COLOR CENTER LASERS

Color centers in alkali halide crystals can be applied as high-gain active materials in tunable solid state lasers. When cryogenically cooled and optically pumped, these laser crystals have low threshold pump powers, relatively high output powers, and are smoothly tunable over a large fraction of their broad emission bands. Using various color center types and host lattices, the combined tuning range of color center lasers covers presently the near-infrared region from about 0.8 to 4-mu-m. In single-mode cw operation color center lasers have extremely narrow spectral line-widths; in mode-locked operation they can provide pulses with ultranarrow temporal widths. These properties make them very attractive for spectroscopic studies requiring high spectral or temporal resolution. This paper reviews the optical properties of the main laser-active color center types, the techniques used for their production, and their laser characteristics. Furthermore, a brief summary is given on the application of color center lasers.