Re: Is it possible to use a nitrogen laser to initiate discharge in a CO2 laser

Your question is a relatively complex one, and I'll try to break it into 
parts.

Starting with your last question first -- the penetration length of 337 nm 
light in N2 at atmospheric pressure -- my response is that you should take 
a quick look on the Web in in your very good Stanford library to get the 
absorption spectrum of ALL the gases in the laser.  I'm happy to comment 
on the physics issues but a grad student like you should do a bit of the 
ground work before asking for help.

Most CO2 lasers will have N2, He, CO2, and (often) Xe.  As you probably 
are aware, most of the gas is He.  My guess is that you'll find that you 
can produce modest ionization with 337 nm output that might be OK to 
provide preionization of the discharge, but that you won't have much luck 
using the N2 laser pulse to provide both preionization and triggering of 
the main discharge.  Preionization effects are generally regarded as 
relatively gentle volume ionization of the region in which you want the 
glow discharge to form and excite the laser medium.  Ideally, 
preionization is done just before or as the high voltage is switched 
across the laser electrodes, so that the residual electrons and induce a 
uniform avalanche.  If you try to apply the high voltage to the electrodes 
well before the preionization and then whack the inter-electrode gases 
with a high enough energy pulse to initiate the breakdown, you'll probably 
end up (in a TEA laser, which it sounds like you're building) with a big 
arc that'll dig a trench in one or both electrodes that will cause similar 
arcs in the future.  These arc's steal energy from the desired glow 
discharge and usually cause the laser to stop operating.  While UV 
preionization is an established technique, I think that use of an external 
laser is probably a pretty tough way to get the job done -- the external 
laser will have the problems noted above, and will be a pain to set up and 
run reliably.

UV preionization has been successfully used in the past using incoherent 
discharges close to the main discharge area between electrodes.  
Generally, corona points or wires are used.  Placed within the electrode 
structures or immediately adjacent to them, these preionizers can either 
be fired independently (using a small modulator or pulsed driver to put 
very high dV/dt on them in advance of the main discharge) or can be 
connected to the main electrodes/modulator in such a way that they ring up 
rapidly in voltage and produce the desired preionization as they initiate 
a small, non-self-sustained discharge that illuminates the main discharge 
region in a bath of low level UV.  There are tons of references in the 
literature as to how folks to this, and it's been long enough since I've 
done it to recommend one technique over another.

Hope this helps!