Pulsed Laser Power measurement with Energy Sensors!
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- Опубліковано 8 вер 2024
- Episode 19
#laser
#electronics
#measurement
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Time for some Science! In this video, I measure the power output of my home made Nitrogen Lasers using Gentec Pyroelectric Energy Sensors!
Spoiler alert, I debut my largest home made TEA Nitrogen in this episode as well. What is its peak power? Watch the video to find out!
Gentec Catalog with how to perform measurements (page 13) : www.gentec-eo....
Gentec Catalog ED-100 (Page 32) : www.tsukasa-tec...
The code for the Laser energy Calculator is at:
github.com/les...
#laser
#optics
This is fantastic ! some great numbers, I love test and measurement stuff and lasers, so you work is fascinating...cheers.
Thanks. I don't think any regular folk have really characterized home made TEA Lasers before. At some point I will write all this stuff up and stick it on GitHub or something.
@@LesLaboratory Can't wait !
Ha, Lissajous on screen, just like in Star Trek. When can we expect a video on photon torpedoes?
LOL couldn't resist! Now there is an idea! :-D
I discovered your channel via a hackaday mention, and am really happy i did. Thanks for the excellent content!
Thanks! You are welcome!
I have heard of a threshold for opto electrical breakdown of air at 2GW/cm². So if you have apowr of a few 100kW this should be quite easy to obtain with suitable lens. It would be really nice if you could try this. I have it seen once in a laser lab with an excimer laser. nice sparks in mid air without electrodes
Funny you should mention that. A little side project I have been working on is rebuilding a YAG power supply I built almost a decade ago. When it is running it will easily cause air breakdown, and as you say it is spectacular to see. Stay tuned!
This is a fascinating experiment.
For low-power lasers, KTP crystals are the best choice for double frequency crystals. For medium-high power lasers, BBO crystals or LBO crystals from CRYSMIT should be better choices.
Interesting, I will look them up.
Have you tried having the spark gap closer to one end and having the electron pulse run down the length of the lasing cavity? I seem to remember Stong mentioning this as one method of using a longer cavity and increasing the gain without the use of a mirror..
I have not done this yet, but it is on my to-do list along with funky peaking cap geometries. There are a few academic papers that also seem to suggest you can get the discharge to travel with the pulse somewhat, though it is non trivial. Still, it will be interesting to play about with and there is of course the lure of extracting a Megawatt from this thing ;-)
A long time ago in universe far away, they did that in Scientific American using a meter (iirc) long chamber and a water aspirator for a slight vacuum. The cap was copper foil laminating a plastic plate and they set the lasing arc by discharging it at a corner of the PCB to try to get the inductance of the large plate in line with the lasing area.
Is there any way you can verify the pulse width? In my experience I think that your time scale is off by a bit. A Nitrogen laser generally has a pulse width of 30 to 70 nanoseconds. A spark gap can have a rise time of as little as 1 ns, but the pulse is generally controlled by the capacitance and inductance of the setup. So the current can flow for up to 100ns. The meta-stable transition of the Nitrogen molecule makes it impossible for you to get an other shot in less than 5 to 8 microseconds. The transition that gives light is 40 to 70 ns, that takes you to the meta-stable state which can take up to 5 to 8 microseconds to decay from. You reference a N2 laser you bought and talk about picoseconds, which means the laser is probably Q-switched which cuts the pulse width considerably. I built a N2 laser in 1976 at ASU as a part of a advanced physics lab. Spent quite a bit of time looking at scientific papers. Hint, to increase power, add some helium. The same setup also works with Neon which gives a green beam, but at much lower pressure (40 torr).
The lifetime of the upper Laser is highly dependent on pressure. A low pressure Nitrogen Laser may have pulse widths in excess of 20ns, however, as you increase pressure, the upper level lifetime decreases. As a consequence, TEA N2 Lasers running at atmospheric pressure, have pulse widths of
@@LesLaboratory what kind of speed would you need?
I have mountains of test equipment, a lot of which isn’t in use… But if you keep an eye on government auctions and auctions that take place at colleges and elsewhere in academia… you will constantly see extremely high end equipment very cheaply.
It’s not always the most modern stuff. But having an older analog oscilloscope with a 500mhz 1gs/sec bandwidth, is better than A 100MHz modern scope!!! And obviously they are easier to work on and calibrate.
I regularly see 500 MHz tektronix and HP scopes on eBay cheaply. And I’m pretty sure you can get scopes from the 80s and 90s with up to a 1GHz bandwidth…
I look at this completed eBay item.
294278851532
A 1 GHz four channel storage oscilloscope for $200?! Probably wouldn’t be the most easy to use and intuitive scope… But you can always keep your more modern scope for every day use… And only use this when needing the faster speed.
I have several lecroy scopes that I’ve kept over the years. Simply because they function properly and because they are extremely high bandwidth. And not worth selling. They don’t bring enough $ to part with.
What kind of speeds would you need? Not only To be useful now but far into the future with your other experiments.
@@LesLaboratory Really 800ns or 800ps
11:55 you can turn on averaging in the scope to or lower the bandwidth to filter out the noise.
Bandwidth limit is on and boxcar averaging used. The EMP from the discharge is pretty intense, and gets in anyway. At higher powers you come out of the noise floor a bit. The real way to solve this would be to case up the Nitrogen Laser properly. In commercial designs, they go nuts with their shielding. I probably should too.
