher than the other. Think of the Sun and the Earth. We consider the flux to be only going from the Sun to the Earth. 2) One object barely sees another. Think of a filament light bulb. It sees all of the room and gives it all its energy, but the room barely sees the light bulb. What it will radiate will mostly go back to itself, and just a little will go back to the bulb. Again, we can think of the flow going only from the bulb to the room. These are ways in which heat flows in one direction only using radiation. What's important is that unlike with conduction and convection, the heat flux going into the heated system is independent of its own temperature ! This means that as long as you provide radiation energy, there will be a flux, and your object will keep heating up (until it emits as much as it receives via SB's law). The ways to create radiation I described earlier use the fact that a hot body will emit radiation, but there are other ways, such as using lasers ! Now that we have a deeper understanding of heat transfers, we can answer every question. A real body won't absorb all radiation. It will reflect some, let some pass through and absorb the rest. Obviously, steel is very reflective so you'll need to pump in a lot of energy to heat it up. This means that your hand which is more abortive than steel would probably get vaporized where the laser shines. The properties of a material depend on its atomic structure (it's related to electron energy levels), but in practice we will experimentally determine the absorptivity, reflectivity and transmissivity of a material. Finally, as flux is in units of energy per units of time, a continuous laser will emits its energy continually, whereas a pulse laser in short bursts. These short bursts contain lots of energy and emitting it for longer periods of time is impossible because of how they work : they stockpile energy a for a bit and then release it all instantly. This is why it shoots in pulses, they need time to accumulate energy. Continuous lasers are preferred for cutting because of the heat dissipation properties of a material. Even if you use a high energy pulse, the energy you transferred will get dissipated before you can shoot the second one. Imagine being Sisyphus and pushing the rock very hard for 1 second and then letting it fall for 2, versus pushing it at moderate strength continually.
I agree. Half the video was spent pushing an incorrect assumption as if it were a fact and there was some mysterious paradox going on. And then in couple minutes, blew through several physics concepts with 0 nuance or detail. This was really frustrating to watch.
Also completely ignoring the jet of nitrogen helping that 10kW laser remove the material, because it's not actually vaporising it, mostly just melting. On mild steel, jet of oxygen is often used, to help degrade (cut) the material even faster. Those cuts would be a complete mess without that jet of gas. What author admires so much is not the power to vaporize steel, but separate, clever system for removal of molten steel.
@@solacedagony1234the funny part is this is probably the best educational video I've seen on this channel. It's usually even worse than this from an education standpoint.
Man that laser is so satisfying seeing it cut that thick metal like it's nothing! This is a great approach to heating things up. The way lasers & magnetrons heat things up reminds me of how Tesla considered we could destroy anything if we manipulate the objects frequency in order to vibrate it until it breaks apart. So take that but shift it over to an electromagnetic device that manipulates a large amount of electrical energy and aim it at a focused point and allow the electromagnetic frequencies to interact with that object until it heats it up
One big issue I have with science communication is the oversimplification tends to always fall into epistemic fallacies. When you say things like "This curve is determined by Planck's Law" it implies it has agency or causal power, it conflates our knowledge of the universe with the actual mechanisms. Scientific laws are frameworks for understanding observations, not the "causes" of phenomena. A very common example is when people say a particle knows when it's being observed in a quantum system. Particles don't possess awareness or agency, it's is the act of measuring that interacts with a quantum system. I don't mean to target this directly at The Action Lab, these are just thoughts I've had for some time now.
Nah, you're looking too deep into it. Anyone with basic education understands that it's not the Planck's Law that forces things to emit in a particular way, it's their emission spectrum is distributed according to some law. Also it's appropriate to say exactly as stated in the video, because he was talking about the CURVE, which is a mathematical object described by the Planck's Law. It doesn't exist in reality as well.
That's not what is so bad. The right wants to base American education on a book compiled by illiterate goat herders and the left wants to redefine human gender.
@@drkastenbrot I agree that there are some really annoying examples of people misunderstanding things. But I don't know why it would be fault of Science Communicators - at least if we take the example from Original Comment. At some point you have to "simplify" stuff. After all "science communication" is about taking very complex ideas and making them accessible to "regular" people. Also it's not like some physicists didn't have...similar problems. While I don't think that physicists believed in "electrons having awareness" there were some who leaned too much into "it is important that particle is observed" and giving too narrow meaning to the word "observed". Same with Quantum Entanglement. People see that entangled particles change states faster than speed of light, but then make a big leap to "information is passed faster than the speed of light". And yes some physicists also had issues here. I do agree that there are bad science communicators or people who "explain things" in bad faith. Or worse, scientists that start to believe in something and this makes them biased. The worst are scammers of course - though usually not physicists (there are couple, but you probably know about them). I mean I saw explanation of how "healing energy of the crystals" can be explained by quantum entanglement and "observation theory" 🤮. But I don't think Action Lab nor most science communicators on You Tube are guilty of this. At least the ones I'm watching. They simplify - sure. But if small part of the audience takes something to mean something that science communicator didn't originally mean, Science Communicator can only be partially responsible. Especially if we mean people like those who will understand "This curve is determined by Planck's Law" as "It is Planck's Law that makes objects radiate/absorb energy". It's along the lines of "If Newton didn't 'discover' gravity, we could jump infinitely high". And yes, it would be better if "determined" was replaced by "described". But then there will be a subset of people who will still think it's somehow the law that makes it happen. Even if you produced absolutely flawlessly 100% accurate video with accurate wording - you will still have people misunderstanding it. It's just that the video will now be much less accessible to regular viewer. Science Communicators have to find balance between accuracy, complexity and accessibility. And I think that Action Lab manages to do it.
I study chemistry in my masters now. We learn a lot about the interaction between light and matter. The idea, that light is just a mediator between matter blew my mind. It's like the tone that we make in order to communicate. You can change pitch (frequency) and decibel (amplitude) to form understandable words. Light is matter communicating with uts surrounding. Check boson-fermion interaction. And that light has no temperature is also freaky af. Thanks for the video!
this makes a lot of sense. I've always felt that the designation of lasers as "negative temperature" was just a lazy way to make the math work for something we didn't understand, but it being a nonthermal source makers much more sense than a negative temperature source. Then its designated as a negative temperature source because heat will always move away from a negative temperature source. I can think of it practically like the relationship between being pushed by an object vs being acted on by gravity. the object pushing you has a finite amount of energy that it can transfer and so you will only move at a certain maximum speed (like a normal thermal source), but if you have no thing under you and no air resistance gravity could theoretically speed you up infinitely as its a constant source of energy (like a laser). I know I'm saying anything profound but its nice to finally learn this. My wife jokes with me all the time by reminding me of "negative temperature" because I would get so heated about it.
The laser light is transferring energy. Whatever the laser is shining on is accumulating that energy so it is a question of time and energy not simply energy.
Well to be fair... Whatever gave the laser that energy also lost it at some point, so there is an energy equilibrium, but the system is probably on the scale of the earth. It becomes the universe if you use any elements greater than iron, like uranium in nuclear reactors. But at that point it would be mass-energy equilibrium ?
7:34 doesn't that mean you can heat an object more assuming you focus all of it on a smaller object since a smaller object won't radiate the heat as fast right?
Technically no, but practically yes. Thermal emissivity is based on material and chemical properties, not physical dimensions, so a target of a certain material is always going to radiate energy at the same rate, regardless of size. While that's the technical correct answer, the practical answer depends on a lot of factors and that complicated math soup will usually result in a smaller target heating up more quickly and staying at a higher temperature than a larger target. Which would not be the case if you somehow conducted this test in scientifically ideal and perfect conditions. Imagine that your targets are two cups, a small one and a large one. If you pour water into both of them at the same rate, the small one will obviously fill first, because it is smaller. Once it fills, the water starts pouring out over the edge; that's the thermal emission, radiating the "heat" away at the same rate at which it is being delivered. Once the large cup is filled, it too will start spilling over the edge and the amount of water spilling over will be the same as the amount spilling from the smaller cup because they both have the same amount flowing in.
@@boeubanks7507 iirc it's 100 or so lasers (don't quote me on that) but they are amplified SO MUCH that for the brief moment where it hits the capsule, it's probably the highest power (W) thing in the universe.
