Self-optical breakdown and multipulse optical breakdown of transparent insulators in the femto-nanosecond region of laser pulse widths

摘要

This review is devoted to an investigation of the nature of the optical breakdown of silicate glasses. Experiments have been carried out in a wide range of wavelengths, laser-radiation pulse widths, and focusing spot sizes. It is shown that the threshold power density for optical self-breakdown of borosilicate glass at a wavelength of about 1 μm is independent of the radiation pulse width in the range from 2 * 10~(-13) to 3 * 10~(-8) sec. This result cannot be explained in terms of existing theories. It indicates that the breakdown mechanism is associated with collective ionization of the insulator as a whole and not with the accumulation of electrons as a result of their individual ionization because of multiphoton, tunneling, or avalanche excitation. Special attention is paid to investigating electronic excitation processes in alkali- and lead-silicate glasses.