Damn,
I got to make one of those with a 8 foot light tube and my desiccated breath. I read how to do it long time ago. Easy as: HV circuitry, Vacuum Technology, Glassworking, electronic impedance matching, optical alinement, material procurement and week of good luck and money to burn.!
That laser is money well spent man, bravo!
I read if your beam goes through a 1/2 wave plate or something, it's stops the destructive feedback to the OC. As is (your setup)the beam bounces back with circular polarization.
Want deeper penetration!!! ;D ;D ;D