ฝัง
- เผยแพร่เมื่อ 5 พ.ค. 2024
- Episode 63
#laser
#electronicscreators
What happens when you reflect a Laser beam back on itself?
This unusual Laser system from a Particle Counter does exactly that!
Why?
how does it work?
Let's find out!
Sams Laser FAQ The PMS/REO External Resonator Particle Counter HeNe Laser
www.repairfaq.org/sam/laserhe...
External Passive Cavity Laser patent:
patents.google.com/patent/US4...
Previous teardown of the Laser Particle counter:
• LASER Particle Counter...
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0:00 Intro
0:12 Helium Neon Lasers!
0:53 Brewster Window Laser
1:46 Unusual Particle Counter Laser
2:44 Sam's Laser FAQ
4:02 Patent External Stabilized Passive Cavity
8:25 Laser Teardown
9:05 Optical Bench Setup
9:45 Laser Demo
12:43 Credits - วิทยาศาสตร์และเทคโนโลยี
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This is a classic strategy we use to ensure our lasers are properly back-reflecting so that we can use it for alignment.
This was fascinating! I recall playing with a HeNe laser in 8th grade science in about 1970. I "killed it" by reflecting the beam back into the output and was VERY relieved that it came back on after being power cycled. Now I'm going to have to go read more about HeNe lasers to learn exactly what I did! Thank you.
If sold to a school presumably the manufacturer ensured the failsafe because it's guaranteed some curious kid is going to try to send the beam back from where it came.
Haha! That sounds like some shit that I would have done. A real, "Oh crap..." moment.
I am guessing (and it is a guess) that the laser sends a startup voltage pulse for power on. Then maybe u shorted the steady-state by clearing the population inversion (so then drawing too much current) . Then I suppose an internal circuit -breaker triggered
got to love those "bare" HeNe tubes glowing...
Since it says that it forms a resonant cavity, doesn't that mean the distance needs to be calibrated to some small fraction of a wavelength, so that a standing wave pattern can be formed by the back-reflected beam? But that's like maybe 600 nm! Is this really made that precise?! WOW if it is.
theoretically, yes.
practically, no, because every minor fluctuation in optical length (from temperature, density of the air in between, ground shock, etc...) is much bigger than any misalignment of the mirror itself could cause. These fluctuations don't usually ever matter, because even a laser doesn't emit on exactly 1 frequency - it still has a bandwidth - and if the wave coming back into the laser medium doesn't resonate anymore, a close neighboring frequency will be amplified instead and a different mode will take over.
I worked with helium neon lasers at Intec back in the 1970s. We use them for automated inspection systems along with a scanning multifaceted mirror system and a photo multiplier tube. The whole thing was timed like a television scan line system and we could see a trace of the light levels across the width of the product web on an oscilloscope.
"Product web"?
Sounds nice.
- spider
Ive been an electronics geek over 40 years. I have always had a love for lasers. Had my first HeNe tube and power supply kit from MPJA and All Electronics co when i was 8. I have owned dozens of lasers over the years from HeNe to Diode to Co2 to Nd:Yag never heard of or seen a speaker used like this. Very interesting.
Now you have new experiment material for a few more years! ;o)
Everyone when I walk in front of the projector dressed head to toe in retro reflective paint:
joe momma
Very cool. Super interesting use of a multi mode laser. You don't see that often.
For the diy test with the other HeNe, try adding a lens and put the flat mirror at the focal point to make a retro reflector that will match the divergence. An AR coated lens might be needed.
I will try this in the lab if I ever get some free time.
Of interest, a very similar principle is used in HeNe ring laser gyros to modulate them around their instability point.
always wondered about using a third mirror, now I know. Especially the need to vibrate mirror, etc.
thanks
Awesome. I have never heard of that before. So cool. Thank you!
Thanks Les. While studying I made some research on HeNe lasers in semiclassical theory, especially in population inversion in some situations. This partly falls in that range. I can not immediately sort out what is exactly happening hre without studying it in more detail. Hoever, this is interesting.
Wow, this was fascinating! Thank you.
Thanks!