@mismis3153 Thank you for making my point. Also, I would be careful saying it is the highest wattage thing in the universe. That is a bold statement, cotton, when you have things like magnatars, pulsars, neutron stars, and black hole jets out there. If you want to say on this planet, I could go with that though.
5:55 I'm not sure that this is the whole story. If it were, then any monochromatic light source would do the trick, but if you let two otherwise isolated systems exchange heat via radiation through a monochromatic filter they'd still get to thermal equilibrium. In that case the relation between frequency and intensity (in connection with emission/absorption coefficients) would ensure that. Also what is the "temperature" of a laser, where the light emitting atoms are "pumped" into an inverted state that isn't something that corresponds to a thermal equilibrium (AFAIK that inversion would correspond to a "negative temperature", one would characterize with beta=1/T in the statistical description to get continuously from non-inverted to inverted states).
This is a great video, I design laser engraving systems. We go down to spots with a size of a few microns to get some enormous power density. This is a great basic video explaining some of the phenomenon
I learned yesterday that we figured out what was diamonds were by vaporizing them, and then doing experiments to see what the gas was! This was in the 1700s! One of the methods they used was simply lenses. How crazy is that. I've seen people burn rocks, but diamonds just using the sun is crazy to me. He should do this himself. Makes me appreciate glass. Where would science be without it. They used glass lenses to vaporize diamond to capture the gas in glass vessels to weigh the gas! Then used glass beakers to do the tests.
In a Thought Emporium video about "cold fire" they explained that thermal temperature is different from "electron temperature" is it possible these are related?
Did you say that you cannot focus sunlight to a pinpoint that is hotter than the source? If I have a very large surface at 1000 C, and I focus the light (IR) to a pinpoint, the pinpoint will not be hotter than 1000 C?
@@DANGJOS You don't help anyone by just repeating the statement. The Stefan-Boltzmann Law works with an area, the magnification(in one direction) has an effect for the equilibrium of the heat transfer.
What happens if you get like a spherical array of those laser cutters or even stronger lasers, pointed them all inwards towards the direct centre of the sphere and then fire them at something in that centre point?
It'll likely vaporize quite rapidly. It's basically a lower power version of one of the proposed methods of igniting fusion. Fuel is inserted into a pellet and it gets hit with high power lasers from multiple directions; the blast wave of the shell vaporizing compresses the fuel to fusion conditions.
5:27 Question: how does LASER compare to SOLAR radiation? I think of the sun as emitting all manner of spectrum, based on something somebody said about Parker space probe data result ... What is the EM difference of focused LASER vs solar, thinking a minuscule Earth sized critter is in a straight line to the solar radiance, thus reasonably coherent beams of photons??? Just wondering 'bout Black Body radiation vs EM ... the rest was very educational, but caused me this question about exceeding limits. If a lens focused a particular wavelength, continually powered by the sun, how would the physical interaction effect result differently, laser vs specific solar radiation? (if the lens were focused in outer space without pesky atmospheric light scattering annoyance 😬) EDIT: I will search "what happens if you focus a laser Action Lab" based upon a comment.
For this you have to understand lasers, which this video doesnt actually explain at all. The key takeaway is 0:49 "Light doesn't have temperature". When sun shines on you, it is a thermal exchange. Radiation is what carries that exchange. Laser is not thermal exchange, when laser device shines on you it doesnt exchange heat with you thermally. Laser is the heat itself, which is produced differently than the blackbody radiation. Laser is magic that follows very exotic principles that are much more advanced than the widely known 2nd law of thermodynamics. Laser is not a spectrum of light, laser is one specific wavelength. If you filter out a portion of the light spectrum, you will also reduce the heat transferred to you, as filter will absorb heat from filtered wavelengths. Thats how wine bottles work, they absorb part of the light to protect the wine. Tinted windows and sunglasses are filters too, but instead of filtering out a color, they pass through only certain orientation of lightwaves, absorbing the rest (thats why tinted windows make cars colder than no tint).
I used to run one of those LT8 laser cutters for various metal tubing. Thay really are amazing, and SUPER high tech. There are dozens of mirrors that the lazer bounces off before it goes through the lense (which is like a $350-500 lense). And thats not including the tube feeding and sensing system which I think is even more complex.
Laser dust, aka metal dust. The exhaust is drawn into an air handler. If you want mars soil, ask for some laser dust. It's nearly the same density of air. Gets everywhere. Probably giving me Parkinson's in a few years.
@@skydyverjym our mazak and LVD lawyers draw the dust in a one foot tube. The collector is much larger. The dust falls out of the air when the air velocity slows. There are large filters in the top and then more filters before the air goes back into the shop. Underneath are two 50 gallon drums to collect the dust. One fills first allowing it to get emptied without shutting down the laser. Changed/ dumped weekly.
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You can heat metallic things with "radio wave" frequencies using induction furnace...
If the detector goes off for an infrared laser, it's too late. Either you actively have a firearm pointed at you, or there are hot laser guided munitions on its way to your location. It won't be much help at all, other than warning you of the inevitable.
so if you use mirrors and multiple magnifying glasses to focus sunlight from multiple directions on the same spot, you can heat the point up higher than the surface of the sun right? because then you can also put as much energy into one point as you want.
3:13 OK, this is messing with my mind... Laser at 30° angle(for arguments sake), round bar spinning, you'd expect the laser to cut a cone on the end of the bar, but the finished cross-section is a square?
There are sparks coming out of the middle while the laser is cutting. I'm gonna say it's cutting a pipe and not a solid steel rod. It's slightly cone shaped, but that would be a bevel on the outer pipe wall.
Here is a question: Can we use fiber optic cables to carry the focused sunlight(maybe with multiple lenses) to somewhere else and direct all the light onto a single point. Can we achieve a higher temperature?
You can definitely make something hotter than the surface of the sun with just sunlight, you just need to focus the light to a smaller point. The problem is that any material vaporizes before it even reaches that temperature.
No, he's not wrong about that. You can definitely get a higher temperature by focusing to a smaller spot but you cannot get a temperature hotter than the source. For the Sun that maximum temperature is just under 10,000 F; in practice you can expect about 5,000 F, few materials can withstand that.
@@HarmanRobotics evidently this argument has been going on on the internet for a while. Charge your laser with a solar panel and then nuke the crap out of what ever you want. QED.
@@HarmanRobotics Getting something hotter than the surface of the sun is practically impossible due to how little of its energy actually reaches Earth and because you'd have to have a magical way to input energy without losing much to the environment. With that said, there's nothing in the physics theory that dictates that it's impossible to use sunlight to heat something up hotter than the sun itself. All you need is a way to get the energy from the sunlight into something that won't lose that energy due to radiation and conduction once it's heated up. This video mixed up 3 concepts that have nothing to do with each other. The line about sunlight is that you can't use a magnifier to focus more energy into a spot than what already reaches the magnifier itself. The limitation of temperature only applies to conduction and convection processes in matter. Outside of that, electromagnetic waves could theoretically inject energy into a system indefinitely and literally heat it up to infinity.
2nd law has to deal with entropy NOT temperature, and it refers to an "isolated system". Temperature is a simple interpretation of entropy moving from hot sources to cold. What's your total system in the 10kW laser example?
Does this mean that if you had to point the weaker laser at a sheet of metal for a long time it would end up getting red hot. ( Ignoring the fact that the atmosphere will most likely cool it down at a quicker rate. )
I kinda like seeing how this channel went from the clickbaity hydraulic press and vacuum chamber videos to thermodynamics, heat transfer and blackbody radiation, even it's on a rudimentary level, this is still very informative and interesting !
That's a 10KW Trumpf (note the 'f' at the end) laser cutter. I use to work with a 4KW unit, of the same make, years ago. Those particular units are used to cut metal. Steel, most often. It can cut finer, and more accurately, than a plasma cutter. Though the plasma cutter is about 1/10th the cost.
Then you should also know that these lasers are not vaporising, but mostly just melting the steel and its the jet of gas that makes it "disappear". That's very important feature. We couldn't cut steel without it.
The closest invention to my emf kite is a cathode ray tube. Which does push but I’m curious to see if you can get push with open electricity and no vacuum
What if laser is not a heat energy, but a motion energy? Ok i may a little bit confuse but just imagine like starting fire from two wood by friction ? Does it the same or different?
