Theoretical calculations of the consequences of the thermoelastic mechanism for production of stress in solids by pulsed energy input have been performed, and the effect of variations in the acoustic impedance of a transparent backup material and variations in the pulse duration as compared to the acoustic transit time across the penetration depth of the incident energy have been investigated. Experimental verification of the theoretical calculations has been done using a Q-switched ruby laser as an energy source with samples of absorbing glass as targets. It is found that the experimental results give good agreement in the shapes of the stress pulses produced, and fair agreement in the absolute amplitude of the stress, with no adjustable parameters being required. The calculations and experiments demonstrate the validity of the thermoelastic stress-production mechanism in solids when no phase transformation occurs.

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Absorption of intense light, of photon energy greater than the bandgap, produces changes in the optical properties of semiconductors. The induced absorption produced by 1.06-1' laser light in high-resistivity single-crystal silicon wafers was measured, by use of a monitor flash lamp, at monitor wavelengths Am = 1.2 to 2.71'. The Q-spoiled glass: Nd3+ laser produced pulses of typically 25-nsec duration. The induced absorption increased with monitor wavelength, as expected for a free carrier mechanism. As a function of laserpulse-energy density, the transmission immediately following the laser pulse was of the form T(A) = exp( -uxE ) , with ux = 1.7XlO-17 cm' at Am=2.6}L for Si at room temperature. The exponential dependence is in agreement with an analysis of the induced absorption process, and the value of ux is in approximate accord with that calculated from measurements of infrared absorption in doped silicon.

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A circular, magnesium fluoride ring was irradiated with a Q-switched, neodymium-doped glass laser. The sudden absorption of laser energy by the ring produced an internal temperature distribution which could be closely approximated by a cosine function over half the circumference of the ring. The ensuing membrane strains were measured with semiconductor strain gages. Measured strain-time histories were found to be in close agreement with theoretical predictions.