What is the active medium used in Er:YAG lasers?

The active medium used in Er:YAG lasers is a solid-state material, specifically erbium-doped yttrium aluminum garnet (YAG). In solid-state lasers, the laser medium consists of a solid crystal or glass in which the active ions (in this case, erbium) are embedded. When pumped by a suitable external energy source, such as a flash lamp or another laser, the erbium ions become excited and can emit light at specific wavelengths, which in the case of Er:YAG lasers is around 2940 nm, a wavelength highly absorbed by water and hydroxyapatite, making it effective for dental procedures, particularly in hard tissue applications.

The other states of matter such as liquid, gas, and plasma are not utilized as the active medium in Er:YAG lasers. In liquid lasers, solutions of dye or other materials serve as the medium, gas lasers use a gaseous mixture, and plasma lasers involve ionized gases. Each of these types operates on different principles, which are distinct from the mechanisms involved in solid-state lasers like the Er:YAG. The solid-state design allows for greater stability, efficiency, and the potential for miniaturization, making it particularly advantageous in clinical settings.