As a child in the 70s, I was fascinated by lasers. I remember how outrageously expensive the first laser pointers were. In Japan (or China? Sorry, don't know exactly), branches are removed from the tops of trees by laser. It looks very impressive. Lasers are simply cool (and hot). :-Þ
Even though the laser and microwave can heat objects and increase the temp above the input power, it has a continuous input of power to replace the power emitted. It is not measured in the same way as a thermal source emitting energy, as the laser and microwave has power being added to it as it expends the power.
Great observation! Before use, the phosphor has to be charged with visible light (e.g. sunlight), so that, when hit by infrared light, it releases the energy stored during the charging process
A laser differs from a regular light in the fact that it is monocromatic, coherent, and directional.. so, how can a laser be able to heat something to infinity while a concentrated regular light only can heat something up till it gets to the temperature of the source of that light?? What is the difference in the business end of the light, when impacts a surface?... I wonder..
This is exactly my question. The video didn't really explain why laser light is different. Perhaps the coherence of the light is the big difference here? You could surely filter out all the frequencies of sunlight to a single frequency, and concentrate it.... but you couldn't make it coherent.
@@stevesether It kept me thinking, could it be that "light transferring energy" behave as heat or electric current?, where you have "temperature" and "heat" or "voltage" and "current" respectively.. let's say.. an impulsory force and an ammount of energy being transfered.. once the force is in equilibrium you can't "push" anymore energy to the other side... Laser might have, or be able to get, an arbitrarily high level of "force" to "push" while for sunlight or any random white light the "force" is only as strong as for the source of that light, so it cannot achieve higher temperatures. In such a case, what would be the "voltage" (or pressure making a fluids analogy) for the light? I don't know..
I think he misstates the science. It is in fact possible to used concentrated light from the sun to exceed the temperature of the surface of the Sun. The Odeillo solar furnace in France achieved a temperature of 10,000 C. According to what I read, there's no upper limit on the temperatures that can be achieved. EDIT: this paragraph is wrong! See follow-up below. What you cannot do is focus the Sun's light down to a single point, because the Sun's light is disk shaped as viewed on Earth, so even at perfect focus, you always get a disk.
what about the entropy of the laser's light. doesnt it would theoretically be a maximum threshold to how hot we can heat up something and not just the energy output of the laser?
Potentially. Something in the infrared range like 900ish nm, doesn't make you feel hot, but it heats up tissue inside since it penetrates the body and you can end up damaging your eyes. The sun is blasting you with broad spectrum infrared which is good for you but the eyes are very sensitive which is why you don't look straight at the sun.
I think the rough answer is that the kinetic energy of the particles goes up faster than the speed. This is because the relativistic mass of the particles goes up with their speed. To reach the speed of light the particles would need to be infinitely heavy - which never happens. In a sense the energy creates extra mass. E = mc^2 comes in here somewhere, I think my explanation is basically correct, but probably no use the latest way of explaining it.
The kinetic energy of a (massive) particle moving at the speed of light is infinite, which would correspond to something like 'infinite temperature'. No matter how much energy you put into an object, you can't make it go equal to (or faster than) the speed of light.
At first, I thought the temperature of an object couldn’t exceed the temperature of the source, but lasers just proved me wrong! This is insane, I have to try it!
Well, lasers have a population inversion in the internals of the laser. So if you had to define a temperature for the laser it would be a negative absolute temperature which is hotter than any positive temperature. But the problem is that in order to define a temperature the system has to be in thermal equilibrium, and that is not the case with lasers. So, although it can be explained by the fact that they have a negative temperature, I think that this explanation is more correct.
Now, what about total reflection, like in glass/air interface under specific angle ? It does not depend on conductivity, so it should not decrease... Would probably require a glass block and heating it evenly would be even more changing
2nd law of thermodynamics is about entropy change in close system. It means heat flow from hot to cold in the case of conduction. In the case of laser, it involves electrical energy input, excitation, spontaneous emissions, stimulated emissions. Each step is govt by thermo law. Kind of like an engine cycle.
Atoms and molecules can absorb energy from electomagnetic waves because they are made from charge particles (electrons and protons). The oscillating electromagnetic field in the waves makes the electrons in the material wobble around a lot, which cause the atoms/molecules wobble around a lot too. This gives the molecules kinetic energy and thus heats them up. The specifics of how this happens is a bit complicated (look up "dielectric heating" and "electric dipole moment" for more info) but that is the gist of it.
@Aphobis I imagine molecules talking to each other. Hey Bob, that isn't a lazer beam is it? Kevin; 'It is! We're totally effed!' Bob; 'I'm shaking like a leaf over here!' [POP!] Bill; 'There goes Bob. Straight to vapor! The poor b@s+Rd didn't have a chance.' Kevin; 'You're next Ronny!'
What if you put the sun inside the laser stick and focus it's entire energy to a single spot? Can't it still get hotter than the sun itself? Because like the battery source or the electricity flowing in the magnetron also the sun has an active energy source with fusion.
It was cool seeing those Trumpf lasers. I used to work on Trumpf lasers, anywhere from 8kw to 24kw. I mainly operated a 24kw laser paired with a 3060 gantry. It was the first 3060 in the United States to have a 24kw resonator paired with it. I would do all kinds of stuff, from really thin aluminum, to 2 inch thick steel. I knew all the little tricks and techniques to get that thing to cut any material with no laser burr too. The science involved is quite complicated.
well as it is emitting energy, and that energy is usually measured over an area not a point, so you can concentrate that energy by reducing the area that it is dissipating energy over. so yes you can focus a collimated beam of light and make it higher powered.
@@johng.1703 but you can't go on forever concentrating and at some point you are re-radiating all the power you are concentrating since radiation goes with the 4th power of temperature. I might not understand what you want to demonstrate though
I work for a company that makes kW class cutting lasers. And I can tell you that the dust that comes from cutting metal is a pain to deal with. It's incredibly fine since it is condensed metal, essentially a percipitated fog of tiny particles.
does all of the suns radiation come from it's temperature or are some of the photons directly created by the fusion reaction. similar to a laser that would mean you could get something hotter than the sun.
Theoretically it could get as hot as plack temperature, where the wavelength of the thermal radiation reaches the planck length. So about 1.416 x 10^32 Kelvin. That is as hot as anything can get.
question , If a laser runs for say 1 hour just pointed at nothing , say out to space , and you measure the lasers head body cavity temperature , Then under the same conditions , but , this time the laser is being used to say , cut metal , Would we measure the lasers body , or head, or cavity etc.. to be hotter ? In other words does a laser get hotter if its doing work ? has a load on it , compared to no load . Thank you very much.
Once the light is emitted from the laser, it does not interact with it anymore, whether it ends up hitting metal or nothing, the laser has no "idea" what happened to it because the information does not come back. One exception would be if some light is reflected off the metal and comes back to hit the laser, heating it up, but considering your question I think this is a technicality
if i can see the infrarred in the dark plate of the radiometer, ¿can y build a sensor black plate to watch the iifrared light by putting it into a transparent box in vacumn? sorry for my bad english, saludos desde argentina
LED flashlights sort of do this since they emulate a black body source. Used to have one of those Nitecore lights and with great difficulty it could get to charring and smoldering paper.
37 years ago I earned an Associates in Laser Electro-Optics Technology. That 2 year degree kicked in the door for a long career. I ended up installing, repairing x-ray equipment. I earned my degree 37 years too early.
So if I understand it correctly. The laser just turns the light energy into heat energy at the point of impact. The total energy of the light energy will be more than the energy required to heat up the material by X amount. other will be lost in form of reflected light or other forms of energy. You literally said it. light has no temperature. so no paradox?
the laser just delivers energy, like any source of EM radiation. the material absorbs some of it, heating up. as it heats up it also radiates back that energy as thermal radiation, eventually reaching equilibrium when it radiates the same amount you put in. the maximum temperature you can reach is then limited by how tight you can focus that radiation, and thats where lasers are very special.
