Bad Beams? | How divergent are lasers?
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- เผยแพร่เมื่อ 26 ก.ย. 2024
- Laser beams are amazing to watch since they appear like a string of light. Not like a wash of illumination from other light sources.
But does a laser beam spread out? Does it diverge - getting wider over distance? Let's measure the divergence of my cheapest and most expensive lasers!
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Measuring power and wavelength of my strongest lasers, including the Laserglow Hercules: • Strongest LASERs in my...
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#Divergence #Laser #Brainiac75
"My method is more like......ghetto style"
*This is a certified keychain laser classic*
Lol
Thanks for Pointing us in the right direction, and keeping us on the straight and narrow.
Hehe, nice touch. I do like to guide with a laser sharp focus x) Thanks for watching!
At 3:00 - I get so excited every time I see speckles. Currently doing a research project at DTU Photonics regarding speckle, and hopefully my first article on the subject will be published within the coming months!
Can you give a brief description of the generative phenomenon? Micro scale destructive interference within the cavity (no idea if this is a thing, just the first thing my intuition spat out given the pattern...) ?
@@mduckernz In the case shows at 3:00, it is the roughness of the surface that gives rise to speckles. It has to be a surface that reflects diffusively for it to happen, which the computer case does.
4:30 the inverse tangent is irrelevant at the small angles and low precision you're using though, and in fact, in some contexts this type of divergence value is actually _assumed by default_ to be a sort of "first order small angle approximation mrad" rather than the "proper circular mrad with trig stuff". But basically, you can just get rid of the trig function entirely and substitute the parameter, cancel the 2's, and do (1.5 - .25)/1190 to get exactly the same value easily within your available precision.
Yes, the inverse tangent is linear at very small values.
Will happily take ghetto setups as long as the units used are ISO units :)
I never really thought how big of a factor laser divergence is until now when looking at long distances. Very interesting!
I'd like to hear more
...about those two subwoofers. ^^
Me too!
Basshead 🤙
Larger multimode diodes have a fast axis and a slow axis. Because of diffraction limitation physics, a smaller beam has a larger divergence (all else equal) which explains much of the reason the red diverges faster from the smaller initial axis. The beam correction optics principal is therefore simple: Expand the smaller (initial) axis to reduce its divergence.
someone that know physics on youtube.
0:43 the way you said “hi” put a beautiful smile of welcome to my face!!
Hehe, I may have been particularly frisky the day I recorded that voiceover. 'Hi' is usually the first word in all of my newest videos, but this time I felt like mixing it up with a different intro. Thanks for the fast watch!
@@brainiac75 OwO, frisky you say?
Yes, Caroline. As in the official definition of the word: playful and full of energy. Not the slang version ;) And remember Danish is my daily language, I may not catch all nuances in English xD
You uploading today was the highlight of my day
Such an amazing video, keep up the good work!
Thanks, Caroline. Much more to come!
You can use a mirrorless camera to capture the beam profile. Moreover, if you capture it in several planes you can completely recover the phase profile which is the all information you can get about the beam quality.
Also you can improve the quality of the beam by passing it through a pinhole.
I was honestly just checking to see if you have any new videos up and I saw this!
Thanks for the upload!
Great :) I usually upload last Friday in a month, but sometimes I need the last weekend to finish the video x) Much more to come and thanks for the fast watch!
The divergence depends on the quality of the lenses used and collimation done well with distances of 100m from the laser.
You can't determine the divergence if you don't make good collimation and don't use quality lenses.
Not really. Even perfection will still diverge due to the diffraction at the edges of the beam. NASA lasers bouncing off the Apollo reflectors are several miles in diameter by the time they reach the moon. This can not be improved on no matter how good the collimation is, it’s physics.
3:06 if you guys want to know what that integral equation means, it basically is just defining the beam intensity at some constant sigma, then you take the real number operator and then find the root of the intensity integral, then you define the x and y plane (since it is not like we have a complex Cartesian coordinate plane here) and then you define it if the intensity is zero, in which is the bottom part of the dividing of the two integrals, in the end you are just simply measuring a interval in integrals from the divergence at infinity, or at negative infinity. A more simple way of doing the exact same thing this equation does is to simply imagine the light as a hyperbolic wave function and then to measure the amplitude from there, sure it may be more expensive, but easier.
1:36 Umm, lets talk about those 2 GIANT subs you have! : P
Best method to measure the spots is to use a camera and export the beam profile. Then you can correctly identify the intensity and edges.
A scale in pic allows calibrating the pixels to real world scale.
I found it amusing to be watching this while I align a 4-laser system using the 13.5% measurement. Well done with the resources you had at hand.
Nice Friday timing! Love the quality of your videos. Keep up the great work!
