Interaction of whispering-gallery electromagnetic waves with acoustic waves in tapered quartz rods

The propagation of whispering-gallery waves in a dynamic cavity formed by a tapered quartz rod and the plane interface between two regions of the rod with different refractive indices moving along the axis of the rod is analysed. It is shown that the limiting frequency shift of light in such a cavity is determined by its Q factor and the attainable refractive index discontinuity. The possibility of using acoustic waves for obtaining a dynamic cavity is considered.