I made a video before explaining that lasers can heat things to any positive temperature due to the fact that they have a population inversion which gives them a negative absolute temperature which is hotter than any positive temperature. But the problem with that explanation is that a temperature can only be defined in a system that is in thermal equilibrium. So technically you can't assign a laser a negative absolute temperature. Only a "psuedo" negative temperature. But it turns out that explanation isn't necessary since magnetrons can do it and they don't have a negative temperature. Really the best explanation of why a laser can heat things hotter than itself is that you are inputting energy into the system and that energy turns into heat as I explained in this video. All of the mystery fades away when you think of it this way.
So you meant to talk about laser cooling? But you forgot. So now you want to rationalize, what you originally stated in the post made sense?
Why can't anybody on YT, just admit they made a mistake? Good luck with your song and dance routine.
@@nc3826 The ratio between atoms in the upper and lower state of the emission of a laser is larger than one. For all temperatures above absolute zero the opposite is always the case (fewer atoms in the upper state), when you plug in a "negative temperature" into the equation for the distribution you get more atoms in the higher-energy state.
Fun fact : this phenomenon is rejected by some climatoskeptics (they think stefan-bolztamnn laws are wrong or misused and that you can't EVER have a colder object emit radiations toward a hotter one) which allow them to say the greenhouse effect isn't a thing (the cold atmosphere can't emit radiations toward the hot ground therefore a rise in CO2 concentration can't lead to an "entrapment" of radiations).
A laser light can not heat something to an infinite temperature but only to a temperature as high as its radiation temperature. Temperature is a property of many things and radiation is one among many. My suggestion is to go to electronics books to understand cuz they would provide you with very physically meaningful examples. Purely classical examples, QM has nothing to do with the problems you have dealing with temperature, not to speak about negative temperature
@@nc3826 I agree he is digging into more nonsense like "a temperature can only be defined in a system that is in thermal equilibrium. " The problems with this video are with the essence of the temperature concept. Its source , the laser, has nothing to do with it. Radiation with the characteristics of laser radiation could originate from something else , ideally it could be extracted even from thermal radiation with a linear, isentropic, filter with laser narrow-band properties. At that point it would have the same temperature of laser radiation. It's interesting, I get all sort of responses from my comments on this video: most readers have problems with the concept of temperature and don't realise that has the dimension of an energy. Even fewer people have put any thought about whom this energy can be attributed to. I believe statistical mechanics is not given enough consideration in school but help might be coming from informatics which deals with very similar concepts but in clearer terms. Something similar is happening with quantum computing, thy are coming up with the most effective QM new didactics.
another interesting thing, for the same reasons that lasers can heat things up beyond the "source temperature" they can ALSO COOL THEM DOWN. yes, cooling lasers. you should do a video on that!
Also, he cut pipes. I want to see video about lasercut in dot, in deep metal block.
Sorry laser cooling has numerous TH-cam videos already.... Just this one wasn't one of them....Since he forgot to include that part....
Finally, lasers are cool. It probably took some nerds in the '70s ions to do this I bet.
@@GOOGLE-IS-EVIL-EMPIREThey cut both! Or at least made champion bevels on the 2 dm dia. rod. I was waiting for that scrap (most of the 600 lb. rod) to have hit some Elden Ring scale safety device that they were laughing more than they were bruising.
@@nc3826forgot? It wasn't the focus of the presentation.
"Imagine if we shine ten million of them in the same spot". For some reason I was expecting an xkcd collab after that.
Lmao me too
YH. That would be something
Didn't they just do one about shining lots of lasers on the moon?
you would be disappointed , they couldn't be coherently added, different directions, different degrees of freedom.
"What if we tried more power?"
A word of caution. Most ND OD 4 to OD 5 safety glass 1040 to 1060 are great for fiber lasers. However, when the laser strikes the target, it is not just white light that is given off. It is also UV that is not sufficiently protected from your eyes by the safety glasses. Please use caution when viewing the radiated heat signature from molten metal. It can damage your eyes just the same.
I've been a manufacturing laser operator for 14 years and i can attest that the latest fiber lasers are indeed insane. at a mere 6kw you can easily cut through 1 inch steel plate.
Evidently at 400 yottawatts, (YW) you can very thoroughly cook a planet. lol
What is underneath the plate? Rocks?
@@censoredeveryday3320 no, the machine has a table bed made of steel. the lasers output is tuned to only cut the workpiece
@censoredeveryday3320 usually just a gap of space and heat resistant blocks or something underneath.
@@adamreside3912 most machines just use thick steel plates as heat barriers
I Accidentally put my hand on some 800C Steel while using an oxyacetylene torch one. Sizzled like your 'assistant'
Been there. My fingers have additional contours
When I worked in a condensed matter physics lab, I touched a quartz tube recently heated by an oxy-hydrogen torch. Burned my thumb! Fortunately, it was only superficial.
I did this on accident also, my skin turned white. Luckily it was only a tiny spot and after the blister and new skin you can nearly notice it anymore. The funny thing about the experience for me is I didn't feel it at the second it happened, and the pain just got gradually worse after I realized. It probably got to peak pain about 10 minutes after. The body is strange the way it works. Pretty amazing really.
I was touching red hot pen springs for fun. Quite an experience! No pain, only parallel lines burnt into my fingers, pretty interesting way to modify fingerprints.
I touched a hot plate which was turned on, because i thought it was off.
I got near it first to test if its on, didnt feel the heat somehow (maybe it was going on and off and at that moment it was off), and to be sure that its off i touched it. Instantly retracted my hand.
This left a white powder on the surface of my hand. Luckily only the very top layer got burned to dust, and the below layers where fine.
Just to make sure everybody’s clear on this, heat flowing from high temperature to low temperature relates to heat _conduction_ between bodies in contact, whereas heating things up with a laser is a case of Radiation Heat Transfer.
All pedantistry aside though, great video as usual! Thanks.
Heat will also flow from something hotter to something cooler via radiation, not only conduction.
@HarmanRobotics, yes, that is 100% true (radiation, rather than conduction, from hot objects to colder objects). In fact, I had intended to modify my comment above to clarify that the laser heating here is Radiation _heating_ but not Radiation Heat *_Transfer_* , as I unwittingly suggested.
It would probably be more accurate to characterize it as an energy transformation from radiation to heat. The laser is emitting _stimulated_ radiation - thus the LASER acronym - as opposed to black-body heat radiation. The laser itself is, as he pointed out, not in itself hot.
2:21 it made the PEW PEW noise!!!
A powerful PEW at that
I cant believe the laser sounds in movie were accurate all along
@@user-sl6gn1ss8p
To everyone in this chat, Jesus is calling you today. Come to him, repent from your sins, bear his cross and live the victorious life
@@hortusdeescapismo its not the laser, its the impact that makes the sound
Two different proceses: first the IR cameria is simply making an inference between light emission & temperature & its based up on limited IR spectrum, not the full light spectrum. Visible light has a correspondence with much higher temperatures than IR, but the thermal camera does not interprete white light with heat.
When you shine a high watt light source on a object that absorbs the light, the light stimulates the electrons in the object causing increase molecular viberations (ie heat).
Sixty Symbols did a video on this topic 11 years ago called "Negative Temperatures are HOT" referring to negative absolute temperatures rather than negative Fahrenheit or Celsius. You can also think of them as beyond infinite temperature. Heat will _always_ move from a negative temperature region into a positive temperature region no matter how hot the positive temperature is. You can literally heat the Sun a minuscule amount by shining a laser at it.
Yes! The Action Lab also has a video on this
@@DANGJOSwhich video?
@@blueslime5855 If you search "what happens if you focus a laser Action Lab" you should find it
I'm outside using a standard laser pointer but I'm trying my best to help make winter just a little more mild this time. You're welcome guys!
@@FlameMage2 This winter has been super mild here in Texas. Keep up the good work!
LASER = Light Amplification by Stimulated Emission of Radiation 🙂
Radiation really is 🤩 .
yes this sums up the whole video actually
@@BibhatsuKuiri thats what im trying to say.
GIF.
