Chromium-doped chalcogenide lasers

Broadly tunable near- and mid-infrared lasers are of interest for a variety of applications including high-resolution spectroscopy, metrology, pumping of nonlinear optical frequency converters such as optical parametric oscillators (OPOs) and standoff chemical sensing. Tunable laser sources in the 2-3 um region include Cr2+ doped chalcogenide lasers; cryogenic systems, such as color center lasers; limited tunability devices, such as Tm and Ho lasers, gas or chemical lasers, and diode lasers; and nonlinear optical devices such as OPOs. Transition-metal-doped chalcogenide lasers are of high interest because of their high versatility, broad room-temperature wavelength tunability, high optical efficiencies, and their potential to be scaled to high powers via direct diode or fiber laser pumping. To date, continuous-wave, gain-switched, Q-switched and mode-locked laser operation has been demonstrated. Material advantages include broad absorption and emission bands, high fluorescence quantum efficiencies at room temperature, high gain cross-sections, and minimal loss mechanisms such as excited-state absorption or upconversion. Additionally, the materials can be produced by a variety of methods, including several direct growth techniques and diffusion doping. The principal material disadvantages include a relatively large change in refractive index with temperature (large dn/dT), which can induce thermal lensing, and a short, microseconds, energy storage time. In this paper we review fundamental material properties, the current state-of-the-art of continuous-wave and pulsed Cr2+ doped chalcogenide lasers, and recent research results.