Don't cross the streams! -Ghostbusters
I learned about how lasers work in the 67 using rubies but never have understood doide lasers.
In the 80s my dad worked for Coeherent General and we had these types of lasers laying around the house and I got to play with them all the time. I was the cool kid with a laser. At the time the company was using lasers for precision cutting ceramic tile layers for the space shuttle's heat shield. I wish I still had some of those failed samples but they were thin and broke very easily. I had no idea what I had at the time.
That sounds amazing! Yeah, same, there is lods of cool stuff that has passed through my hands, and now it's gone! As a consequence, these days I'm a bit of a hoarder!
Thanks!!!
Good useful info!
Congrats on Ieee publishing your paper
Thanks and thanks! Hopefully I will get more published :-)
Doomsday device: Reflecting the power back into the tube amplifies the power with each pass as it passes through the external optical cavity. The energy rapidly climbs until it begins to cause the air to laze as an optically pumped UV nitrogen laser. Power continues to climb as both lasers bounce back and forth in a positive feedback loop until temperatures climb enough to begin to first cause chemical reactions in the air (ie N2+O2 -> NOx, etc), then as the power continues to increase, the air undertakes fusion, which if sustained further, causes fusion ignition across the entire atmosphere in a rippling wave of destruction as all the atmosphere fuses, destroying all life on earth. Then we have to wait for another event for life to begin again. Don't try this at home.
That was wicked!
Most interesting. Almost always something new that I've never seen in detail on here!
Thanks! There is allsorts of cool, but obscure and forgotten tech hidden in old journals and patents!
Fascinating! Makes me wa t to play with old HeNe laser again.
He-Ne's are beautiful!
I used to have quite a collection of those old tubes. They were so fun to work with back in those days. Good times.
They are beautiful right?
I found your channel while researching how to de-bayer raspberry pi cameras, and I appreciate the hell out of your work. Catching up on your library now, but may I ask what you think is the most current way for a maker to record video in the UV spectrum? Does your video from 2 years ago have any potential updates? Or, hopefully, is there an easier/cheaper solution than burning the layer off myself?
However it turns out, thank you for getting me started!
Very cool! I do wonder if the required oscillator frequency related to the linewidth of the comb of modes in the cavity.
If you'd use would the AOM you have as a frequency shifter with a stationary mirror, would also work?
6:33 *Could this be used to produced pulsed laser, somehow?*
The speaker has to be still at it's max & min extension (when it switches direction), so at that point I assume the laser could become aligned (light is VERY fast) & can pass through a mirror that is filtered to let through a specific frequency?
Or something like that?
They are reflected back in on themselves, inside the device, that's how the laser amplification works 👌
(For those who didn't yet watch it)
Military flashlights, lazers & fuelless plasma torches are quality tools.
LED's have a tricky history even.
Why does the DOD patients office not like civil engineers so much? The reasons technology advancement information is getting blacked out is not likely from any of our own.
The military,
They are so anti-tool advancement in the scientific community!
It's not the users that are lead,
It's the tools that are dangerous.
Is the answer NOT to patent any advancement not intended for commercial purpose? I know there might be still some risk of IP seizure or restraint, but isn't the main way tech is bottled up via patent applications?
Interesting... Now I have to take a few different solid-state lasers and see what they can do to themselves and each other. What can go wrong?
I use it for Ramen analysis too.
I use mine for ramen noodles, but waving it back and forth across the pot fast enough, long enough, to cook the noodles tears up my wrist!
I've always wondered about that in particular. Guess you have the answer. My original hint of having the question was knowing the output couplers on them are a ridiculously high value (99% reflectivity for example) so at say 5mW that should translate to something like 500mW or half a watt of optical power intracavity. (I did some bad math and forgot to convert from percent to decimal when doing the ratio division to give the scale factor. This has been corrected though.)
completely noob with lasers here, is the output coupler a partial mirror?
Yes. Normally >90% reflectivity.
or in better lay-terms... the vibrating mirror creates a situation in which 99.9%+ of the power of the laser is sharing cavity with the active cavity but not at the same time... it is out of phase for all but a nearly infinitely small amount of time... creating a near infinite number of 5mw lasers that are out-of-phase with the main one that are regulated by angular loss.