Stimulated 😍😍
The video feels incomplete, light goes in and the light-matter interaction is where all the black box magic lies, but this video didn't explain that. Would that same laser melt me up like it did the metal? Why or why not? How does the energy of the laser get converted into thermal energy? The material absorbs it, and how much it's absorbed is material-dependent, why? What's the difference between a continuous wave laser and a pulsed laser?
this channel is a lousy science channel and often gets things wrong, so id suggest you look elsewhere. brief answers: yes, the material absorption matters a lot. for cutting metal, CO2 lasers are used because their infrared wavelength is absorbed very efficiently by most metals (even though metals typically reflect most of the visible spectrum), and because they are cheap and easy to scale to huge power levels.
even if you try to cut an object that is fairly reflective/transparent to the wavelength, the power of the laser will usually be enough that slightly slower cutting is possible. a bit of reflected power is not harmful to the laser itself, as it will just re-excite the lasing medium, you just need to keep the nozzle cool and carefully choose power levels.
continuous lasers are great for cutting and welding as they just deliver lots of raw heat into the material. pulsed lasers are typically used for engraving since they deliver only a very small amount of energy per pulse. the heat they generate is still huge but it only affects the immediate area where the laser hit, as it is already off before the heat can travel far. they can also do different things to materials since their peak output power is orders of magnitude higher. a 40w average pulsed laser can easily be in the megawatts of peak power during the very short pulse. the trick is that they basically use the lasing medium itself as sort of a light capacitor, with the capability of dumping all that energy almost instantly using some clever physics. the bottom line is that CW lasers go deep into the material, while pulsed lasers pretty much only affect the surface. and there are very distinct applications for both.
First, we need to have a basic understand of how heat is transferred. Heat is just thermal energy.
You can think of temperature as a potential that drives energy in between two objects. To be correct, it drives heat flux which is in units of energy per units of time. If there is a temperature difference, there will be a heat flux. This is true for the three ways of exchanging heat : conduction (Fourier's law), convection (Newton's law) and radiation (Stefan Boltzmann's law).
For convection and convection, this is easy enough to explain as the heat flux is directly proportional to temperature difference. It follows that when the temperatures are equal, there is no heat flux. Because of that, if you want a heat flux, you will need your object's temperature to be lower than the transmitting object's temperature. Imagine that you pump energy into the heater to keep it at a constant temperature, then the heat flux will be proportional to your object's temperature. It also can't go higher than the heater's temperature. This has obvious practical limitations for reaching very high temperatures
Radiation is a bit trickier. Stefan Boltzmann's law tells us that the heat flux going out of an object is proportional only to its own temperature. This seems to conflict with what I said earlier but it in fact does not. When you put two objects in an isolated system they will both emit a heat flux. The total heat flux is the difference between the heat fluxes going in between the two objects. So we didn't break anything, the flux is still proportional to the difference in temperatures.
But when one flux is negligible in front of the other, we can assume the flux to be unidirectional. Consider two cases :
1) One object's temperature is much higher than the other. Think of the Sun and the Earth. We consider the flux to be only going from the Sun to the Earth.
2) One object barely sees another. Think of a filament light bulb. It sees all of the room and gives it all its energy, but the room barely sees the light bulb. What it will radiate will mostly go back to itself, and just a little will go back to the bulb. Again, we can think of the flow going only from the bulb to the room.
These are ways in which heat flows in one direction only using radiation. What's important is that unlike with conduction and convection, the heat flux going into the heated system is independent of its own temperature ! This means that as long as you provide radiation energy, there will be a flux, and your object will keep heating up (until it emits as much as it receives via SB's law). The ways to create radiation I described earlier use the fact that a hot body will emit radiation, but there are other ways, such as using lasers !
Now that we have a deeper understanding of heat transfers, we can answer every question. A real body won't absorb all radiation. It will reflect some, let some pass through and absorb the rest. Obviously, steel is very reflective so you'll need to pump in a lot of energy to heat it up. This means that your hand which is more abortive than steel would probably get vaporized where the laser shines.
The properties of a material depend on its atomic structure (it's related to electron energy levels), but in practice we will experimentally determine the absorptivity, reflectivity and transmissivity of a material.
Finally, as flux is in units of energy per units of time, a continuous laser will emits its energy continually, whereas a pulse laser in short bursts. These short bursts contain lots of energy and emitting it for longer periods of time is impossible because of how they work : they stockpile energy a for a bit and then release it all instantly. This is why it shoots in pulses, they need time to accumulate energy. Continuous lasers are preferred for cutting because of the heat dissipation properties of a material. Even if you use a high energy pulse, the energy you transferred will get dissipated before you can shoot the second one. Imagine being Sisyphus and pushing the rock very hard for 1 second and then letting it fall for 2, versus pushing it at moderate strength continually.
I agree. Half the video was spent pushing an incorrect assumption as if it were a fact and there was some mysterious paradox going on. And then in couple minutes, blew through several physics concepts with 0 nuance or detail. This was really frustrating to watch.
Also completely ignoring the jet of nitrogen helping that 10kW laser remove the material, because it's not actually vaporising it, mostly just melting. On mild steel, jet of oxygen is often used, to help degrade (cut) the material even faster. Those cuts would be a complete mess without that jet of gas. What author admires so much is not the power to vaporize steel, but separate, clever system for removal of molten steel.
@@solacedagony1234the funny part is this is probably the best educational video I've seen on this channel. It's usually even worse than this from an education standpoint.
Man that laser is so satisfying seeing it cut that thick metal like it's nothing! This is a great approach to heating things up. The way lasers & magnetrons heat things up reminds me of how Tesla considered we could destroy anything if we manipulate the objects frequency in order to vibrate it until it breaks apart. So take that but shift it over to an electromagnetic device that manipulates a large amount of electrical energy and aim it at a focused point and allow the electromagnetic frequencies to interact with that object until it heats it up
One big issue I have with science communication is the oversimplification tends to always fall into epistemic fallacies. When you say things like "This curve is determined by Planck's Law" it implies it has agency or causal power, it conflates our knowledge of the universe with the actual mechanisms. Scientific laws are frameworks for understanding observations, not the "causes" of phenomena. A very common example is when people say a particle knows when it's being observed in a quantum system. Particles don't possess awareness or agency, it's is the act of measuring that interacts with a quantum system.
I don't mean to target this directly at The Action Lab, these are just thoughts I've had for some time now.
Nah, you're looking too deep into it. Anyone with basic education understands that it's not the Planck's Law that forces things to emit in a particular way, it's their emission spectrum is distributed according to some law. Also it's appropriate to say exactly as stated in the video, because he was talking about the CURVE, which is a mathematical object described by the Planck's Law. It doesn't exist in reality as well.
@@arseniixmost people with basic education dont know ABOUT planck's law
That's not what is so bad. The right wants to base American education on a book compiled by illiterate goat herders and the left wants to redefine human gender.
one of the worst ones is quantum entanglement, where lots of people believe that there is some sort of communication between the particles
@@drkastenbrot I agree that there are some really annoying examples of people misunderstanding things. But I don't know why it would be fault of Science Communicators - at least if we take the example from Original Comment. At some point you have to "simplify" stuff. After all "science communication" is about taking very complex ideas and making them accessible to "regular" people. Also it's not like some physicists didn't have...similar problems. While I don't think that physicists believed in "electrons having awareness" there were some who leaned too much into "it is important that particle is observed" and giving too narrow meaning to the word "observed". Same with Quantum Entanglement. People see that entangled particles change states faster than speed of light, but then make a big leap to "information is passed faster than the speed of light". And yes some physicists also had issues here.
I do agree that there are bad science communicators or people who "explain things" in bad faith. Or worse, scientists that start to believe in something and this makes them biased. The worst are scammers of course - though usually not physicists (there are couple, but you probably know about them). I mean I saw explanation of how "healing energy of the crystals" can be explained by quantum entanglement and "observation theory" 🤮.
But I don't think Action Lab nor most science communicators on You Tube are guilty of this. At least the ones I'm watching. They simplify - sure. But if small part of the audience takes something to mean something that science communicator didn't originally mean, Science Communicator can only be partially responsible. Especially if we mean people like those who will understand "This curve is determined by Planck's Law" as "It is Planck's Law that makes objects radiate/absorb energy". It's along the lines of "If Newton didn't 'discover' gravity, we could jump infinitely high".
And yes, it would be better if "determined" was replaced by "described". But then there will be a subset of people who will still think it's somehow the law that makes it happen.
Even if you produced absolutely flawlessly 100% accurate video with accurate wording - you will still have people misunderstanding it. It's just that the video will now be much less accessible to regular viewer. Science Communicators have to find balance between accuracy, complexity and accessibility. And I think that Action Lab manages to do it.
