Passive Q-modulation of optical cavities by KCl crystals containing OH(-) -ions

The investigation of color centers in KCl-OH crystals additively colored in potassium vapors is described. It is found that irradiation of colored crystals by white light results in the formation of a series of F aggregate color centers which are stable at room temperature. The use of such crystals as passive laser shutters to Q modulate the cavity of a YAG-Nd(3+) laser (1.064 micro m) is described. It is found that working color centers that are thermally and optically stable at room temperature can be obtained by additive coloration of hydroxyl-doped KCl crystals in alkali metal vapors followed by exposure to light. Similar centers are unstable at room temperature if the KCl crystals contain no OH(-) ions, and cannot be used as passive shutters. An interpretation is given of the mechanism underlying the stabilization of working centers.