INSIDE A LASER! An Open Cavity Helium-Neon Laser!

Рет қаралды 8,825

Күн бұрын

Episode 64
#laser
#electronicscreators
Let's take a look at an awesome open resonator cavity He-Ne Laser!
Tweak-able and hackable, you could fit your entire body inside the Laser cavity!
I talk about the Brewster angle, and the technical specs of a NOS Brewster windowed Helium Neon Laser tube!
Optical contacting is discussed, that is used to bond glass parts with no glue, but creates a permanent bond.
I designed built a really cool mirror mount that can hold 6 Laser mirrors!
I show how to do Quick and Easy Laser alignment, and demonstrate Transverse Electromagnetic Modes (TEM), as well as extend the cavity to around two feet!
Brewster Laser tubes available from:
www.ebay.com/itm/303507585770
RP-Photonics Encyclopedia
www.rp-photonics.com/encyclop...
Sam's Laser FAQ: Care and Feeding of the One-Brewster HeNe Laser Tube
www.repairfaq.org/sam/onebrew...
Sam's Laser FAQ: Mirror Mounts
www.repairfaq.org/sam/lasercl...
Check out my other videos: / leslaboratory
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0:00 Intro
0:08 Laser tubes
1:04 Brewster Windows
1:38 Brewster Laser Tube
3:02 Optical Contacting
3:28 Mirrors
4:11 Tube mounting
5:02 Mirrors
5:33 An AWESOME mirror mount!
7:37 Tube lit
7:57 QUICK and EASY Laser Alignment
9:25 First Light!
9:55 Rotating the Mirrors!
10:39 The output beam, beautiful modes!
12:30 Half metre cavity!
13:00 Smoke test
13:19 Out

Пікірлер: 103

@DUIofPhysics 16 күн бұрын

That moment when the laser suddenly starts to lase during alignment is incredibly satisfying!

@LesLaboratory 16 күн бұрын

Ooooooh yeah!

@robertbass4590 15 күн бұрын

I couldn't agree more. Decades ago I saw my first laser and I believe I react the same way seeing these videos as I did then. It's almost like watching magic, even thought I know exactly how the trick is done. It doesn't get old. Les is living my best life, I think.

@paulmcgrath2175 11 күн бұрын

Been there, had bought a small argon tube from ebay. Was a gamble as it was sold as gas intact but no output. I believed the output would be green, I was right.

@WoodenWeaponry 6 күн бұрын

Totally agree!

@Muonium1 16 күн бұрын

Exceptional demo of the different modes. Very rare to see demonstrated.

@IAm18PercentCarbon 13 күн бұрын

This was an amazing video to show modes, specifically, as well as demonstrating how spontaneous and fickle the population inversion/lasing state is, even with nearly-static conditions. Really earning the "S" in laser.

@TheTablet314 15 күн бұрын

Small Video Idea: Since you can make the cavity is so short, you can have probably enough longitidual mode spacing to operate the laser with just a single longitidinal mode. Since you have fiber coupling materials and experience, you could make a video on actually measuring the coherence length by interferometry by fiber coupling one arm to a long fiber. Or you could go more into depth by showing some techniques to measure laser linewidth of very narrowband lasers.

@LesLaboratory 15 күн бұрын

Agreed, I think playing with longitudinal modes could be very interesting. There is so much to play around with here.

@bpark10001 15 күн бұрын

What you need now is a set of mirrors to get 610nm orange, 594nm yellow. I have such sets of mirrors for Spectra-Physics 124 laser (2 foot cavity, 15mW output @ 630nm, TEM00 with stock mirrors). Particle measurement systems gave me the mirrors when I promised to report the power output. I got 7mW @ 610,nm, 4mW @ 594nm.

@shadowshadow2724 15 күн бұрын

When the laser started lasing , it felt magical.

@stevehill5913 16 күн бұрын

Most excellent work in Les' Lab. Now, with a pinhole and acoustic modulator, you could active Qswitch or try cavity dumping. Keep up the great work.

