Tunable cw laser operation in the 1.45–2.16 μm range based on F+2-like centers in O−2 doped NaCl, KCl, and KBr crystals

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Abstract
In additively colored NaCl, KCl, and KBr crystals doped with O−2 anionic molecular impurities, a laser active defect is formed by optically induced association of F centers with oxygen‐vacancy defect pairs. The formed defect has F+2 ‐like properties in terms of optical transition energies, Stokes shift, and optical gain. It can be regarded as an F+2 center attached in different possible configurations to a neighboring double negatively charged oxygen anion impurity which replaces a halide ion. Stable cw laser operation could be realized, so far, in the hosts NaCl, KCl, and KBr. Pumped with 10 W at 1.064 μm the NaCl center laser was tunable from 1.45 to 1.74 μm with 1.3 W peak output power at 1.60 μm. The KCl and KBr systems, both pumped at 1.32/1.34 μm, were tunable from 1.66 to 1.97 μm with 170 mW peak output, and from 1.86 to 2.16 μm with 30‐mW peak output, respectively. Depending on the host material the laser crystals do or do not require auxiliary light exposure exciting the higher‐energy transitions of the laser active center in the F center absorption range. The auxiliary F light produces and maintains, by induced F+2 center reorientation, the laser active defect configuration in NaCl and KBr, while in KCl it separates the F+2 center from the O−− impurity.