If I rub my hands, both get hotter than my hands! Have I violated any law of thermodynamics, or is it just work used to increase the thermal energy?
Mechanical work converted to heat by friction. Just like what brakes do.
@@Sekir80 it was a rhetorical question.
I study chemistry in my masters now. We learn a lot about the interaction between light and matter.
The idea, that light is just a mediator between matter blew my mind. It's like the tone that we make in order to communicate. You can change pitch (frequency) and decibel (amplitude) to form understandable words. Light is matter communicating with uts surrounding.
Check boson-fermion interaction.
And that light has no temperature is also freaky af.
Thanks for the video!
*its surrounding
The Bozo-Farmer interaction...?
this makes a lot of sense. I've always felt that the designation of lasers as "negative temperature" was just a lazy way to make the math work for something we didn't understand, but it being a nonthermal source makers much more sense than a negative temperature source. Then its designated as a negative temperature source because heat will always move away from a negative temperature source.
I can think of it practically like the relationship between being pushed by an object vs being acted on by gravity. the object pushing you has a finite amount of energy that it can transfer and so you will only move at a certain maximum speed (like a normal thermal source), but if you have no thing under you and no air resistance gravity could theoretically speed you up infinitely as its a constant source of energy (like a laser).
I know I'm saying anything profound but its nice to finally learn this. My wife jokes with me all the time by reminding me of "negative temperature" because I would get so heated about it.
The laser light is transferring energy. Whatever the laser is shining on is accumulating that energy so it is a question of time and energy not simply energy.
Well to be fair... Whatever gave the laser that energy also lost it at some point, so there is an energy equilibrium, but the system is probably on the scale of the earth. It becomes the universe if you use any elements greater than iron, like uranium in nuclear reactors. But at that point it would be mass-energy equilibrium ?
4:10 when you say "cleaning your teeth", i though you are gonna use laser to clean teeth lol
me 2😂
7:34 doesn't that mean you can heat an object more assuming you focus all of it on a smaller object since a smaller object won't radiate the heat as fast right?
At no simulations point in time, sink cannot be hooter than source
Technically no, but practically yes. Thermal emissivity is based on material and chemical properties, not physical dimensions, so a target of a certain material is always going to radiate energy at the same rate, regardless of size. While that's the technical correct answer, the practical answer depends on a lot of factors and that complicated math soup will usually result in a smaller target heating up more quickly and staying at a higher temperature than a larger target. Which would not be the case if you somehow conducted this test in scientifically ideal and perfect conditions.
Imagine that your targets are two cups, a small one and a large one. If you pour water into both of them at the same rate, the small one will obviously fill first, because it is smaller. Once it fills, the water starts pouring out over the edge; that's the thermal emission, radiating the "heat" away at the same rate at which it is being delivered. Once the large cup is filled, it too will start spilling over the edge and the amount of water spilling over will be the same as the amount spilling from the smaller cup because they both have the same amount flowing in.
2:39 crazy vending machine they got there.
Ikr... XD
lol
"Imagine if we shine ten million of them in the same spot" National Ignotion facility has entered the chat.
Yea, you are off by a order of magnitude or two.
@@boeubanks7507 iirc it's 100 or so lasers (don't quote me on that) but they are amplified SO MUCH that for the brief moment where it hits the capsule, it's probably the highest power (W) thing in the universe.
@mismis3153 Thank you for making my point. Also, I would be careful saying it is the highest wattage thing in the universe. That is a bold statement, cotton, when you have things like magnatars, pulsars, neutron stars, and black hole jets out there. If you want to say on this planet, I could go with that though.
@@boeubanks7507 After careful (google snippet results) research, it looks like the NIL lasers are about 5^-26 times more powerful than a pulsar.
5:55 I'm not sure that this is the whole story. If it were, then any monochromatic light source would do the trick, but if you let two otherwise isolated systems exchange heat via radiation through a monochromatic filter they'd still get to thermal equilibrium. In that case the relation between frequency and intensity (in connection with emission/absorption coefficients) would ensure that.
Also what is the "temperature" of a laser, where the light emitting atoms are "pumped" into an inverted state that isn't something that corresponds to a thermal equilibrium (AFAIK that inversion would correspond to a "negative temperature", one would characterize with beta=1/T in the statistical description to get continuously from non-inverted to inverted states).
I'm amazed by assistant's dedication!
Lol not gonna be me😂
This is a great video, I design laser engraving systems. We go down to spots with a size of a few microns to get some enormous power density. This is a great basic video explaining some of the phenomenon
comically small sun
I learned yesterday that we figured out what was diamonds were by vaporizing them, and then doing experiments to see what the gas was! This was in the 1700s!
One of the methods they used was simply lenses. How crazy is that. I've seen people burn rocks, but diamonds just using the sun is crazy to me.
He should do this himself.
Makes me appreciate glass. Where would science be without it. They used glass lenses to vaporize diamond to capture the gas in glass vessels to weigh the gas! Then used glass beakers to do the tests.
0:23 look super closely they did cross😮 in slow motion obviously
In a Thought Emporium video about "cold fire" they explained that thermal temperature is different from "electron temperature" is it possible these are related?
Isn't heating through Induction same? The heat produced is hotter than the source
6:56 no actually there's a limit plank energy limit
Did you say that you cannot focus sunlight to a pinpoint that is hotter than the source?
If I have a very large surface at 1000 C, and I focus the light (IR) to a pinpoint, the pinpoint will not be hotter than 1000 C?
Yes, no hotter than 1000.
@@nuclearmedicineman6270 How would the pinpoint radiate the excess energy away?
No, you can't get it hotter than 1000C with just lenses and mirrors.
@@DANGJOS You don't help anyone by just repeating the statement. The Stefan-Boltzmann Law works with an area, the magnification(in one direction) has an effect for the equilibrium of the heat transfer.
Conservation of Etendue
As a tube cutting laser programmer, this video makes me smile. Mine is only 3 kilowatts though.
I can give you the phone number of someone that sells stronger ones.
What happens if you get like a spherical array of those laser cutters or even stronger lasers, pointed them all inwards towards the direct centre of the sphere and then fire them at something in that centre point?
I believe that's the principle of the fusion reactor at NIF
It'll likely vaporize quite rapidly. It's basically a lower power version of one of the proposed methods of igniting fusion. Fuel is inserted into a pellet and it gets hit with high power lasers from multiple directions; the blast wave of the shell vaporizing compresses the fuel to fusion conditions.
@@DW-indeed no, the temperature of the NIF target is high (~10^7 K) but many orders of magnitude below the laser wave temperature
5:27 Question: how does LASER compare to SOLAR radiation? I think of the sun as emitting all manner of spectrum, based on something somebody said about Parker space probe data result ... What is the EM difference of focused LASER vs solar, thinking a minuscule Earth sized critter is in a straight line to the solar radiance, thus reasonably coherent beams of photons??? Just wondering 'bout Black Body radiation vs EM ... the rest was very educational, but caused me this question about exceeding limits. If a lens focused a particular wavelength, continually powered by the sun, how would the physical interaction effect result differently, laser vs specific solar radiation? (if the lens were focused in outer space without pesky atmospheric light scattering annoyance 😬) EDIT: I will search "what happens if you focus a laser Action Lab" based upon a comment.
For this you have to understand lasers, which this video doesnt actually explain at all. The key takeaway is 0:49 "Light doesn't have temperature". When sun shines on you, it is a thermal exchange. Radiation is what carries that exchange. Laser is not thermal exchange, when laser device shines on you it doesnt exchange heat with you thermally. Laser is the heat itself, which is produced differently than the blackbody radiation. Laser is magic that follows very exotic principles that are much more advanced than the widely known 2nd law of thermodynamics.
Laser is not a spectrum of light, laser is one specific wavelength. If you filter out a portion of the light spectrum, you will also reduce the heat transferred to you, as filter will absorb heat from filtered wavelengths. Thats how wine bottles work, they absorb part of the light to protect the wine. Tinted windows and sunglasses are filters too, but instead of filtering out a color, they pass through only certain orientation of lightwaves, absorbing the rest (thats why tinted windows make cars colder than no tint).
before i watched u i always got c- or d- in school but after watching ur vids for a few years now ive been getting a- and a+! thank you!