@dalenassar9152 16 күн бұрын

This video was breathtaking! Very nice six-shooter. I was always fascinated by a brewster window HeNe laser...finally got one cheap on ebay. It did not lase at first, but I found that if I put a little hand pressure on it, it would start to work...finally it stayed on. I could see two reflections on the ceiling from the brewster windows. The output beams from the ends were polarized (as expected). I did feel a little un-easy at the beginning of the video...I would have worn surgical gloves with fingers so close to the mirrors. When you showed particles of smoke killing the beam, it reminded me of a project I was hired to do (we called it a 'foam detector'), that would trigger if anything got in the air above a flowing liquid. I finally found the answer in using two optical fibers spaced over the liquid: one fed with a red LED (this was before bright LED's!!) and the other with a phototransistor...with a comparater circuit at the detector end. This arrangement would also trigger on a thin layer of smoke between the fiber ends. The trick was no-focusing at the open-ended fibers. Despite elaborate setups first tried. ...sorry for the ramble, but brought some back good ol' memories!! THANKS MUCH!! --daLe

@LesLaboratory 16 күн бұрын

Thanks! I'm going to have to get hold of a longer tube, but I will be waiting a loooong time I think! I have no fear, but yeah, gloves would be a good idea! Yeah its pretty cool to see it wink out. Sounds interesting, never considered detecting foam, but I am sure there are situations where that is an absolute requirement. At the moment I am working on a project that is very sensitive to dust, it might be interesting to detect that at an air-water interface.

@dalenassar9152 16 күн бұрын

@@LesLaboratory Sounds like a "Snell's Law" app. and yeah...the foam-detector was a VERY big deal for this medical company (Dynatech Precision Sampling). It was worth a lot to them, but I worked in my offsite lab, and was paid based on the 'part's list' value....really felt ripped off...learned a lesson on that one...draw up a contract! I saw a very long, ~3 ft, beautiful brewster laser at the university optics lab during a tour I got for my 10th grade science project (holography)...ended up going there in physics where I earned my degree and taught for 7 years...that laser was still there untouched probably since the 60's. I was in good standing with the dept. and some years later ALMOST got it! They were ready to let it go, but opened the case and saw it was tagged :(

@dalenassar9152 16 күн бұрын

@@LesLaboratory Perhaps a Snell's Law / scattering /polarization app.

@dalenassar9152 14 күн бұрын

@@LesLaboratory Les, When winking the laser off, at the VERY threshold, does it go fully off immediately at 'wink-off' attenuation?...any jitter? IOW, is it tripped by just blocking a few photons? If so, it would also be very interesting to know if there is any "photon" hysteresis...if so, probably a very difficult determination.

@LesLaboratory 13 күн бұрын

It would be interesting to measure it, surely it is possible!

@MrJimmyjammmy 15 күн бұрын

That whole alignment process reminds me very much of collimating my reflecting telescope, very similar principle.

@Farathus 12 күн бұрын

Very sweet Multimode hoping going on! I love playing with these. The coolest i had seen so far was a regenerative amplifier using a misaligned seed laser and very few amplification cycles. When using a very low number of bounces the output was highly multimodal and with every additional bounce the number of modes would reduce until eventually at about 10 round-trips the output was a nice gaussian beam. Survival of the fittest at its finest! At certain points the output was jumping back and forth between two different sets of modes. Super cool phenomenon.

@LesLaboratory 10 күн бұрын

Sweet! Sounds really cool!

@nomcopterlabs 15 күн бұрын

Wow the modes really are beautiful. Instantly reminded me of electron orbitals!

@LesLaboratory 15 күн бұрын

They sure are. Yeah that seems to be a common thought. The distribution of light in the modes is probabilistic, not unlike the electron orbital diagrams.

@christopherleubner6633 15 күн бұрын

That's exactly what they are. Transverse Electric Modes. The quantum effects get amplified to a macro scale. ❤

@massimocappello5619 7 күн бұрын

Great way to get alignment! 👏👏👏

@LesLaboratory 5 күн бұрын

Thanks! With one mirror this is pretty straightforward. It is possible with these (I have heard) to hold a mirror in your hand and get it to lase albeit briefly!

@LateralThinkerer 12 күн бұрын

Wow. Just wow. Well done!! As far as a detent on the mirror holder, it might make more sense to have alignment marks instead so you're not fighting any misalignment from the spring-loaded tooth/lever.

@LesLaboratory 12 күн бұрын

@@LateralThinkerer Thanks! Yep, you are right, the more I have used it, the less inclined I am to implement detents. Marks are a good compromise.

@harriehausenman8623 13 күн бұрын

WOW! 😲 I was in awe the whole video, but the modes really got me. Such beauty. Thank you so much for showing this 🙏

@LesLaboratory 13 күн бұрын

You are very welcome!

@Matthew.Morycinski 15 күн бұрын

12:00 There are laser models where an intra-cavity diaphragm allows for changing from multi-mode to single-mode operation.

@CarletonTorpin 16 күн бұрын

11:30 - It looks like mitosis for photons!

