О Механизме Поглощения И Восстановления Пропускания Излучения В Канале Мелкомасштабной Самофокусировки Короткого Лазерного Импульса В Неодимовом Стекле

Abstract

In the study of small-scale self-focusing (SSF) of a 0.5 ns Nd-laser pulse with 3-5 GW/cm2 intensity in Nd-glass samples, in addition to the characteristic filamentary damage, spectral broadening and laser radiation scattering, a jump in absorption in glasses at the wavelengths 1.06 µm and 0.66 µm was registered also. The coefficient of the induced absorption (IA) in the samples reached 0.15 cm– 1. Restoration of the transmission in the media after the end of the laser pulse had occurred over the time of 15-35ns for phosphate and 5-10 ns for silicate glasses. The physical picture of the IA effect detected as far back as the 1980-s, however, had not been clarified. Current analysis of the experimental data has shown that the absorption jump could be caused by the rapid populating of the 4I11/2 lower laser level of Nd3+ ions in glasses due to the nonlinear processes in the SSF channel: Raman scattering and spectral broadening of the laser radiation. The rates of the 4I11/2 level depopulation and recovery of the transmission were determined by dimensions of the regions with excited Nd3+ ions arising in the glass samples at the interference of laser and scattered radiation as well as by thermal properties of glasses.