Formation, optical properties, and laser operation of F−2 centers in LiF

Abstract

Formation conditions, optical properties, and lasing behavior of F−2 color centers in LiF crystals are investigated. The optical pumping cycle of the three-electron defect is found to involve intermediate transitions of small efficiency into some metastable energy levels (having a lifetime of several seconds). This process could either be intrinsic to the F−2 defects (e.g., intersystem crossing into quartet states) or it could be caused by (low efficiency) optical ionization of F−2 centers and electron capture in unstable traps. While cw laser oscillation is prevented by a resulting bottleneck, efficient tunable pulsed laser operation in the 1.1–1.2-μm range is possible at room temperature.