CW or pulsed lasers in which the active medium is a solid matrix (crystal or glass) doped with an ion (e.g. Nd³⁺, Cr³⁺, Er³⁺). The emitted wavelength depends on the active ion, the selected optical transition, and the matrix. Some of these lasers are tunable within a very broad range (e.g. from 700 to 1000 nm for Ti³⁺ doped sapphire). Pulsed lasers may be free-running, Q-switched, or mode-locked. Some CW lasers may be mode-locked.