Remember kids... light is neither a particle NOR a wave NOR DOES IT ACT LIKE EITHER... the thing that detects it is both vibrating and solid and thus those characteristics are imbued in its reaction.
Hi Les: Very interesting. The modulator here is a bit like an "Active Q-Switch" used in high Q lasers
Yeah I dont fully understand what is going on here.
When he first described it at the beginning, my first thought was, "oh, that's a Q-switch". The YAG units I worked with were much more efficient and IIRC they consisted of a solid crystal driven by an RF signal. It was easy to get a peak power of a couple hundred kilowatts from a 100 watt resonator, although of course the average power couldn't be more than what it would do in CW.
I don't think it's like a Q switch. Perhaps in effect, but not in principle. I've never played with a HeNe laser, but know that Nd:YAG lasers have an envelope of frequencies they'll accept ( individual nanometers wide ). I think this works by increasing the level of excited photons by driving the gain medium with more than one wavelength via doppler shifting.
Not sure I understand the purpose of the oscillator here - Does the cavity light come out modulated at the same frequency?
Maybe the OC on this tube has different reflectivity to a standard HeNe.
Wonder if this would work with yellow or green HeNe tubes.
The oscillator drive a piezo element with a mirror coating on it do decouple the external cavity. I have not measured the light output in the time domain, but I suspect there would be measurable ripple, but I also expect the laser linewidth would be broadened to some degree. There is a lot to investigate here, so example, what if the frequency is varied.
The OC will be difficult to measure in-situ, one thing of note, the radius of curvature on the OC is high enough to be noticeable by eye.
It will very possibly work with other tubes. I have a German made Green He-Ne and if you back reflect the beam into itself, it will also generate Red at 633.8nm at the same time. It would be interesting to see what happens to it.
That is really interesting thank you.
Thanks!
huh... thinking about it, what does the oscillator do really? and why do the frequency and distance to the output coupler matter?
If we vary these, can we get a cavity with peak power beyond the 1 watt range?
This is probably designed to produce the Maximum Q by the manufacturer, but there is a fair amount of experimentation that can be done here, including varying the frequency and perhaps even trying other mirrors as well.
The oscillator and piezo/speaker are constantly changing the external cavity length, the goal being to avoid feeding back too much energy into the HENE tube with a phase that would kill the lasing action. The frequency and amplitude fed to the piezo must be sufficient to give an adequate rate of change of cavity length to minimise the time spent with the external cavity feeding back energy into the laser tube with destructive phase.
Fourier Transformed IR and Dichroic mirrors give that a go and see what happens
If you wad the mirror on some rails and you could move it back and forward on the micron level could you move it so you get phase cancelation of the laser?
Welp, time to start another year long project
I wonder if the power is consistent through the entirety of the beam path. I do wonder if anything like standing waves would be a thing here?
Figured it was a Brewster window tube but this is way cooler!
Yay, a new video! 🤩
I see a lot of power in the passive chamber that is killed by everything done inside it while operating. How can useful power be extracted from this device, to do work after generation, especially continuous work? Have you tried splitting out half the power, for example, and does that shut down the boost, too?
Don't ever reflect a lazer beam unto itself, as it may open up an interdimensional portal allowing dogmen to enter into our reality. 🤔
Better dogmen than trumpists
Massive thanks to Sam Goldwasser and Don Klippstein for their contributions to hobby electronics. I remember using library computers & dialup internet in the early 2000s to save (to floppy disk), or print pertinent pages from their sites. I owe a lot of my understanding of lasers, optics, xenon strobes etc. to them!
Absolutely, I feel exactly the same. Giants of our time!
I would mount the cube dump on a Pizo Electric disk so it will be off-axis enough to block the cavity as you did with the card and sweep it through the audio spectrum so it will allow to Chirp the beam to pass, kinda like a poor-man AOM and see if it will kick out some huge power burst if you have a mind to investigate it, and maybe just use a cube beam splitter in there and dump part of it out. I would! but have not one of those laser tubes. :)
Light never ceases to amaze me. It does so many strange things.