I used to run one of those LT8 laser cutters for various metal tubing. Thay really are amazing, and SUPER high tech. There are dozens of mirrors that the lazer bounces off before it goes through the lense (which is like a $350-500 lense). And thats not including the tube feeding and sensing system which I think is even more complex.
So where exactly is all this vaporized metal condensing?
Laser dust, aka metal dust. The exhaust is drawn into an air handler. If you want mars soil, ask for some laser dust. It's nearly the same density of air. Gets everywhere. Probably giving me Parkinson's in a few years.
@cashewABCD ok I get that but THIS thing is evaporating a LOT of it, do the filters have to be changed every couple of minutes?
Nope. Not usually filtered. Just spewed outside via the fan
Sometimes a water bath is used though@skydyverjym
@@skydyverjym our mazak and LVD lawyers draw the dust in a one foot tube. The collector is much larger. The dust falls out of the air when the air velocity slows. There are large filters in the top and then more filters before the air goes back into the shop. Underneath are two 50 gallon drums to collect the dust. One fills first allowing it to get emptied without shutting down the laser. Changed/ dumped weekly.
You can heat metallic things with "radio wave" frequencies using induction furnace...
0:36 they have INFRARED SENSOR CARDS!!?? This would be so useful for individual soldier laser warning if somebody is shining a PEQ on you.
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This is nonsensical.
I carry one in my wallet for checking if there's infrared light coming out of fibre channel optical cables and ports.
If the detector goes off for an infrared laser, it's too late.
Either you actively have a firearm pointed at you, or there are hot laser guided munitions on its way to your location.
It won't be much help at all, other than warning you of the inevitable.
Tanks have laser warning receivers for this reason.
so if you use mirrors and multiple magnifying glasses to focus sunlight from multiple directions on the same spot, you can heat the point up higher than the surface of the sun right? because then you can also put as much energy into one point as you want.
3:13 OK, this is messing with my mind... Laser at 30° angle(for arguments sake), round bar spinning, you'd expect the laser to cut a cone on the end of the bar, but the finished cross-section is a square?
There are sparks coming out of the middle while the laser is cutting. I'm gonna say it's cutting a pipe and not a solid steel rod. It's slightly cone shaped, but that would be a bevel on the outer pipe wall.
If you look at the piece that’s removed as it falls away you’ll notice it’s tubing and not bar stock.
It's a hollow cylinder, of course. You can see the (annular) "bevel"
Here is a question: Can we use fiber optic cables to carry the focused sunlight(maybe with multiple lenses) to somewhere else and direct all the light onto a single point. Can we achieve a higher temperature?
5:27 - Why? What is the difference between focusing 10 kW laser light on a pinpoint and doing the same using magnifying glass and Sun as a source?
as for infinitely high temperature, would there eventually be a temperature at which the molecules' motion approaches speed of light?
You can definitely make something hotter than the surface of the sun with just sunlight, you just need to focus the light to a smaller point. The problem is that any material vaporizes before it even reaches that temperature.
Yep, he was outright wrong about that.
No, he's not wrong about that. You can definitely get a higher temperature by focusing to a smaller spot but you cannot get a temperature hotter than the source. For the Sun that maximum temperature is just under 10,000 F; in practice you can expect about 5,000 F, few materials can withstand that.
@@HarmanRobotics evidently this argument has been going on on the internet for a while. Charge your laser with a solar panel and then nuke the crap out of what ever you want. QED.
@@HarmanRobotics Getting something hotter than the surface of the sun is practically impossible due to how little of its energy actually reaches Earth and because you'd have to have a magical way to input energy without losing much to the environment.
With that said, there's nothing in the physics theory that dictates that it's impossible to use sunlight to heat something up hotter than the sun itself. All you need is a way to get the energy from the sunlight into something that won't lose that energy due to radiation and conduction once it's heated up. This video mixed up 3 concepts that have nothing to do with each other. The line about sunlight is that you can't use a magnifier to focus more energy into a spot than what already reaches the magnifier itself.
The limitation of temperature only applies to conduction and convection processes in matter. Outside of that, electromagnetic waves could theoretically inject energy into a system indefinitely and literally heat it up to infinity.
Just need them powerful enough to work at a long range, and you have a Defense wall for hypersonic weapons.
Israel's iron beam
2nd law has to deal with entropy NOT temperature, and it refers to an "isolated system". Temperature is a simple interpretation of entropy moving from hot sources to cold. What's your total system in the 10kW laser example?
Does this mean that if you had to point the weaker laser at a sheet of metal for a long time it would end up getting red hot.
( Ignoring the fact that the atmosphere will most likely cool it down at a quicker rate. )
I kinda like seeing how this channel went from the clickbaity hydraulic press and vacuum chamber videos to thermodynamics, heat transfer and blackbody radiation, even it's on a rudimentary level, this is still very informative and interesting !
That's a 10KW Trumpf (note the 'f' at the end) laser cutter. I use to work with a 4KW unit, of the same make, years ago. Those particular units are used to cut metal. Steel, most often. It can cut finer, and more accurately, than a plasma cutter. Though the plasma cutter is about 1/10th the cost.
Then you should also know that these lasers are not vaporising, but mostly just melting the steel and its the jet of gas that makes it "disappear". That's very important feature. We couldn't cut steel without it.
The closest invention to my emf kite is a cathode ray tube. Which does push but I’m curious to see if you can get push with open electricity and no vacuum
What if laser is not a heat energy, but a motion energy? Ok i may a little bit confuse but just imagine like starting fire from two wood by friction ? Does it the same or different?
As a child in the 70s, I was fascinated by lasers. I remember how outrageously expensive the first laser pointers were.
In Japan (or China? Sorry, don't know exactly), branches are removed from the tops of trees by laser. It looks very impressive. Lasers are simply cool (and hot). :-Þ
Even though the laser and microwave can heat objects and increase the temp above the input power, it has a continuous input of power to replace the power emitted.
It is not measured in the same way as a thermal source emitting energy, as the laser and microwave has power being added to it as it expends the power.
Wait. How does the infrared sensor plate work? It absorbed the infrared and emitted red. Things don't flouresce a higher energy light...
Great observation! Before use, the phosphor has to be charged with visible light (e.g. sunlight), so that, when hit by infrared light, it releases the energy stored during the charging process
yes it is charged by the light from the room. If you hold it in one spot for too long it discharges and won't show any red
A laser differs from a regular light in the fact that it is monocromatic, coherent, and directional.. so, how can a laser be able to heat something to infinity while a concentrated regular light only can heat something up till it gets to the temperature of the source of that light?? What is the difference in the business end of the light, when impacts a surface?... I wonder..
This is exactly my question. The video didn't really explain why laser light is different. Perhaps the coherence of the light is the big difference here? You could surely filter out all the frequencies of sunlight to a single frequency, and concentrate it.... but you couldn't make it coherent.
@@stevesether It kept me thinking, could it be that "light transferring energy" behave as heat or electric current?, where you have "temperature" and "heat" or "voltage" and "current" respectively.. let's say.. an impulsory force and an ammount of energy being transfered.. once the force is in equilibrium you can't "push" anymore energy to the other side... Laser might have, or be able to get, an arbitrarily high level of "force" to "push" while for sunlight or any random white light the "force" is only as strong as for the source of that light, so it cannot achieve higher temperatures. In such a case, what would be the "voltage" (or pressure making a fluids analogy) for the light? I don't know..
I think he misstates the science. It is in fact possible to used concentrated light from the sun to exceed the temperature of the surface of the Sun. The Odeillo solar furnace in France achieved a temperature of 10,000 C. According to what I read, there's no upper limit on the temperatures that can be achieved. EDIT: this paragraph is wrong! See follow-up below.
What you cannot do is focus the Sun's light down to a single point, because the Sun's light is disk shaped as viewed on Earth, so even at perfect focus, you always get a disk.
@@yeroca Thanks. This makes more sense to me. I'll check out the odelio solar furnace.
@@yeroca Where are you seeing that this furnace can achieve 10,000 C? The cursory searches I see say it's more like 3500C.
what about the entropy of the laser's light. doesnt it would theoretically be a maximum threshold to how hot we can heat up something and not just the energy output of the laser?
4:35 come on...
