GLASS LASER DAMAGE RESEARCH

The report covers an experimental investigation into the damage of glass by high intensity, 1.06 micron wavelength light pulses of millisecond duration. Damage due to optical absorption by impurities is demonstrated by ease of damage, above some intrinsic level, proportional to the measured optical absorption. An additional source of damage is optical absorption at 1.06 micron from the excited (fluorescing) state of the neodymium ion. Evidence for this mechanism is presented, and an approximate value of the excited state absorption cross section determined. The nonradiative decay (heating) back to the initial excited state is assumed to be the source of damage, and this appears reasonable from other data. Studies of opto-acoustic coupling are presented and their connection with stimulated Brillouin scattering denoted. Measured coupling constants for different glasses, which are shown to be devoid of impurity optical absorption effects are presented. Stimulated Brillouin scattering as a cause of damage suggests correlation between these opto acoustic coupling constants and damage thresholds. Initial qualitative agreement between the two is encouraging enough to warrant further investigation of this technique as a way of predicting damage thresholds. See also AD623309.