Always try to make it on a Friday. Gives me the weekend to focus on the next video x) Much more to come!
Wow another month has flown by. Thanks for the upload
watching from Germany. Keep up the good videos !!
Great video! Finally i have something good to watch :D
Cool diffraction rings. The filter can also cause divergence (or convergence) if the sides aren't perfectly parallel and flat.
Gotta love how the cheap laser has the best divergence
Many years ago, we set up a helium neon laser on a tripod at a friend's house, in the valley. As I recall it was only 5 mW, but it was physically pretty big. An aluminum cylinder maybe couple inches in diameter, and 8 or 10 long, and ran on a high voltage power supply. It gave a nice crisp red dot, not terribly bright. We then drove to the mountain peak, around 5600 feet, and maybe 15 miles away as the crow flies. Over the radio, we talked with him, as he tried to get the laser pointed at us. He first tried a handheld spotlight, so we'd know exactly where to look, but we never could see that. But he finally got that laser lined up and, while it was certainly not blindingly bright, it was without question at that point the brightest light visible in the city below. It would have been cool to hold up a big white sheet, to see if we could see a circle, but I don't think it would have been visible, even in the dark up there, what with all of the light pollution. And it very likely would have been a circle much bigger than a sheet at that distance. If the output was 2 mm, and we were what, maybe 20,000 meters away... Even a very good laser would have a lot of divergence. Would be interesting to calculate how big the "dot" would be if it was a 1 milliradian laser. It was pretty cool though. A fun night. Well, let's see, if it was 1 milliradian, and the initial size was 2 mm, the size at 20,000 meters would be... 40 meters? It was probably a bit better than that as it had come out of some old piece of equipment that was probably expensive back in the day lol.
Interesting to see how much your Hercules diverges, I am betting you could easily get a better dot with adjusting the focus. DPSS lasers tend to have really low divergence overall. It's a huge reason I got into messing around with DPSS, that and such pretty and magical crystals inside. Nice video as always!
I am always impressed by your model car collection when I see it, you should give us a tour. :)
"won't melt when I test stronger lasers"
styropyro would like to have a word with you
Thanks!
Glad you like it, TriPham :) And thanks for the generous donation!
What is absolutely beautiful is in the winter when you have large lazy snowflakes falling, shine a laser out a 2n story window cross the field. As snowflakes fall through the beam, they flash brightly. Very pretty. Best if there is very little wind and the flakes are large.
as a hard SF nerd, allow me to give a few tips to reduce a laser beam divergence (this is purely because it's interesting, and not meant to be practical ^^)
1 - use good correction optics.
2 - increase the size of the aperture (the output lens or mirror) of the laser. (that's why military laser always have telescope-like aperture)
3 - the shorter the wavelength, the better. (in atmosphere you can't really go past soft UV as the atmosphere absorbs shorter wavelengths, but if you are in space feel free to use hard X-rays if you can find a laser and optics able to deal with it ^^)
Would love a video on your entertainment system speakers!
Wow, I have never been so early to a Brainiac video, thank you!
Same
Very early indeed, Jokūbas! Thanks for the fast watch :D
Thank you for the video!
Thanks for the fast watch ;)
Nice video .
I really appreciate your hard work. 👍👍👍👍👍👍👍
I wonder if one of the old helium-neon gas lasers would be better?
Great video👍
I'd be interested to know how divergent a laser scanners beam is. We have a Trimble unit that can measure up to 340 metres, but as it's not using visible light, it'd be hard to know.
It's probably an IR laser, so you could use an IR detector card to make the spot visible. If it can scan at good resolution up to 340 meters away it must have pretty good divergence. Would be interesting to test, if they don't specify the laser's divergence. Thanks for watching!
@@brainiac75 From what I can find, it's about 0.177 mrad. Thank you for making your great videos!
Wow, that's not pretty good. That's very good divergence! But again, it is needed if working at 340 meters distance. Thanks for the info.
@@brainiac75 Why not just use a camera to "look" at the beam?
That integral will give me nightmares.
The keychain laser is extra impressive considering that it's red- doesn't the minimum divergence Increase with wavelength?
Yes, although it's a low power diode operating in single mode. Higher power (especially blue) LDs operate in multimode, and thus have lower beam specs and higher divergence!
Huh, I was thinking that divergence would be inversely proportional to wavelength, kind of like diffraction…
The concave lense may converge more to keep focus more because most pointer had low quality lense
Are those ringing marks (from the waves interfering with each other) at the far point?
4:04 heyyy! don't underestimate windows calculator 😄 especially the latest version that came with Windows 10 is great.
Hehe, I actually do use it a lot when making calculations for my videos. Thanks for watching!
