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ArcticMyst Security by Avery

A Gas Laser Primer For the Noob

Roam

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Also it should be pointed out that when u have external mirrors like some older HeNes, all the modes have the same polarization... so if you put a polarizer in the beam, rotate the transmission axis of the polarizer and look at the spectrum of the laser light as a function of polarization u can extinguish or bring up all of the lines by changing the axis of the polarizer. So there is enough gain for several frequencies to oscillate.

Whereas HeNe's with internal mirrors, u can actually get rid of some lines and keep the others by putting the polarizer outside the tube because they have different polarization.
 





diachi

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Argon Ions - oh how I have learnt so much about those.

Lets see now.

First of all if your going to get an argon ion laser, you'll usually come across two different types - single line and multiline. Single line argons emit one wavelength, and multiline several. You can test if your laser is multiline or singleline (ML/SL from here on in) by shining it through a diffraction grating, diffraction mirror, a prism, or in a pinch at a compact disc. Multiline lasers will reflect their multiple wavelengths as a row of dots. I still haven't caught up on the numbers for the nm's they emit. 488nm however is the most common SL and most dominant argon line.

When your out shopping for an argon, theres two things you HAVE to check with regards to the power supply.

1. Can I power it?
2. Is it in the same range as my outlets?
3. Do I need a spare space heater in the house...

For #1, don't grab that cheap monster 5 watter if its 3 phase, if you don't have the utility to power it.

For #2, check to see the lasers power supply will run of your line voltage - its no good getting the laser home and finding the psu is a 220v model and your line voltage is 110 - the other way around can be sorted with a beefy step-down transformer (don't worry, I've done it!)

The most common lasers you'll find in surplus argons are the JDS uniphase units, and the ALC 60X. NEC's are popping up often enough too. On rare occasions, so do ILT's (including their whitelight models *drool*)

Small argons that the hobbyist is likely to come across need forced air cooling. Lots of it. Thats why theres at least one honking big fan in just about every small ion laser pic - they generate a tremendous amount of waste heat, and the tubes will melt down quickly without it (assuming the thermal protection isn't working LOL). I used to use mine to heat my room in winter before I sold it! A good ML tube can do over 150mw, and up into the low 100's for a SL unit. They have a heated cathode, and the tubes can take up to a minute or two to click into life - they're not like HeNe's that wink on as soon as you hook up power (provided the HeNe has no CDRH saftey delay).

During this warmup time the filament is coming up to temperature and; in a linear design supply, the filter capacitors are precharging to ~100 volts; for larger lasers this can be up to 300 volts. Both large and small frame ion laser power supplies will kill you if you tinker around inside them. Capacitors can dump thousands of amps in a short period, and blow off digits if you survive. Best leave the lid on the supply ;)

Lasers like these like to be run once a month for 20 minutes to an hour to keep them happy otherwise argon gas migrates into the tube walls, the pressure goes up and they become hard to start. Called a maintenance burn, its a monthly procedure that most argon owners remember to carry out - hence we often post reminders in the gas forum to fire up those argons.

A burn is a justifiable term as the plasma in the tube burns hotter than the sun hence the need for the 150+cfm fans on some models. If your REALLY lucky you'll come across an Ar/Kr (argon/krypton) unit that is called a white light laser. Different mixes of the two gases give different ratios - some tend to favour the red/yellow krypton line over the blue/green argon lines.

If you end up with a JDS Uniphase Argon or an ALC 60X, the remote controllers are easy to build. You can then use this to vary the tube current up from idle around 4A to 8.5A (thats the safe range) or boost it to 10.5A if you dare, but this shortens tube life dramatically so keep those 10.5A burns short.

*phew*
buffer empty completed ;)


One thing to point out is that the 488nm line on Ar ion lasers isn't always the strongest. The gain of the 514nm line increases as the tube current increases - so on medium-large frame ions ( Possible on small, air cooled too - My memory is a little rust on the subject ) the 514nm line can be stronger. You'll notice it when you turn the current up from idle and the beam changes from blue-ish green to more of a green-ish blue. :)
 

LSRFAQ

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Unless you drive it from ultrashort pulses from a transmission line and thyratron, HeHG has the single pass gain of a sun dried tomato. I spent months pulling every paper on it.
The home made HeHg rarely breaks 15 mW total, using the Scientific American design. One fellow in Italy built one recently.

The Russians spent millions of Rubles on it during the days of the USSR, I doubt they missed anything, although they had some spectacular uses for it. The gain saturates easily for some reason that always baffled them.

Far better to use oxygen, argon, or xenon for a home made pulsed laser. Especially Oxygen or Xenon.

Steve
 
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Interesting, I haven't done much reading on it as there's no way for me to do it in a few years anyway. Not really the project for a dorm scenario ;)
 

LSRFAQ

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Find a copy of Gas Lasers by Bloom. Then find Gas laser Technology by Sinclair and Bell, the later has plans for a very high power HeHg. The plans require a thyratron for high power at a high rep rate, and use techniques that should really be done by a pro glassblower. Then borrow a copy of CRC Handbook of Lasers II, Gas Lasers, edited by Webber. I have the latter, and at 170$ used, they do not go cheap. I can't say go out and buy a copy of Webber, its nice, but gives little practical detail. Most of what is in Webber is keyword findable on Google these days.

Note to others, unless you already know your way around glass-working and high vacuum, the above books are of not much use to you, unless you have passed at least Algebra Two and College Physics II, Electromagnetics. Bloompyle has that special interest and prior knowledge, and he will find them useful.


Sinclair's book covers actual construction, and Webber's book is a massive list of gas laser lines with annotations and references, sorted by wavelength and element. Webber covers deep UV to Far IR. If you need a element looked up, on the rare times I'm actually home, I can look in Webber.

Bloom, Bell, and Sinclair are founders of Spectra Physics.

Steve
 
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First two are added to my cart (had to find Gas Laser Technology outside of Amazon). Amazon also has the CRC Handbook for $90 used. Next time I order anything from Sam, I'll see if I can't borrow it to see if I find it worth $90.

I've been reading a lot of The Laser Guidebook (second edition) by Hecht, Lasers, Ray Guns, and Light Cannons by McComb, and Intro to Laser Physics by Shimoda.

The first two are pretty decent, I have another but it measures light in um and mm rather than nm, which gets old quick. I also have no idea was an angstrom is.

The physics book is about as hairy as the 90's, but I can force myself to read it, I just don't understand much of the math, but I get the concepts. Once I can start my schooling I'm sure it'll all freshen itself back up again. Really starting to hate the little attention I paid to math in grade school.

I think the most expensive part will be the gas filling, I believe Sam can blow the glass, but I also didn't ask for a cost so who knows there.

Once I get it built, not lasing, built, the psu will be the second challenge. Pulsed HV is not a game.

Anyway, thank you very much for those book titles. I'm sure I'll be able to put them to good use :) I mostly read up on HeNes, as they're my ultimate interest in gas at the moment. Do these books have decent information on them as well? Or is it mostly the gas that's outside of our reach? Also, what would you say the jargon level is in these? I have a book here that goes into heavy detail on points of information that really mean nothing in the grand scheme of things. Almost to the point where I wonder if it was only added to lengthen the book. Will these follow a similar pattern?

Do you have another way that I could reach you more readily? I'm always on the lookout for an individual that I can talk to about gas, and learn something from. More than just reading static text from the FAQ, or a book. Don't get me wrong, I love reading both, there's just something to be said about a good conversation.
 




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