We measure the stress transients resulting from pulsed excimer laser irradiation of polyimide at 351, 308, 248 and 193 nm, using thin (9 μm) piezoelectric PVDF (polyvinylidene fluoride) films. We find that fluences between 3·10-3 and 102 J/cm2 generate peak stresses between 104 and 109 Pa. Further, the results show three ranges of fluence where different physical mechanisms mediate the stress generation. In the lowest range of fluence, subsurface thermal decomposition (for λ = 351 and 308 nm) and photodecomposition (for λ = 248 and 193 nm) govern the generation of the observed stresses. At higher fluences we identify two regimes, independent of laser wavelength, where the gas dynamic expansion of the ablation products and plasma formation and expansion, are responsible for the generated stresses.

The mechanisms responsible for the generation of stresses by pulsed-laser energy deposition in solids are elucidated with special attention given to laser-tissue interactions. These mechanisms include thermal expansion, subsurface cavity formation, ablative recoil and plasma formation and expansion. Scaling laws are presented for the magnitude of the stresses generated by each of these processes. The effect of laser parameters and material properties on the magnitude and temporal behavior of the stress transients is considered. The use of these scaling laws in conjunction with measurement of stress transients induced by pulsed laser sources may be a powerful tool in determining the physical processes which control the response of materials to pulsed energy deposition. In addition, the controlled generation and accurate measurement of acoustic transients may have important diagnostic and therapeutic applications.