@@LesLaboratory would be interesting to see how well a Faraday cage of sorts (let's say cardboard box covered with tin foil) would shield from the EMI, and if containing the EMI in the cavity with the laser affects its operation in any way (stability, power).
I wonder if one bank of capacitors could power an array of emitters. What do you think? I'd like to try it!
you could try limiting channel1 to 20mhz (should be an option in the channel menu) or add a external low-pass filter
This is with the BW limit turned on. The pulse these things emit is large enough to bypass the limiting. The ony solution here would either be to put these N2 Lasers in Metal cases, or use a Farady cage.
12:55 - couldn't you use CH2 as a antenna to capture the interference and subtract it from your CH1?
This should leave you with your signal right? Basically noise canceling the room.
Great Idea, I hadn't considered at at the time!
That would not work. In test with fast switching from only 8V to 30V, though with much higher capacitance of 100 micro F, so much slower time scale I had disturbances on both channels, which were partially up to 180 deg out of phase. I had to twist the two probe leads to at least have the induced signal in phase. I could not think about cancellation in any way.
Awesome work!
Thanks Ben!
@@LesLaboratory I just picked up the same sensor off eBay - should we have a challenge for peak power? :)
@@wrcman555 Go for it! The literature says it is possible to get a Megawatt out of a 30cm channel! There will be a lot of fiddling to get there though :-)
What laser goggles do you use and are laser goggles from survivallaser good? becouse the goggles from there are alot cheaper than others
For Nitrogen Lasers ordinary polycarbonate safety glasses will do! There are opaque at this wavelength. For everything else, you must use proper eyewear! I know it is expensive, but imagine you were blind, then ask how much money would you be prepared to spend to see again. Suddenly dropping 200+ bucks on a decent branded pair, doesn't seem all that bad!
@@LesLaboratory thank for the advise and i dit not know that just standard polycarbonate goggles whil do i am very happy about that
@@raulperez5697 Just make sure to get the wraparound style or the type with side protection, it's easy to get an unexpected reflection that catches you off guard
@@cambridgemart2075 thanks i already had polycarbonate goggles with side protection but stil thanks
@@LesLaboratory Like you I'm red/green colour blind. Something I've wondered is if Encroma glasses would make good laser goggles, as they have notch filters, and evolved from laser goggles for surgeons. enchroma.com/pages/about-us
They do "fitover" goggles: enchroma.com/collections/all#fitover
Would a rear mirror improve output on the big laser?
Yes it does. It has a rear mirror installed. It just doesn't increase the output as much as it does with smaller versions.
I bet the reason I cannot find the ED-100A on ebay is due to this video! I can't find the maximum pulse rate this unit is specified to be accurate at, does anyone know?
I can’t seem to find one of these sensors for sale anywhere. Even looking through the eBay completed listings…
Weird! eBay's search has been a bit odd lately, the algorithm keeps "removing results" for me. The seller id was: gucio25. There are a few Gentec heads on just now, but they are the larger Joule meters.
"If you look up in the literature..." Do have any recommendations for free, online TEA literature?
Yes there is an interesting paper here " Theoretical model of TEA nitrogen laser excited by electric discharge. Part 3. Construction and the preliminary results of the experimental setup examination" Here is the link: opticaapplicata.pwr.edu.pl/files/pdf/1993/no4/optappl_2304p217.pdf There are other as well. I have over 40 odd good references. I keep meaning to compile them in to a Literature review. I will get round to it when I have time.
Just found your site. Great work, thanks for sharing with us. Did you test the need for the mirror at the end? I think adjustments needed for the mirror could be hard for most. Does it double the power or varies nonlinearly?
It more than doubles the output. Adjustment with these is far easier than with other types of laser.
the sensor is agnostic to wavelength?
Yes, the black ones have a flat response from the UV to the far IR. The large white sensor is only responsive in the IR.
@@LesLaboratory hmm since photovoltaics usually work on a per-photon basis, how does this measure the energy rather than number of photons?
@@nicktohzyu they contain pyroelectric sensors. The energy deposited on the window, is re-radiated as heat, and it is this that is measured
Hello! Is there a way to measure the estimate average power as a DC voltage instead of using the peak power? I'm trying to read average power of a pulsed laser as in your video but I need to make it monitored by a microcontroller ADC.
You could read the pulse from a pyroelectric sensor with a microcontroller. The ADC's even on an arduino are probably fast enough. After that, a bit of math and you have your average.
@@LesLaboratory In my case pulse width is 3ns and period 333ns. I guess ADC sampling of MCU cannot capture that. Dont you think I need RC filter before the ADC? Im interested in average.
@@doncarlos8836 ah, ok, so the big question is, what sensor are you using for this? Pyroelectrics always output a fixed pulse width on the order of microseconds, so not a problem. Photodiodes on the other hand can have picosecond risetimes, so you would need to build an integrator for it. An RC filter may well be good enough.
what is the theory explaining how pure nitrogen increases the output by more than just the amount of non-nitrogen gas in atmosphere?
Nitrogen is the Lasant. Oxygen, will suppress laser action, therefore pure N2 is best. I know I have seen a study in the literature, where the effect was measured, but I don't have the reference to hand just now.
(edit)
oops didnt see it was answerd already