UV-Induced Color Centers and Gain Measurements in Ce sup 3+ :YLiF sub 4

摘要

The origin of the laser performance limitation characteristis of Ce sup 3+ :YLF have been identified and studied. To understand how stable and transient absorption centers are produced, several experiments were done including temperature dependence of transient decay times, spectral characteristics, growth kinetics, thermal or optical bleaching of these centers, and pump energy dependence. It is shown that the production of these centers results from a resonant two-photon absorption process or excited-state absorption which ionizes trivalent cerium ions. Once in the conduction band, the electrons from the cerium ions can be trapped temporarily at other trivalent cerium sites or permanently pre-existing fluoride vacancies, resulting in transient or stable color centers respectively. In order to clarify the effects of these color centers on the laser gain, single pass gain measurements were done as a function of laser pump repetition rates for several different temperatures. The possibility to improve the Ce sup 3+ :YLF laser with thermal and optical bleaching of these absorption centers is discussed. The energy levels and structure of Ce sup 3+ :YLF is discussed with the absorption and fluorescence spectra, and the possibility of the thermal lensing effect is discussed. Experimental techniques used to characterize the process responsible for the transient absorption are presented. The stable absorption bands, which are observed along with the transient absorptions, are discussed, and their polarization dependence, growing, and bleaching are presented. The single pass gain measurements are presented to explain several lasing problems found in Ce sup 3+ :YLF, and possible gain improvement is discussed. (ERA citation 13:018878)