Mechanisms of Ionization of F-2-Centers in Laser Media on the Basis of Lif Crystals

F2 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 F2-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 F2-centers to laser radiation (the “hard” excitation regime) is explained by the dissociation of (F 2 + , F–) pairs induced by two-step ionization of F2-centers: (2hν > 4.5 eV) → F2 → (F2)* → F 2 + + e; F + e → F–; F 2 + + F– → 3F.