ON THE ANGULAR SPREAD OF THE DEFLECTED SURFACE ACOUSTIC WAVE BEAM DIFFRACTED BY BRAGG GRATING

In this paper, basing on the equations of the deflection angle and of the deflection efficiency, the relation between the angular spread of the deflected SAW beam on the Bragg grating denoted by δθ₁, and the parameters of the grating is analyzed. A parameter referred to as 'Bragg width of the angular spectrum' of the acoustic grating is defined and it is designated with δθ_B. The meaning of the parameter δθ_B for distinguishing the angular spread range of the deflection beam is discussed as well. It is concluded from the analysis that if the spread angle of the incident beam (labelled with δθ_inc) is larger than the 'Bragg width of the angular spectrum' of the grating, the spread angle of the deflection beam δθ₁ will equal to δθ_B; On the contrary, if the angular divergency of the incident beam is less than δθ_B, then,δθ₁= δθ_inc.
Experimentally, 4 kinds of samples with different configuration patterns, 2 of which correspond to the regime of δθ_inc>>δθ_B, and the others correspond to the regime of δθ_inc<<δθ_B, are investigated by optical method. The width of the angular spread for incident beam and that for deflected beam are estimated by measuring the width of the acousto-optical diffraction point patterns. It is demonstrated that experimental results agree with theoretically expected results.