HYPERBOLIC HEAT-CONDUCTION EFFECTS CAUSED BY TEMPORALLY MODULATED LASER-PULSES

In non-destructive testing (NDT), the intensity of laser pulses may be temporally modulated to improve the signal-to-noise ratio of ultrason ic signals. The purpose of this work is to determine the time scale on which hyperbolic heat conduction effects are significant in ultrasoni c displacements and stresses for temporally modulated laser pulses, un der the assumption that the heat wave speed equals the longitudinal wa ve speed. A one-dimensional model with a finite train of heat flux pul ses is investigated. Using the Green and Lindsay model, it is found th at the critical modulation frequency in steel, above which hyperbolic heat conduction effects will become significant, is 2.26 GHz. A dimens ionless factor is given to calculate critical modulation frequencies i n other isotropic materials. The signal enhancement potential of tempo ral intensity modulation is apparent in the numerical results.