Ruby laser‐induced frequency dependent refractive index change in KCl:Li⁺ F_A crystal

Abstract

Recently it was shown that FA centres in electrolytically coloured KCl: Li' crystals can be reoriented at room temperature using a ruby laser for pumping [lo, 111. The ruby laser-induced linear dichroism of FA centres was observed to survive long enough that KC1: Li' crystals could act as a temporary memory [12]. During the durability investigation of the memory ruby light pulses were incident on the crystal every 25 s and the duration of a single pulse was 50 ns and the approximate energy was 30 mJ. It was found that several days duration of the memory could be realized when the crystal was kept in dark during the continuous ruby light pumping.In order to optimize the operation of the memory it was found that an additively coloured KC1 : Li' crystal provides a longer durability than an electrolytically coloured one [13]. Furthermore in that study it was proposed that the ruby light-induced temporary change in refractive index could be in principle applied for the purpose of photonic switching. Actually when a ruby laser pulse is incident upon the KC1:Li' crystal there exists simultaneously switching in the optical density and refractive index of the crystal because of the light-induced reorientation of the FA centres. The reorientation is not permanent at room temperature and as a result of thermal reorientation the centres tend to attain random orientation.In this note we study the frequency dependent refractive index change of FA centres, which is caused by ruby laser pumping at room temperature. So far such a study has not been reported in the literature. Our object was to inspect especially the strongest change of refractive index, which can be found for some specific probe wavelength during the ruby light pumping.The Li+-doped KC1 crystals were grown using the Czochralski method. The crystals contained 1 mol% of LiCl in the melt and the additive coloration was performed using the I)