Watching my laser engraver work is pretty amazing. Like I can cut into stone with it to engrave images onto stone using nothing more then photons
That particular speaker in the audio world would be called a "servo-driven speaker" as it appears in the patent to have a feedback coil in the speaker.
This is very interesting how this is setup.
I have a Small Yellow HeNe laser, and by reflecting the output back in on itself using another HeNe Mirror, I was able to cause the output to flip to Red 632.8nm..
One other thing I missed. I don't think Doppler shifting has as much to do with the external cavity gain as previously supposed though it might play a role. I think it might be a form of forced mode hoping so to speak. So you rapidly change the effective length of of the resonator the end result is a series of beat waves that are nearly full power with out it staying in that state for too long. It's like moving the slide on a whistle that is frequency stabilized at a stupidly high harmonic. So any gain will be alternating between full gain coupling and none. Hopefully someone will get around to testing that.
Interesting. Yeah, I plan to mount this on a rig and perform some measurements. I suspect line broadening must happen as well. I wonder if there are modern applications...
This is a whole field of research as far as sensing - optical feedback interferometry or self-mixing interferometry. Though not really done with gas lasers nowadays.
In the early 80's and I'm pretty sure it still applies, the collated beam would bounce from a 100% reflective mirror at one end of the laser, be it a CO2 gas tube or crystal rod like Nd YAG, to the partially reflective mirror at the other end as the intensity of the beam amplified before exiting the laser. Redirecting that beam back into the laser? Might result in additional amplification. Don't know. Never tried.
You need a powerful laser for ramen analysis?! I just use my sense of taste 😜
Is DIY Raman spectroscopy in any way achievable, do you think?
Try other wavelenth mirrors with it, maybe a yellow one if you got it. Adjust so the focus coincides. Also try adding a AOM and see if you can cavity dumo the light. Also they used the same trick here with argon lasers for medical gas analyzers in the 1990s. ❤
It would be worth a shot. I'm interested to try other piezo elements as well.
what would happen if there's no oscillator and the two regions are coupled?
I would love to see a video on building a Gamma Spectrometer. Using a photo diode to see individual photons of light flashes from a crystal that’s hit with gamma radiation is really cool.
Are there any tools to measure (not lab quality) the laser output that isn't $1000+? I've only started messing with lasers for fun but curious to know the true power output of what I've been playing with, I only know how to measure the electrical current but that doesn't really mean much as far as energy output.
From experience I can report: You'll have a high chance of converting a laser diode into an incandescent diode.
Fascinating
Did someone say lasers?
Kids today play with some stuff that was seriously expensive in my youth. It's a good thing though. Could you imagine ten year old me with a laser? Kids didn't get much supervision back then, and we were only partially domesticated. . .
I got my first He-Ne Surplus from a Laserdisc player, been hooked ever since. LOL partially domesticated :-D
Well considering I know that the eye doesn't dilate when a laser is pointed right into it, and that I know this without doing any online research, shows that it's probably good I didn't have access to more powerful lasers back then.
One of my Philips laserdisc tubes has an external mirror glued in place on the output ! Looks like a repair of some kind, maybe to "boost" output ?
That's weird. Is it a corrective of focussing optic?
@LesLaboratory maybe ? I have four in total and its just the one that has it ! It's bonded on at a 45 degree angle at the output end !
You destabilize the cavity, resulting in mode hopping and other funky stuff.
what "smoke" do you use?
Heated Glycerine, the same stuff that's in smoke machines. I used to use magican, but it makes an oily mess.
@@LesLaboratory I see, Im looking for an easy smoke or vapor source that can be used as a crude beamvisualizer at will and easy to store without to much degradation.
I saw some small almost carkey size devices that can make smoke that goes for around 50 bucks, but it does seem like its intended for magician, and if it makes an oily mess, that is far from ideal.
So im curious what other people in practise are using and the pro / cons of it..