😂
... Could we create a new heater as an appliance? Would it save energy-wise in terms of energy efficiency?
Can you get blind from infrared light, that you can't see?
Potentially. Something in the infrared range like 900ish nm, doesn't make you feel hot, but it heats up tissue inside since it penetrates the body and you can end up damaging your eyes. The sun is blasting you with broad spectrum infrared which is good for you but the eyes are very sensitive which is why you don't look straight at the sun.
I am confused, wouldn’t there have to be a limit to temperature, otherwise the particles would end up vibrating faster than the speed of light.
I think the rough answer is that the kinetic energy of the particles goes up faster than the speed. This is because the relativistic mass of the particles goes up with their speed. To reach the speed of light the particles would need to be infinitely heavy - which never happens. In a sense the energy creates extra mass. E = mc^2 comes in here somewhere, I think my explanation is basically correct, but probably no use the latest way of explaining it.
The kinetic energy of a (massive) particle moving at the speed of light is infinite, which would correspond to something like 'infinite temperature'. No matter how much energy you put into an object, you can't make it go equal to (or faster than) the speed of light.
At first, I thought the temperature of an object couldn’t exceed the temperature of the source, but lasers just proved me wrong! This is insane, I have to try it!
How is this connected with this weird negative temperature of lasers you came up with in an older video?
Well, lasers have a population inversion in the internals of the laser. So if you had to define a temperature for the laser it would be a negative absolute temperature which is hotter than any positive temperature. But the problem is that in order to define a temperature the system has to be in thermal equilibrium, and that is not the case with lasers. So, although it can be explained by the fact that they have a negative temperature, I think that this explanation is more correct.
Lasers are not matter, they don't have intrinsic temperature, be it positive or negative.
Grew up watching your content. Always learning something new. Thanks for being around! ❤️
Now, what about total reflection, like in glass/air interface under specific angle ? It does not depend on conductivity, so it should not decrease... Would probably require a glass block and heating it evenly would be even more changing
2nd law of thermodynamics is about entropy change in close system. It means heat flow from hot to cold in the case of conduction. In the case of laser, it involves electrical energy input, excitation, spontaneous emissions, stimulated emissions. Each step is govt by thermo law. Kind of like an engine cycle.
Yea how do you cut through steel and then not cut trough whatever is behind it for some great distance?
Can we use laser for soldering electronic components?
How does matter absorb energy?
Atoms and molecules can absorb energy from electomagnetic waves because they are made from charge particles (electrons and protons). The oscillating electromagnetic field in the waves makes the electrons in the material wobble around a lot, which cause the atoms/molecules wobble around a lot too. This gives the molecules kinetic energy and thus heats them up. The specifics of how this happens is a bit complicated (look up "dielectric heating" and "electric dipole moment" for more info) but that is the gist of it.
@Aphobis I imagine molecules talking to each other.
Hey Bob, that isn't a lazer beam is it?
Kevin; 'It is! We're totally effed!'
Bob; 'I'm shaking like a leaf over here!'
[POP!]
Bill; 'There goes Bob. Straight to vapor! The poor b@s+Rd didn't have a chance.'
Kevin; 'You're next Ronny!'
Is electricity the same ? Does electricity have a temperature ? Is there a maximum temperature a certain voltage can reach ?
Remember this is also related to negative temperature, which he's also done a video on.
What if you put the sun inside the laser stick and focus it's entire energy to a single spot? Can't it still get hotter than the sun itself?
Because like the battery source or the electricity flowing in the magnetron also the sun has an active energy source with fusion.
It was cool seeing those Trumpf lasers. I used to work on Trumpf lasers, anywhere from 8kw to 24kw. I mainly operated a 24kw laser paired with a 3060 gantry. It was the first 3060 in the United States to have a 24kw resonator paired with it. I would do all kinds of stuff, from really thin aluminum, to 2 inch thick steel. I knew all the little tricks and techniques to get that thing to cut any material with no laser burr too. The science involved is quite complicated.
So what's happen if you put a black steel ball inside a vaccum chamber and point your small handheld laser on it ?
well as it is emitting energy, and that energy is usually measured over an area not a point, so you can concentrate that energy by reducing the area that it is dissipating energy over.
so yes you can focus a collimated beam of light and make it higher powered.
at one point you hit the diffraction limit for a given wavelength
@@omblauman umm a single wavelength of light will diffract to a single wavelength of light.
@@johng.1703 yes and you can't go lower and increase power density infinitely
@@omblauman what are you going on about? focusing a single wavelength just means concentrating more energetic particles into a single point.
@@johng.1703 but you can't go on forever concentrating and at some point you are re-radiating all the power you are concentrating since radiation goes with the 4th power of temperature. I might not understand what you want to demonstrate though
I work for a company that makes kW class cutting lasers. And I can tell you that the dust that comes from cutting metal is a pain to deal with. It's incredibly fine since it is condensed metal, essentially a percipitated fog of tiny particles.
does all of the suns radiation come from it's temperature or are some of the photons directly created by the fusion reaction. similar to a laser that would mean you could get something hotter than the sun.
So can we use one of those 10 kw laser as a security system?
The Chinese make fairly cheap and powerful rust cleaning lasers. One could I'm sure play laser tag with the neighbours.
So if i understand that right: You can technically focus a laser as tight as a single Hydrogenatom and get it infinetly hot?
Theoretically it could get as hot as plack temperature, where the wavelength of the thermal radiation reaches the planck length. So about 1.416 x 10^32 Kelvin.
That is as hot as anything can get.
question , If a laser runs for say 1 hour just pointed at nothing , say out to space , and you measure the lasers head body cavity temperature , Then under the same conditions , but , this time the laser is being used to say , cut metal , Would we measure the lasers body , or head, or cavity etc.. to be hotter ? In other words does a laser get hotter if its doing work ? has a load on it , compared to no load . Thank you very much.
Once the light is emitted from the laser, it does not interact with it anymore, whether it ends up hitting metal or nothing, the laser has no "idea" what happened to it because the information does not come back.
One exception would be if some light is reflected off the metal and comes back to hit the laser, heating it up, but considering your question I think this is a technicality
@@Jules.D Thank You for replying , And so quickly . That is what I suspected . I'm too lazy today LOL!
so is there a way to use this information to create an energy device that gives more energy that it creates
if i can see the infrarred in the dark plate of the radiometer, ¿can y build a sensor black plate to watch the iifrared light by putting it into a transparent box in vacumn? sorry for my bad english, saludos desde argentina
When two coherent laser beams destructively interfere with each other (like in the LIGO detector), where does the energy go?
It goes to the Bahamas
What if you split blackbody light using a prism?
Dude, what were you eating!? 4:52
💩
I have a question but it is not related to this video it that where does the sound actually come from when you snap your finger's
What does the infrared sensor card look like in front of a infrared heater
LED flashlights sort of do this since they emulate a black body source. Used to have one of those Nitecore lights and with great difficulty it could get to charring and smoldering paper.
Does this mean that you can have a laser soldering iron?
3:30 Young Action Lab from another diamension?
Light cutting stuff, the very thought blows your mind, never mind everything else behind it
37 years ago I earned an Associates in Laser Electro-Optics Technology. That 2 year degree kicked in the door for a long career. I ended up installing, repairing x-ray equipment. I earned my degree 37 years too early.
What would happen to a graphite rod in vacuum chamber, when you shine laser on it?
Should have gone to the styro Pyro that guy can build a laser
So would induction stove tops technically do this too?
Is this also related to conservation of etendue?
4:24 - I got all excited - I was really hoping you were about to say laser toothbrush 🪥
Now that would be cool, lol
Whens makita coming out with the 18v laser blade
Wow it's amazing, science is amazing.
Great video, great summary at the end of it. Thanks!
So if I understand it correctly. The laser just turns the light energy into heat energy at the point of impact. The total energy of the light energy will be more than the energy required to heat up the material by X amount. other will be lost in form of reflected light or other forms of energy. You literally said it. light has no temperature. so no paradox?
the laser just delivers energy, like any source of EM radiation. the material absorbs some of it, heating up. as it heats up it also radiates back that energy as thermal radiation, eventually reaching equilibrium when it radiates the same amount you put in. the maximum temperature you can reach is then limited by how tight you can focus that radiation, and thats where lasers are very special.