Ultrashort pulse induced elastodynamics in polycrystalline materials. Part II: Thermal–mechanical response

Abstract

Near-field thermal–mechanical responses in polycrystalline gold films considering grain size effects and temperature-dependent thermophysical properties are examined using the generalized thermo-elastodynamic model formulated in Part I. Ultrashort laser-induced transverse and radial thermal stress waves are attenuative, broad in bandwidth, and dispersive with extremely high frequencies. Grain size effects on thermal response are found to be so prominent that the stress fields induced in the polycrystalline film considered for the study are consistently more intense with decreasing averaged grain diameter. The normal and shear stress fields induced by a below melting threshold fluence are low in amplitude but extremely high in frequency response and power density. With the former not exceeding 20 MPa and the latter of the order of 1018-to-1019 [W/m3] in magnitude, non-melting ultrafast heating that generates no plastic deformation is profound with the potential for initiating fatigue micro-cracking in near-field and for inflicting physical damage.