Acoustic diffraction in anisotropic gallium phosphide Bragg cells

The optically isotropic cubic crystal gallium phosphide (GaP) is a rich acousto-optic material because of its many efficient low attenuation, highly anisotropic acousto-optic modes. One shear mode, with acoustic propagation in the [1,-1,0] direction and polarization in the [0,0,1] direction, is particularly attractive for multichannel acousto-optic Bragg cell devices because of its anisotropic acoustic “self-collimating” beam property which allows individual channels to be closely spaced without the usual acoustical crosstalk due to acoustic diffraction. The optical beam propagation direction in this mode, however, can result in acousto-optic diffraction from the orthogonally polarized shear mode leading to unwanted acousto-optic diffraction and a subsequent reduction in the spurious free dynamic range of the acousto-optic device. We report here on the evaluation of the acoustic diffraction properties of other anisotropic acousto-optic modes in GaP