A Gas Laser Primer For the Noob

[scumbagatheist]

Boy, did this get esoteric...

 

[Sigurthr]

Heh I think that may be my fault, sorry.

Gas lasers generally fall into two main categories: neutral atom and ion.

An example of a neutral atom has laser would be your venerable HeNe. They require low power input and are relatively efficient. Simply pass enough current to get a stable arc at a high enough voltage to cause dielectric breakdown, slap on some mirrors and you're golden. These are essentially cold cathode tubes.

Ion lasers require that the gas be ionized prior to lasing, so there is a huge energy input required to get anything out, and since you need to put so much energy in you have to remove so much as waste heat. It is not uncommon to put in 100Watts of power to get 1mW of output on high efficiency ion lasers. The other. 99.999Watts have to be removed as heat. Typically the bores are made of ultra high temp ceramics like BeO (super toxic if inhaled) in order to withstand the stresses. The intense electron flow in the bore causes sputtering and ablation of any metal parts as well as trapping of gas within the bore walls. Due to pressure rises from temperature levels needed for ionization the ignition voltage needs to be significant. Iirc there was some research done in ionizing radiation induced ion lasers but the levels of radiation flux needed made the unit not feasible. Radionuclides are commonly used to aid ionization within vacuum tubes but the levels of ionization needed in ion lasers are extreme to say the least.

That clear things up any?

 

[scumbagatheist]

That is a great start, thanks. Some basic theory goes a long way. I can tell that I am going to have to bust out with my periodic table!

So, if I understand you correctly, then you need as much as or more than 800W to fire up your multiline 80mW Uniphase?

What does uniphase mean?

 

[IsaacT]

Uniphase is a brand

 

[LtKernelPanic]

So, if I understand you correctly, then you need as much as or more than 800W to fire up your multiline 80mW Uniphase?

Argons are power hungry beasts unlike HeNe lasers which are fairly effecient compared to other gas lasers. I could be remembering wrong but IIRC when my 100mw multiline argon (also a JDSU Uniphase) starts the PSU briefly ramps to full power to get it lasing it would be pulling at least 1200W (120V@ 10A) from the wall. I haven't measured it in awhile but again IIRC running at full power (which I don't do very often) my Kill-A-Watt showed it was drawing 13A (1560W) for both the PSU and laser head.

 

[IsaacT]

For a large Argon Laser, it could require up to 27000W to maintain lasing conditions. (according to some quick searching as to what Voltage and Current requirements large Argon Lasers have, plus some google mathing ).

 

[Sigurthr]

At idle my argon draws about 500W and puts out 6 lines for a total of 5mW output. For rated 40mW operation the tube needs 7A anode current and draws 1097Watts of power and produces eight lines. For the maximum of 80mW the laser needs 9.5A anode current and iirc draws close to 1.35kW of power. The cooling fan I think eats another 200W of power as well. The 100W/mW figure is just a best case scenario rule of thumb that doesn't take in filament power into consideration.

 

[bloompyle]

Lots of good information here, but I did not see this going past HeNe so fast O.O

 

[scumbagatheist]

I certainly hope it does. I want to learn more about ML systems, optics/mirror basics, etc...
I really appreciate all the great info so far.

 

[bloompyle]

ML systems with HeNes are pretty much hit or miss. It isn't guaranteed, even if it's already outputting. If the mirror on mine moves even just a micrometer, it goes to just SL 612nm. It's luck really. You can make an ML using a 1B tube and some HR mirrors, though nothing is guaranteed even via this route. There is no rule that using mirrors will get you what you want, depends on the mirror, tube strength, and how long it's been since your last leprechaun visit...

 

[Sigurthr]

I'll just leave this here...

Needless to say the plans are literally on the table...

The only thing holding me back is sourcing some angle. I received a tip that there might be some in the local hardware shop left over from a special order. I'm going to take a trip over soon to find out.

 

[vk2fro]

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

 

[bloompyle]

There's a third, less common, argon type. You'll see more on that next week if I'm lucky with the postage

 

[n2stuff]

There's a third, less common, argon type. You'll see more on that next week if I'm lucky with the postage

That's cruel to make us wait bloom. Give aleast a hint. You know us gas freaks cant wait a week:crackup:

 

[bloompyle]

Patience is a virtue, goodnight gentlemen

 

[Sigurthr]

I'm guessing an intracavity prism/mirror tunable ArION.