Abstract

Enhanced optical probing of surface acoustic waves (SAW) using stationary phase gratings in proximity to the SAW was found to be sensitive to the divergence of the probing laser beam. The sensitivity of the probing technique was seen to fall off as the separation between the stationary phase grating and the traveling SAW was increased. This gradual falloff was observed to increase as a function of the probing beam’s divergence.¹ This paper presents a theoretical analysis using generalized plane waves to include divergent Gaussian beams. The analysis shows the sensitivity of the technique to the probing beam divergence increases for higher frequency SAW. Experimental measurements using y-cut LiNbO₃ for z propagation were made for frequencies of 17.4 and 87.2 MHz corresponding to SAW wavelengths of 200 and 40 μm, respectively. The results of these experiments are shown for both frequencies at several beam divergences. Comparison of the calculated intensities for the 0 and ±1 orders of diffraction to the experimental results confirms the essential features of the analysis of the TEM₀₀ mode of a He-Ne laser.

© 1986 Optical Society of America