Crystalline Mid-Infrared Lasers

A survey of the well-established as well as newly emerging ion-doped crystalline lasers, operating in the mid-IR spectral range between 2 and 5 µm, is presented. The review includes rare-earth- and transition-metal-based ionic crystals, as well as color-center lasers. The emphasis is made on state-of-the-art compact all-solid-state room-temperature tunable sources, belonging to the broad class of vibronic lasers. The announcement of the efficient high-power room-temperature operation and super-broad tunability, as well as the possibility of generating ultrashort pulses from the novel class of chromium doped chalcogenide lasers led to a strong revival of research interest in vibronic laser systems, involving 3d n transition-metal ions. The review outlines the underlying physics of mid-IR lasers and sorts out the essential spectroscopic and laser characteristics, allowing assessment of the suitability of laser materials to serve as active media in diode-pumped laser systems.