@rkirke1 11 күн бұрын

As a biologist I thought the same thing. Also reminded me of the different electron cloud configurations around atomic nuclei.

@andymouse 15 күн бұрын

Awesome ! watching the mode change was fascinating...cheers !

@LesLaboratory 15 күн бұрын

Thanks! Pretty cool stuff! :-)

@ProjectPhysX 15 күн бұрын

In the laser practical course at university, we put a hair in the HeNe laser beam to trigger it switch into different modes. It was really strange and fascinating to see a donut or gummy bear shaped laser spot on the wall instead of the regular dot I was used to.

@LesLaboratory 15 күн бұрын

Yep you can force TEM01 with a hair, I should have done it! Plenty more to play aroynd with.

@senorjp21 16 күн бұрын

Wow never saw a demonstration like this before. I don't think I've ever seen the alignment process "switch on" like that

@LesLaboratory 15 күн бұрын

Thanks! It is way cool!

@MathewMoss-fp9ju 15 күн бұрын

Love this I have a nostalgia for old cathode ray lasers, I a dilemma with a recent project I placed my green 515nm laser into my flipper to the GPIO ports but when I switched on the laser it was very dim compared to the 405nm 150mw laser, I'm based in Manchester I like playing with lasers and projects I'd love to make a gadget that laser based and have perhaps a upgrade that runs data uplinks and downloads and stream FTL communication, not that I'd know how to build a system of that grade

@barrieshepherd7694 14 күн бұрын

Kudos for your lath skills 😎. The rest is pretty good as well LOL

@LesLaboratory 14 күн бұрын

Thanks I'm pretty pleased with how it turned out. It's amazing whatvyou can make on a cheap hobby lathe!

@doug694 15 күн бұрын

I didn't know Sam had an eBay shop :o (I used to contribute to his laser FAQ, years ago!). Anyway this looks really nice. I was lucky to pick up 3 tiny HeNe tubes (red, yellow, green) when these things were a bit less rare. They produce similar multimode patterns which shift continuously over time, cool to look at especially when the beam is expanded onto a wall. I need to dig them back out again...

@LesLaboratory 13 күн бұрын

Ah, I had those exect same tubes years ago, but I had to sell them. Hard times 😔 Little cute tubes in plexiglass outer tubes mine were. Yeah, I found siliconsam a while back. Cool, I contributed to the FAQ too (Cheap Blu Ray diode discovery reverse engineering)

@doug694 13 күн бұрын

@@LesLaboratory that's interesting... yes plexi tubes with tiny potted brick supplies🤔I wonder if I actually got them from you? I contributed to the SS lasers area (ruby & yag) & power supplies.

@LesLaboratory 13 күн бұрын

@@doug694 Who knows, it's a shame they don't still make them, but it's not like there is a shortage of wavelengths these days. Nice! I have spent a good portion of my life poring over the LaserFAQ!

@tizwah 9 күн бұрын

The modes look like patterns on a Chladni plate.

@2smoker64 16 күн бұрын

I had an old argon laser when I was a kid with external mirrors; always wanted a hene, so cool🤘 See if you can pull a green 543nm beam out of it

@RingingResonance 16 күн бұрын

I was going to suggest the same thing! Would this be a matter of changing the distance of the mirrors slightly until the beam turns green?

@LesLaboratory 16 күн бұрын

I could try other mirrors, but this is a very short tube, and there is no way to change out the high reflector. It would be interesting to see if there are other wavelengths present though.

@RingingResonance 16 күн бұрын

@@LesLaboratory Ah, so the type of mirror does matter. I had a feeling that these mirrors were also tuned to the frequency of desired light output while passing as much as of other wavelengths to minimize lasing at other frequencies in order to increase efficiency. You might try a high-reflective lens for green lasers and expect the beam to come out of the other side as it's technically the low reflective mirror for 543nm.

@TheTablet314 15 күн бұрын

@@LesLaboratory 635, 629 and 640 are probably within reach of the high reflector. Maybe a 3 element cavity with a brewster prism could be the filter to cut out the main line.

@LesLaboratory 15 күн бұрын

@@TheTablet314 probably. I have seen the Raman line at 650nm pop up in most He-Ne's as well.

@yourfavouriteta 15 күн бұрын

Beautiful work!

@LesLaboratory 13 күн бұрын

Thanks!

@thevoidedwarranty 15 күн бұрын

Very fun & entertaining video for me cause i donno much about optics or lasers .

@WaffleStaffel 15 күн бұрын

_Wow_ Fascinating!

