Generalized thermo-elastodynamics for semiconductor material subject to ultrafast laser heating. Part II: Near-field response and damage evaluation

Thermal waves and near-field responses including the axial and radial displacements and stresses are investigated in a time window as wide as 10 ns using the generalized thermo-elastodynamic model of axisymmetric geometry presented in Part I. Ultrashort laser-induced thermal waves are found to be fast-attenuating; while transverse thermal stress waves are dispersive and characteristically of broadband and extremely high frequency. In addition, near-field responses and wave dispersion described by the presented model formulation are characteristically different from those modeled using parabolic transport equations for the same laser input parameters. The methodology of accumulated damage evaluation (Oh et al., 2008 [11]) making use of high cycle fatigue and time–frequency analysis is utilized to conclude that thermal stress waves induced by 500 fs ultrafast laser pulses of 0.775 μm in wavelength, 0.005 J/cm2 in fluence and 10 μm in spot size are insufficient to initiate fatigue cracking in the silicon thin section considered in the study.