No, metal backed mirrors but you will need to cool them. On the 4.4kw CO2 I used to work on all of the mirrors were water cooled. They fit in a mount that routed water over the back of the mirror. With q-switched lasers the average power is much lower so mirrors dont need to be as heavy, though I have vaporized the coating off a aluminumizined front surface mirror at 6w average power at 355nm unfocused. Even at work on the machines we make the mirrors do not have an unlimited life, they do "wear" and need to be replaced eventually.