Nah, the windows 7 one was way better for serious calculations, you could click into and edit the expressions in the history
@@TheBackyardChemist You now can too. Also it's just a port from windows 7 version to Windows 10 WPF
@@drozcan I wouldnt know, I actually hacked the win7 calculator into win10, but thanks for the tip
(laughs in Speedcrunch)
I think you might be misjudging the 1/e^2 point. Weber-Fechner law says human brightness perception is logarithmic compared to the actual brightness.
Air pressure resulted in x axis more diverge than y axis. Just like submarine presure change depending on ocean floor
I don't know whether or not you have everything necessary for this kind of test, but another thing to look at would be how they diverge in a vacuum. For high power lasers that run hot, the air in the path of the beam may get heated up and cause a blooming effect. Plus, higher wavelength lasers diffract in air more
You should try a long tube laser for better divergence
the shutters from 8:40 laser could use some recalibration, or the mirrors for directing multiples sum of lasers, did you drop it or something?
Our Faro S150 Laser Scanner is 0.3mrad full beam with a beam diameter of 2.12mm at exit.
The laser measure adds it's own length so you can, for example, hold it against a wall and measure the distance to the opposing wall
My cats would have gone crazy during that experiment. :D
Is it possible to use a small parabolic reflector to improve beam quality?
too bulky even if small, frensel lens works much better
MS calculator (or any other PC calculator) is so much easier to use with a numpad than with a mouse. Even the standard number keys + operation keys are so much faster. If you do use the numpad, make sure to enable num lock before hand.
Totally agree, but for viewers wanting to replicate the calculations in one go, it is much easier to follow along when I use the mouse ;) Thanks for watching!
@@brainiac75 Or you could do what I just do and use an (i)python shell as a calculator. It may not be as easy, but it is much more powerful than a traditional calculator.
The ones that have a focal point before crossing and spreading again... Isn't that a negative divergence from the actual source?
I want you to make a video about your scale model car collection.
For a laser used as a pointer in presentations, having some divergence might be desired so that the dot in the target maintains a constant apparent size regardless of distance. I'm just not sure how much divergence would do that. Maybe it isn't much at all.
I love Your videos!
Wait, so a milliradian is not a millionth of a Radian, like one would expect, but is in fact a defined metric unit exactly equal to the definition at 1:10?
Or is the 1mm/1m divergence just approximately equal to an actual milli-Radian, or 10*-6 Rads, as an actual angle?
Thank you!
How feasible is it to just sticka lense in front of it and achieve zero divergence? Like obviously not since the manufacturers likely wouldve dont that already especially on the expensive laser, but why not?
If there is a chance you could explain what is happening with near field and far field divergence, it'd be really nice. I can't seem to wrap my head around that.
TIL that the cheapy 200mw green laser I bought (that I always thought was more powerful than 200 mW because it's really bright) that I spent weeks getting a very columated beam on, swapping lens and filters and all that, is insanely columated at .72 mrad
Nice
Why were the diffraction rings formed at the spot at higher distance for the first laser?
Wait, this is not the test for divergence that they taught in Calculus class!
What's going on here? Have I been bamboozled?
:D
Hey there, you seem to have resources for something a little more serious and important. How about you built a Michelson Morley Interferometer and rotate it VERTICALLY, that would be awesome, and you get to prove some of that Aether you've mentioned in the beginning
01:59 - those are some mean subwoofers bro!
Heh not surprised the cheapo key chain was the lowest since was almost certainly a single mode diode. I have lasers that range from super tight to comically wide divergences. If you have an HeNe you should check it. If it's TEM0 it'll probably have a tight divergence. Or at least I seem to remember it being that way. I could be way wrong. Too bad I don't have a place to set up my big HeNe tube and my argon laser right now or I'd try it out.
You are correct. HeNe lasers have far lower beam divergence.
I have several models. One is about 12" between the mirrors and produces a spot of about 1" at 1 mile distance.
Basically the beam divergence is defined by the number of wavelengths between the laser cavity reflectors.
In simple diode lasers this is a few mm or so.
redrok
My favourite videos are the eye annhilationator videos
More laser videos to come ;) Thanks for watching!
Let’s dive into juicy science!
Keychain probably has a lot of infra-red
Could longer ruby help keep laser focus better
Er det muligt at få laser pære som man kan købe til bil, og så tilføje et filter så den kan lyse mere som en normal lytte? Fordi de lyser maget langt, men det er ikke rigtigt bruges når det er sådan at lille pånt.
Thanks for sharing this amazing video. Science is so amazing 😃❤️
You're welcome, Sofia. Science is indeed in every amazing thing ;) Thanks for the fast watch!
im just going to assume that the price/quality of the laser will have a big impact
Super fed video 😉 igen igen..
