Holographic inferometry of isotherms during laser drilling of fused quartz

The propagation of heat into fused quartz during drilling with CO2 laser radiation had been studied using differential holographic interferometry. This technique yields the temporal evolution of the thermally induced optical path difference in a cross section through the sample in a plane which contains the longitudinal axis of the drill hole. With the assumption of cylindrical symmetry, a portion of the temperature field in the sample has been obtained from these optical path length differences and is compared to the results of theoretical models for heat transfer from a high-aspect-ratio laser-heated drill hole. Isotherms derived in this way have been obtained during CO2 laser drilling of fused quartz in normal gravity and under the reduced gravity conditions of the NASA KC 135 aircraft under parabolic flight conditions. Heat transfer from a pre-drilled hole absorbing laser radiation has also been studied to evaluate the possible effect of material removal on heat transfer. Comparisons of these thermal profiles with those generated by numerical modelling of heat transfer from a laser-heated drill differences. Possible sources of these differences measured isotherms are discussed.