TIME-RESOLVED SPECTROSCOPY FOR RADIATION-DAMAGE PROCESSES INDUCED BY ELECTRONIC EXCITATION IN INSULATORS

We review current studies by means of femtosecond time resolved spectr oscopy on defect formation induced by valence-electron excitation in h alide crystals. We first summarize the characteristics of several tran sient relaxed configurations of electron-hole pairs or excitons which play important roles in the defect formation process. Then, the result s on the self-trapping process of holes in this material are described to show the specific feature revealed by the femtosecond spectroscopy . Finally, the dynamics of the Frenkel pair formation in alkali halide crystals is discussed based on the results obtained for several cryst als at wide temperature range from 5 to 300 K. Emphasis is placed on t he new feature of damage mechanism which rakes place during the lattic e relaxation of the localized electron-hole pairs.