Thx for another great vid Les.
you need the Deflektor chiptune soundtrack fo this video
The best part is to drop particles of diamonds into the laser and watch them float giving the tractor beam affect
Not quite on topic but I have an IOT device that incorporates the mandatory LED power indicator. The LED is a typical red 0602 size surface mount type. What makes it peculiar is that when it its on it is surrounded by a mist of red dots (interference pattern, I guess) that extends to at least 5mm from the source in all directions. I've never seen this before and it is only very recently that I have come across another example of this effect. I'm wondering if anyone can explain what's going on.
NGL, I still dont fully understand how this works to ramp up the power. I get the doppler shifting and all that but how is this thing working exactly?
Wouldn't this be pumped phase conjugation
Lasers are cool 😎
*How but not WHY - That is the problem with this video.* Sure, it goes into the 'how' of an extra cavity, but is that really an extension of the main cavity? Or is it merely a second cavity, in which the meager main output builds up to high power because it has no place else to go? And then, *why is it necessary to detune the second cavity* with a vibrating mirror?
@Les' Lab
It's still not clear to me how this works. Is the ~1W gain due to the arrangement “storing“ light in the passive space? i.e. the decoupled beam bounces back and forth, and builds up to 1W equilibrium after a short period of time?
Was wondering the same. In the primary cavity, the beam builds up optical power by repeatedly passing through the population inverted laser medium.
The beam can not pick up energy outside the primary cavity, because there is no laser medium.
But if the trick is that this secundary beam picks up energy if re-enters the primary cavity, it will still have to mode-compete with the primary beam. (partially deplete the population inversion)
I analyze my Ramen by taste instead. Love it with peas, carrots and a dash of soy sauce. 😂
Couldn't you get the same beam amplification effect by shining a laser into a high finesse fabry-perot cavity? The coherence length would need to be pretty high, though
That's how Teara-Watt Lasers work, Les. :) Try using a half-wave plate a quarter-wave plate or a combination with a polarizing plate Beamslitter cube and dump the cavity out of the PPate.
For example.
Plasma tube side *>>* Detector back reflector.
| |
| Polarizing plate Dump. Halfwave plate. |
| | Cube polarizing beam splitter Dump. | |
| | | Quater wave plate. if you like | | |
| V v v v |
M3 \\----\*\-----------------[ * ]--------------------------------------------*------------------------------[]---------[]-------------// M4
Basically they glued a mirror onto a speaker like I have done as a kid.
I used to troll thrift stores in the 80s looking for Philips LaserDisc players.....
In the 90's and early 2000's, those Lasers turned up at surplus stores real cheap, but you can hardly get them now, and when they show up they are $$$
Same. Edmund Scientific & Spectra Physics were my "dealers" for gas lasers. Good times.
First gen laser copier optics decks with HeNe tube and supply, scanning mirror, and AO modulator were cheap and plentiful on the surplus market in the early '90s.
With a blue laser it burns them out. And or melts the lens then that contains the heat and burns it out.
thats the beginning of constructing a real lightsaber.. like a reverse power coupling!!!
I have three of them that I'm still using now and then :p 8mW, so not powerful at all, and unfortunately I only have 2 power supplies. But they're really fun to play with ;) (the simple ones, without external feedback...)
Nice, these things are as common as hens teeth. They rarely show up at all anymore.
Converting electrons into photons or emerging them out of the ether that's already there?
Did I miss it, or did you miss it?
The external cavity does not have a lasing medium, so it can not generate the exta gain (power) available in the the external cavity.
Does that mean all the extra available power comes from the extra passes the light makes through the primary cavity?
And how can it do that without mode-competition with the standing wave in the primary cavity?
The external cavity is entirely passive, and has no gain. It effectively decouples some of the intracavity light out in to the passive cavity. The mode competition is handed by the rapid movement of the mirror on the z axis.
@@LesLaboratory Thank you for taking time to reply.
I had expected that the vibration takes care of the mode competition (in the sense that it does not generate it's own standing wave) but there is still depletion of the population inversion in the primary cavity.
The coherence of the beam in the secundary cavity is probably not great.
Thanks for the video. It's very interesting stuff.