@ozzymandius666 16 күн бұрын

Fascinating! Those modes make me think of the shapes of atomic orbitals, for some reason. A couple of questions: Does that optical bonding technique actually stop all helium diffusion, or at least as much as the glass itself does? The laser consumes around 230 watts of power, how efficient is it?

@LesLaboratory 16 күн бұрын

They do indeed, never thought of it like that. Yes optical contacting is as leak proof as the rest of the glass. Once the bond is made, the pieces cannot be separated without cracking them. 720v at 3mA would be about 2.16 watts of electrical power. The tube is rated for 1.3mW out so around 0.06% efficiency. The intracavity beam however is constantly circulating and could be a watt or more. I am going to look into a way of actually measuring this circulating power.

@ozzymandius666 16 күн бұрын

@@LesLaboratory Thank you! D'oh. I misunderstood 3mA for 300.

@ericwazhung 16 күн бұрын

Atomic orbitals was my thought, as well. And, frankly, I'd think the reasoning/math behind the two are very similar (albeit one in 2D and the other in 3)...

@ozzymandius666 16 күн бұрын

@@ericwazhung Hmmm, I wonder if the excitation modes can be made to vary with time, so you get a 3D pattern...or if they already vary with time, and what we're seeing is an averaging...I'd like to know the detailed physics of how the modes actually work.

@WaffleStaffel 15 күн бұрын

There are videos on YT where you can see the interference pattern change as it bonds together. It's fascinating!

@mehamrdio6173 15 күн бұрын

Thanks!

@LesLaboratory 15 күн бұрын

Thanks for your support!

@r100curtaincall 3 күн бұрын

Very nice I considered asking Sam for one of these a while back but I have a larger 580 so I don’t really have a need for the 564… gotta admit they’re cute little things though! Always fun to see extra cavity beams. You might consider getting yourself a littrow prism and then you’ll be able to make any of the colors individually, provided the losses aren’t too great.

@LesLaboratory 20 сағат бұрын

Cool! wish I had the Larger tube but it was stretching my budget! I think the losses in this little tube would be too high, but it would be interesting to experiment with it.

@r100curtaincall 15 сағат бұрын

@@LesLaboratory it very much works. I do it all the time it just would have to be of a reasonable quality. The high Q mirror also likely generates many wavelengths. If you have a diffraction grating you will likely get a decent spread.

@flaviospedalieri8707 15 күн бұрын

Very nice job on the mirror selector. I do have one of those tubes, sadly it’s high mileage. However, I do have an SP127… pushes over 42mW

@LesLaboratory 15 күн бұрын

Thanks, I'm pretty pleased with it. Sweet, I would love to see a tube like that!

@Brandon-rc9vp 13 күн бұрын

I alwys get exited by videos by you and huygens optics!

@LesLaboratory 13 күн бұрын

@@Brandon-rc9vp Thanks! I'm glad you like these. Yeah I watch Huygens Optics as well, it's all great stuff on there!

@fzigunov 16 күн бұрын

Have you managed to get a DIY pockels cell out of those in-house KDP crystals??

@LesLaboratory 15 күн бұрын

It's definitely coming! I have been working on growing sufficiently large and clear crystals to cut and polish. Results are promising, but I want it just perfect :-)

@Zenodilodon 9 күн бұрын

You say that having flat output windows that reflects up to 4% of the light would make lasing impossible. That's clearly not accurate as you and I have changed the color of helium neon lasers that have flat fritted OCs/HRs with external optics. If flat optics made lasing impossible than we couldn't do that. From what I know the main use of the Brewster window is to polarize the laser beam. Very good video and smart idea with the optical carriage! Those modes are incredible :P

@LesLaboratory 9 күн бұрын

@@Zenodilodon It's more nuanced than that, its about losses. He-Ne lasers have terrible gain. I supposed if you precisely reflected that 4% light back into the cavity, you could have it contribute to gain, but that plus the mirrors gives you four (six including the opposite sides of the windows) surfaces you now have to align. At best it would be very unstable and at worst no Lasing. In total the losses would have to be well under 1% to work. With one external mirror, we only have one surface to align, and even then stability is poor. Yep, those modes sure are pretty!

