Miniature active elements for color-center lasers with an extremely low lasing threshold

An active medium was formed from lithium fluoride single crystals with the maximum concentration of the active centers (F₂, F₃⁺), reaching the range of concentration quenching. The coloration method made it possible to reduce greatly the concentration of parasitic aggregate centers and, consequently, the optical losses in the medium. The lasing threshold for the F₂ and F₃⁺ centers was 4 and 60 kW/cm², respectively.