10:26 Isn't a square wave just about the worst signal to use in this application, considering it spends a lot of time at a constant voltage (i.e. no movement of the mirror hence no doppler shift). It might be interesting to see if using a triangular wave makes a difference.
Likely the voltage swaps before the transformer is saturated. I believe switchmode power supplies feed the transformers with square waves too.
I don't get it. It is no harder to mount & seal Brewster window to laser tube than a mirror. If Brewster window leaks, why not mirror? Furthermore, a scheme of "hard sealing" both mirrors & windows was developed. I have rescued many of these epoxy-sealed tubes by re-firing the getter followed by helium soak. Some epoxy sealed tubes beat all odds & last over 40 years. I have SP-124 lasers that are still working presently.
I say that the REAL reason for this scheme is that it can be used with COMMONLY MADE laser tubes. As soon as you put Brewster window on, you open a mechanical can of worms, demanding a structure external to the glass of the tube to hold everything in alignment.
For really long laser tubes (like SP125 laser), I have seen the discharge current disrupted by reflecting the output back into the laser.
How are the mirrors aligned on integral-mirror laser tubes?
So the frequency doesn't need to be 'tuned' at all as there's no adjustment if you did have a pot on there to tweak could it improved any or is it not overly important please ?.... Sensational colour even on my monitor must be awesome in the lab.........cheers !!
The only requirement seem to be that it's fast enough. There is no pot, but I could try it on a signal generator, and sweep it from 1Hz to 500kHz and see what it does 😉 I wonder if there is a modern use for this effect. He-Ne beams are always beautiful, fire nicer than any Laser Diode. Cheers!
@@LesLaboratory Yep:)
I wish AS make video on same topic.
I am confused - where is the mirror? And what happens?
Given 1-watt is trivial for a laser diode, why screw with this?
In the 1980's, there were no one watt Laser diodes. In the present day, well something new could be learned from something old.
Doing it with a HeNe is more of a proof-of-concept demonstration - it's much more practical when applied to other kinds of lasers. It probably wouldn't be difficult to extract a peak power of a million watts from a 500 watt YAG/YLF/whatever at around 1064 nm, which is extremely useful for cutting and engraving different kinds of metals.
We use these lasers to align hifh powered CO2 lasers and the Nitrogen lasers. Quite useful in working the Nitrogen laser. Quantum optics is interesting.
I use tape to align a CO2 laser
Would not it affect the breaking of the cavity amplification Process if you interact with the beam inside! then how it's even possible to use that beam?
As happened here 11:36
This is what is special about this, this is an extracavity design, so a regular He-Ne laser with a third mirror. In a Brewster windowed tube, Lasing would cease entirely.
Weak or not, it still looks great.
i'm surprised the "1 watt" is available outside the oscillating cavity. These lasers are extremely difficult to get to lase. I would expect any scheme to divert energy would make it stop lasing.
It's pretty weird. The catch is, you can't get the 1 Watt out of the cavity, it's just trapped in there. the moment you try to couple light out, you are back down to fractions of a percent of what is available in the cavity.
I have a HeNe laser that produces 30mW red output beam, it’s over 600 mm long.
Sweeeeeet! I see them on eBay occasionally, but don't have the space!
I have one like that, Siemens LGK 7626. Still going strong 40 years later! Diodes are amazing, but hard to beat the beam profile of an old-school gas laser. Besides, 633nm is the best color ever.
We all time traveled ten seconds into the past
I met Sam from Sam's lasers personally.
Nice! I have collaborated on stuff for the FAQ with him. Great guy.
@@LesLaboratory He was visitor once every while (he was often invited) to Laser Teaching Center at physics department at Stony Brook University. That's where I met him. He gave mini colloquia once every while. :)
Ray says it's really bad if you cross the beams....
How bad? 😉
I'd risk it if I had no other way to roast marshmallows.
Bob, it's just you again. Tell me more details or what reality is about
The laser takes a screenshot
take it up to 100 giggawatts
Hydrogen neutron Lazer ?
So, what happens when you do this with a modern high-power Lazer that will fry your eyeholes in an instant?
now i'm wondering if I can do this with my 150W laser
And with a chemical laser?