Influence of laser beam profiles on the frequency bandwidth of laser-generated surface acoustic waves

The frequency characteristics of laser-generated surface acoustic waves (SAWs) were investigated depending on laser beam profiles. The laser-generated SAWs were analytically and experimentally compared when using the single-line laser beams of Gaussian and square-like energy profiles. Also, the line-arrayed laser beam in the square-like energy distribution was introduced to generate the SAW that had a narrow frequency bandwidth. The results from both the experiments and the simulations showed the similar distinction of the frequency characteristics in between using Gaussian and square-like laser energy profiles. The SAW by the Gaussian laser beam showed only single peak in the frequency spectrum, whereas the odd harmonic frequency components appeared in the case of using the square-like laser beams. Moreover, the SAW by the line-arrayed laser beam had narrower frequency bandwidth than the SAW by the single-line laser beam. These results were in good agreement with the theoretical predictions, which supports that laser-generated SAWs have the advantage of frequency modulation by modifying the spatial energy profile of a laser beam.