Pulsed Lasers and Dust-Off Gas

[Eidetic]

The other night I thought I'd blow a bit of "Dust-Off" "air" through the cavity of my old pulsed ruby laser to help cool in down a little before the next pulse. There's a vent tube to blow nitrogen through for that purpose, but I didn't have the nitrogen handy. It's a small air cooled ruby laser with a helical flash lamp.

I pulsed the laser and the "pop" normally heard was a bit louder than normal. Next pulse, no output! What?!? Tried again watching it this time ... lamp fired but no output.

So I opened it up and the normally clear vent tube was black! Opened the cavity for the very first time and everything is covered with a uniform layer of black "soot". WHAT?!?!? No evidence of arching, nothing burned, nothing broken, ruby intact, reflectors on the rod ends were outside the cavity and therefore still clean.

I cleaned the "soot" away with acetone and methanol as well as I could see, reassembled and now it works again but at 2/3 its original output. Here's my questions:
1) Is it well known by everyone working with pulsed lasers that one NEVER uses canned "air" in pulsed laser cavities?
2) Is the "soot" carbon deposited by the UV from the flash lamp reacting with the gas from the can?
3) Is there a better solvent for carbon than methanol (which worked better than the acetone)?
4) Should I have removed the trigger wire from the flash lamp to clean it better?
5) Am I a freakin' idiot for filling the cavity with an unknown gas before pulsing it?
6) Should I re-clean everything to try and get that 1/3 back?
7) If I don't re-clean, will the mechanism that's eating up that 1/3 output eventually break the lamp or ruby?

Thanks for any comments!

[shrad]

these use a mixture of flammable gaz for propellant (just shake it upside down and press the button, propane-like shower)

this mixture surely contains volatile crap which produced the soot

it was fired by light action alone, or electrical arc under the maybe part-conductive gaz mixture

no luck with that one...

if you want to blow gas through a laser head, use CO² cartridges like those used for cream whippers or paintball guns (cream whipping CO² is food grade so may be better, and don't forget to use a whipper to blow the gaz)

avoid N2O or any other oxidizer if you don't want flammable (or psychedelic) experiences

[300EVIL]

F2HC-CH3 Difluoroethane-1,1 (R152a) + Crazy Output Flashlamp + Pump Cavity = Primed COMBUSTION CHAMBER!

Sorry Bob, I'm going with No. 5 on this one....

Oh well, live and learn, I've done some stupid things before too. As for the output, you may have fried some coatings on the cavity or it's still contaminated with a thin layer of burnt Difluoroethane. I am glad to hear it didn't go off like a bomb!
Adam

[Eidetic]

Yes Adam, I agree. I want to hear it from others to reinforce my lesson.

[dsli_jon]

Hey Robert -

Sorry to hear that... glad you didn't blow yerself up.... or the ruby...

Adam - question - what would you think of recommending to Robert a WEAKened solution of 'HF' (hydroflouric acid) ? We have some down here, and if you think that might be a solution for all parts in the cavity,
Robert, you are welcome to come down and use some - for obvious reasons, I certainly can't 'send it up'...

IF you think HF might be too-risky (fyi, for others: strong-enough HF dissolves both glass and BONE.. ) what about 'MEK'?

Just some thoughts...
j

[Laser Ben]

Well, hopefully you have it back up and running full power by CLEO!

[HD58PHD]

No.5

15 char.

[tocket]

These compressed gas cleaners contain different gases depending on manufacturer and legislations. Here in Sweden I've only seen either products containing either butane or a mixture of dimethyl ether and 1,1,1,2-tetrafluoroethane. Both are combustible, but when tetrafluoroethane burns it will produce hydrogen fluoride as well as other nasty things that may well permanently damage your optics.

So, in response to dsli_jon, I don't think HF solution is something you want on or near your laser. It's one of few the chemicals that will attack glass, so you definitely don't want it near any optics. It also happens to be very toxic and will give you really bad chemical burns. Getting HF solution on as little as 1% of your skin can kill you.

In my experience soot is best removed mechanically. You can only get a small part of the soot to dissolve in a solvent. Some water with a little detergent added may help though.

As for why it happened, you definitely managed to ignite the gas - either with a spark, or with the very intense light. The soot came from incomplete combustion of the gas, because there wasn't enough oxygen in there. Had there been a better oxygen balance it would have burnt more cleanly, but the explosion would have been more violent.

[Vidal Wolf]

wow, your lucky the lamp didnt shatter taking the rod with it in the process!
losing 1/3rd isnt too bad considering you could have lost 3/3rds.
Hope ya find the missing third!

[dsli_jon]

Hey tocket -

Getting HF solution on as little as 1% of your skin can kill you.

Not a 'defensive' comment, but just fyi, the solution we have is pretty-weak - like ~1% IIRC - basically, an 'oxide remover' - I don't think this stuff we have would be that 'deadly', unless you, like, bathed in-it... and of course, proper-precautions would be taken, in-use... I only thought of it cause it cleans glass / metals of any 'funk' *really* well... But you make a good-point... (even vs thinking of suggesting 'MEK'...) :

In my experience soot is best removed mechanically. You can only get a small part of the soot to dissolve in a solvent. Some water with a little detergent added may help though.

Some 'mild dish-soap' and water might, in-fact, work well, Robert - I've also seen it work wonders, where even acetone does not work as-well (ie: 'CDAR' ar-coated windows...)

PS - off-topic - in-case I have never told you, THANKS for 'Chroma' -

cheers..
j