Effect of beam intensity on target response to high−intensity pulsed CO2 laser radiation

Abstract

The mechanical response of various classes of opaque materials exposed in air to high−intensity pulsed 10.6−μm−wavelength laser radiation is described. At beam intensities below approximately 107 W/cm2 (pulse durations of 4×10−3 and 3×10−4 sec), the magnitude of the total impulse delivered to the target is found to depend on the nature of the target material. At intensities greater than approximately 108 W/cm2 (pulse duration of 2×10−5 sec), there is negligible difference in the impulse response of different materials. Moreover, at the higher power densities total impulse delivered to a target by a 0.04−cm2 laser beam is found to be proportional to the physical area of the target up to approximately 8 cm2. These results are correlated with the the interrelationships among the instantaneous laser intensity, the instantaneous pressure generated at the target surface, and the observed state of development of the laser plume. Also reported is a survey of the thermal response of aluminum targets to laser irradiation over this range of power densities. These studies reveal that the apparent thermal coupling coefficient of aluminum remains at the cw value of approximately 3% at incident power densities as great as 105 W/cm2. Between 105 and 107 W/cm2, the optical coupling coefficient goes through a maximum of approximately 6%, then drops to a level close to zero at power densities greater than 108 W/cm2.