Nonlinearities of photopolymer holographic recording materials

An analysis is presented of the nonlinear effects of holographically recording discrete image points on a phase recording material. The analysis is restricted to thin, two- and three-beam holographic gratings recorded on a material that exhibits a linear phase shift vs exposure. Harmonics, intermodulation noise, and small signal effects are considered. Experimental measurements were carried out for three-beam holographic gratings and diffuse object holograms recorded on photopolymer recording materials. Intermodulation noise is found to be a serious limitation for discrete image point holograms, because this noise cannot be spatially separated from the desired image points. Intermodulation noise can be reduced by increasing the reference-to-object beam irradiance ratio and by reducing the diffraction efficiency. Photopolymer gratings with 50-dB signal-to-intermodulation noise ratio were obtained with diffraction efficiency greater than 1/10% at beam irradiance ratios of 400:1. The image contrast of photopolymer holograms of diffuse objects is compared with the image contrast reported for bleached silver halide emulsions.