声表面波在声栅上的反常Bragg衍射

本文讨论了在考虑基片各向异性因素时,声表面波在声栅上的Bragg衍射现象。理论分析时,将有关波式和不同模式之间的差别唯象地以它们对应的相速不同来表征之,而不具体讨论这些波式或模式的偏振特性。在分析时,与讨论声-光反常Bragg衍射情形一样采用二波近似,但不借助于引入对应于极化矢量那样的量,而直接由栅区声速分布给出各波式之间的耦合系数。由此而得出的“反常Bragg衍射”公式,与声-光情形下采用极化矢量概念给出的公式一一对应。由这些公式计算的结果,与实验结果良好地符合。 关键词：

EXTRAORDINARY BRAGG DIFFRACTION OF SURFACE ACOUSTIC WAVE ON ACOUSTIC GRATING

In this paper, the Bragg diffraction of SAW on acoustic grating is investigated by incorporating the anisotropy of the substrates. In the analysis, the difference between the incident wave, the fundamental wave and spatial harmonic wave in grating region and the diffraction waves in transmission region is phenomenologically described by using their different corresponding velocities. The experimental results for the diffraction of SAW on acoustic grating which is fabricated on Y-cut LiNbO₃ are presented. The comparison of the experimental results with the analyzed results obtained on isotropy approximation shows that the discrepancy is significant. The "extraordinary Bragg diffraction" equations are obtained by using the coupled-waves method which takes the anisotropy of the substrates into consideration. It is shown that the calculated results based on "extraordinary Bragg diffraction" equations are coincident with the experimental results fairly well.