Men når du skriver/siger ud i det uendelige vil det så sige at laser som vi kender dem idag er en lyskilde der lyser uendelige langt og kan kun stoppes ved at en bryder "strålen" ???
9:46 Skip the "quick message" (9:17 is where it starts)
You should have used mirrors- by counting the amount of bounced you could easily multiply the distance.
Wait, should not you measure laser spot in a vacuum ? Why you shouldn't if it's interfere with gases in atmosphere ?
Is there a 13.5% ND filter that you could use to obtain a reference brightness with a camera with manual exposure and aperture settings, by locking the settings such that the ND-filtered beam is barely clipping at the brightest spot, and then checking how big the clipped patch is when you take a photo without the filter with the same settings?
3:04 Why would you write it as definite integral from - infinity to +infinity, lol? It's basically the same as indefinite integral.
dont think those are the same
actually you are incorrect, a infinite integral does not measure antiderivatives of a certain function of x, however a indefinite integral, just because it measures antiderivatives does not mean it is a infinite integral, unless you define that in the parametrization or in the number to approach at the top of the integral, and also he was trying to find the derivative value not the antiderivative function.
Hmm... your audio system looks interesting
But we never got to see how the youtube button on the Bosch instrument works.
Hey guys - what difference does divergence make to the width of the laser after it is expanded through a simple lens or mirror? If the divergence is 2 mRad for one laser and 4 mRad for another, will their spot size after expansion differ?
you can easily simplify the calculation.
taking the example of the last laser:
2mm at the start, 28mm at 11.9 meters
28-2 = 26
26 ÷ 11.9 = 2.18 😉
Thats true
When x is really small, tan(x) aproaches x
So arctan can be ignored because x is on the order of 0.001
INFINITE BRIGHTNESS
Would it be possible to use retroreflectors or geometric mirrors inside the laser housing to make the divergence near 0 mrad? Or is that what is already happening and its the quality of the mirrors that determines the divergence?
I kinda wanna figure out how good my 50mw Astronomy Laser is. On misty nights I can focus it to a point where it ends up terminating as a bright dot in the night sky.
over 2 milliradians of divergence, that's disappointing for a CNI module (the Hercules). I've always been told they were some of the best in the way of beam specs.
Dang!!! Do you have a large enough subwoofer setup???? I bet that baby really bumps!...........
So much MATH
So is it bad that the expensive lasers have high divergence then a cheap red dot laser? Or is it because the powerful a Lazer is the more it divergences?
In theory, there's no link between the power and divergence of a laser. But in practice, strong diode lasers tend to have multiple emitters. They need more high-precision, expensive correction optics to get good divergence.
The difference in divergence between the keychain laser and the expensive Hercules is mostly due to totally different lasering techniques. The 532 nm green is much more complicated to achieve than the 650 nm red. Thanks for watching!
@@brainiac75 Divergence increases with output. Adjust the output of the diode through it's power supply and measure.
It depends on the quality of the laser, no?
4:50 a small mistake, You saying that it need to be multiplied by 1000 to get milliradians from radians, but it’s actually vice-versa - You should multiply milliradians by 1000 to get radians (as You actually do)
Knowing the mrad could you make (buy) a lens to correct the divergence to parallel?
No
Hello braniac how are you how is your day. Hope you are doing well.
Hi, anonymous. Video release day is always a great one for me. Means I once again managed to complete a video x) Hope you're fine too and thanks for the fast watch!
If we shape the wave guide in a way that it program photon to spiral in in a proportionally to distance so it never diverse hopefully by shape wave guide wall with screwed like wall that spin or spiral outer photon keep spiral inward prevent divergent. Program light and hologram is the future of uploading soul into forever life in light
Haha, you didn't measure the range finder! =o) Might be the best of the bunch? My range finder Bosch GLM 80 goes from about 5x2mm line to about 12mm diffuse roundish shape in 8,6m.
Интересно, а автор сможет измерить расстояние до луны с помошью лазера, но без уголковых отражателей ? 😃
Я недавно был в Пулковской обсреватории, и там нам рассказыли что это было замеряно по отражению лазера от луны с помошью телескопа. Причем сам девайс, "водородный вычислитель" - который вычилял время прохождения луча туда-обратно стоит там-же, и сделан на лампах !
With the approximation that you are using, it doesn't account for the possibility that a significant amount of the total energy of the laser could go to regions under 13.5% energy density, right? If I'm wrong, please tell me how.
You didn't measure the divergence of the laser measure. :-)
It would actually have been interesting to see the divergence of the actual (I guess it's IR) measuring laser. The divergence of the pointer laser is less interesting.