An efficiency study of transient wave generation in a thermoelastic layer with a pulsed laser

The efficiency of transient wave generation in a thermoelastic silicon laye r excited by a pulsed laser is considered. First a principle-based transfer matrix formulation with relaxation effect, also referred to as the general ized dynamic theory of linear thermoelasticity, is used in obtaining transf er functions between the input heat field and the elements of the thermoela stic state vector. The second sound effect, through this relaxation time te rm, is included to eliminate the thermal wave travelling with infinite velo city as predicted by the diffusion heat transfer model. By employing the fa st Fourier transform (FFT) algorithm, the transient response of a silicon t hermoelastic layer under a thermal excitation (by a pulsed laser) is invest igated to quantify the conversion efficiency from thermal to mechanical ene rgy. The transient acceleration, stress, heat, temperature, and mechanical power flux responses are presented. The pulse duration of the laser excitat ion is submicrosecond level and, consequently, a large number of modes of m otion are excited. Rigid body singularities are eliminated by considering t he higher order time derivatives of the state variables. A layer made of bu lk silicon under this laser excitation is considered and it is found that t he amplitude ratio of the applied heat field to the propagating heat flux a t the data points is in the order of 10 degrees. The ratio of the applied p ower (heat flux) to the generated mechanical power flux is in the order of 10 degrees. The resulting rigid body motion of the layer due to the laser e xcitation is excluded in calculating the mechanical power.