High Efficiency Acousto-Optic Diffraction Into the Second Bragg Order

Abstract

Conventional Bragg diffraction devices operate in the first order with the light incident at the Bragg angle. Certain advantages would accrue, such as larger deflection angles and frequency shifts, if reasonably efficient operation c ould be obtained in the second order. In this comnunication we present both theoretical and experimental details of such a mode of operation with 70% efficiency and > 20% bandwidth. In 1976 Alferness’ analyzed the diffraction efficiency of thick holograms operating in the second order Bragg regime, with incidence angle equal to twice the Bragg angle. He concluded that 100% efficiency was possible for certain values of the hologram thickness. In so far as diffraction by a thick hologram is similar to acousto-optic diffraction by a rectangular sound column, a similar mode of operation ought to be possible for acousto-optic devices. Certain advantages would accrue from this such as a doubled frequency in frequency shifters and a doubled deflection angle in beam deflectors. this comnunication we report on such a mode of operation.