Mechanisms of Ionization of F_2-Centers in Laser Media on the Basis of LiF Crystals

摘要

F_2 color centers with a superhigh concentration (5000-cm~(-1) absorption coefficient at 450 nm) were formed by high-density electron beams in a layer of LiF crystals of micrometer thickness. The F_2-centers excited by high-power nanosecond wide-band optical pulses (the "soft" pumping regime) efficiently amplified the laser radiation and showed high stability under these conditions. A low stability of F_2-centers to laser radiation (the "hard" excitation regime) is explained by the dissociation of (F_2~+, F~-) pairs induced by two-step ionization of F_2-centers: (2hv > 4.5 eV) → F_2 → (F_2)~* → F_2~+ + e; F + e → F~-; F_2~+ + F~- → 3F.