Answer:
The ruby laser was the first to be used in medicine in the 1960’s to repair detached retinas. It emits a wavelength of 694 nm. The Q-switched ruby laser permits a tremendous pocket of energy in a short burst which is absorbed by blue and black amateur tattoos, sparing the epidermis. Multiple treatments are required, and the laser is very expensive. For tattoo removal, additional lasers are the alexandrite (755nm) for green tattoos, and the Q-switched ND:YAG laser (1064nm) for black tattoos.
Excimer lasers use halide gases that are stable only in their excited state. Four halides may be used (XeF, XeCl, KrF, ArF) emitting light between 351 nm and 193 nm. Penetration into tissues is extremely shallow. Well accepted in ophthalmology but not yet clinically feasible in plastic surgery. The halide gases are extremely toxic and can be dangerous if not contained.