THE BIREFRINGENCE OF THE OPTICALLY NONLINEAR CRYSTAL 4-AMINO BENZOPHENONE

A precise method is presented for measuring the refractive index of an anisotropic prism with light polarized orthogonal to the prism axis w hich is also a dielectric axis. Prisms have been cut from crystals of the optically nonlinear 4-amino benzophenone with exceptionally low de fect concentration as identified by synchrotron white light topography . The linear refractive indices of these have been measured and fitted to four-parameter Sellmeier equations to an accuracy of 7x10(-6)-3x10 (-3). The values are accurately verified by observation of the externa l angle of incidence to a (001) plane required to meet the conditions of type-I phase matching with a fundamental wavelength of 1064 nm. The phase matching is of Hobden class six for this wavelength. In common with similar organic molecular materials, the molecular charge transfe r axis defines the most polarizable direction in the crystal, with the C=O direction being much less significant. (C) 1996 American Institut e of Physics.