@Zenodilodon 8 күн бұрын

@@LesLaboratory So I decided to play around with my yellow He-Ne last night and I set it into doing reds/oranges with an external optic and did some messing about. So I stuck some microscope slides in the resonator path and found out a few things. Yes the Brewster angle does offer a good stable and predictable pass through angle, but it didn't seem to be that much more efficient overall. I was able to get lasing with 2-3 slides in the beam path however with diminishing returns with each slide. The interesting bit came into play though where the the beam would flicker through the colors as I changed the slides angle, actually it even looked like some beams where more yellow, and some where more red, it's very hard to explain or even photograph though. My guess is that it's acting like a BRF or Etalon. While I didn't see much change in lasing efficiency all to much I certainly saw where instability could be an issue. As long as the tube's bore window was planner and aligned it would be fine, but the brewster angle is an ideal best case for an external cavity laser. However a brewster window is used in sealed fritted He-Nes and even ND:YAG for polarization purposes only. Flat tube windows do not make lasing impossible, doesn't even seem to make it that much more inefficient. Please do replicate my setup, It's neat playing around with the microscope slide as you can actually use it to make an easy somewhat tunable He-Ne it looks like!

@RoosieBoomstick 14 күн бұрын

Plain glass will reflect 2 Fresnel reflections, or 2x4=8%😮

@wayneeligur7586 16 күн бұрын

I read that a pure 'neon based' laser if constructed, would be much more efficient and powerful, so why did this He-Ne type dominate, with the other forgotten; could one build such a laser?

@HuygensOptics 15 күн бұрын

It's actually the other way around. The presence of Helium in the mixture increases efficiency and stability of operation.

@wayneeligur7586 15 күн бұрын

@@HuygensOptics I read this from the CRC Chemical Handbook actually awhile ago, yes to your point, yet they also cited this and said pure neon was more efficient

@LesLaboratory 15 күн бұрын

Pulsed Neon maybe. You can dump nanosecond high voltage pulses through Pure Neon and it will Lase on a couple of odd lines. I am not sure of the efficiency, but even if it is good on paper, I would expect micro-joules per pulse out of such a setup.

@wayneeligur7586 15 күн бұрын

@@LesLaboratory Sam's Lasers had a long coherence length laser and variable computer controlled O.C. mirror but it looked too complicated; he was calling it a instead, a 'coherence moment' which makes sense after a long reasoning. As an element, Ne has emission lines and other desirable characteristics as a stand alone gas, this edition was from maybe the 80's. Under some pressure also.

@teresashinkansen9402 10 күн бұрын

Ignoring damage to the tube, does increasing current lowers the Q needed for lasing?

@LesLaboratory 10 күн бұрын

Unfortunately not. You night get a very tiny increase in output power, but these things are already optimized in terms of tube current and voltage. Argon Ion Lasers on the other hand will produce more and more light output as you crank the current up (until it melts of course! )

@Woloszow 12 күн бұрын

I wonder if Hydroxide-Assisted Bonding would be good enough for helium tightness

@LesLaboratory 10 күн бұрын

Interesting, I just read the article from JPL. Well optical contacting is Helium-proof (as far as any glass can be). I don't know about Hydroxide assisted bonding the article doesn't way what the process is doing at the chemical.physical level.

@raymitchell9736 12 күн бұрын

I have 2 He-Ne tubes that need to be recharged... they are encased in metal tubes... if you want them, you can have them (free, just help with shipping) contact me... At some point I will just throw them out. One of them is 6.9 mW was quite bright.

@portblock 13 күн бұрын

Im just a CO2 laser guy so a lot of this is above my understanding, and I have a question, if a gas laser has these brewster windows at both ends, could you put these lasers in series and intensify the beam? And just for curiosity, would a magnet have any influence on the beam?

@LesLaboratory 13 күн бұрын

@@portblock yes, you can series such tubes up like that. Some large industrial CO2 laser tubes are seriesed up to reduce the footprint. Magnets are sometimes used in large He-Ne lasers to force them to lase in the visible. You can do other stuff as well such as altering the polarization, stabilization etc

@portblock 13 күн бұрын

@@LesLaboratory Thats awesome! ok, one last dumb question and I wont pester you anymore.... Is it possible to series up different types of lasers? I assume one might get multiple wavelengths, and not sure but in radio waves we can get the sum and differnce of waves too - you sir are resparking my interest in lasers

@mikestewart4752 16 күн бұрын

11:51 mmmmm, Donut Mode…. 🤤

@brandon_bates 13 күн бұрын

Can you get another brewster window laser tube and do a double cavity laser for more power?

@LesLaboratory 13 күн бұрын

yes, you can double the intracavity power this way. I dont have the money for another one though, they are not cheap!

@brandon_bates 13 күн бұрын

@@LesLaboratory if you still have that other open cavity laser, could you use mirror at a right angle to marry the two or does the right angle mirror introduce problems?