Frequency response of narrowband surface waves generated by laser beams spatially modulated with a line-arrayed slit mask

Abstract

The objective of this study is to identify the frequency response of narrowband surface waves generated by a laser beam that has been spatially modulated with a line-arrayed slit mask. For theoretical analysis, the frequency response of the generated surface wave was modeled assuming that the energy distribution of each line beam was Gaussian. The variation in the frequency response according to slit opening width was predicted. However, experimental results generated by masking an expanded laser beam with line-arrayed slits were different from the theoretical predictions for wide slit openings. In this paper, we suggest a new model that assumes the energy distribution of each line beam to be uniform, which is a reasonable assumption when the slit mask is close to the surface of the specimen. The frequency response predicted by using this model showed good agreement with the experimental results over the entire range of slit opening ratios, which indicates that our uniform model is suitable for analyzing the frequency responses of narrowband surface waves generated by laser beams that have been spatially modulated with a line-arrayed slit mask.