This is exactly what we are talking about in the other thread. Most lasers have the ability to be turned on and off with a 5V TTL level signal similar to what you would use to give step and direction to a motor driver. The time it takes for the laser to come up to full power, or say 90% of full power is the rise time, and it varies for different types of laser excitation and even for different manufacturers of similar lasers. Most RF excited lasers keep the gas in an energized state just below the threshhold that would cause them to lase. They either do this by requiring the user to keep a constant "tickle" pulse (usually like 1usec at 10khz or so) or they have it built in. I have no idea what the DC excited glass tube lasers use or even if they can keep the plasma in this pre-excited state.
Well that shed some light to it, but as you say, how do they do it a with CO2 laser?
I am asking because my brother is building a CO2 laser (DC excited) and the thought is to build a cnc table for it. But the one thing we can't figure out is how to turn on and off the beam and still have the laser running.