Refractive index modulation vs. before-bleach optical density modulation characteristics of silver halide phase holograms

A large number of plane-wave holograms were recorded in Agfa-Gevaert 8E75HD holographic plates, at a wide range of bias exposures and fringe visibilities. The plates were processed with various combinations of developers (AAC, Pyrogallol and Catechol) and bleaching agents (R-9 and EDTA). A pair of absorption and phase holograms was recorded at each value of the recording parameters. Optical densities before bleaching were determined using the absorption holograms. Then each phase grating was studied by phase-contrast microscopy, using a high-power immersion (100×) objective. Thus modulation of the refractive index as a function of the bias exposure and the visibility of the recording interference pattern could be determined. To characterize the processing, the modulation of the refractive index of the processed phase holograms was related to the amplitude of the optical density modulation obtained at the development step. These characteristics are especially useful for the comparison of various bleaching agents used with the same developer. Characteristics of similar forms were obtained for all the processing types, with significant differences in the slope and extent of the curves, so that sensitivity, linearity and dynamic range of the processes could be compared directly.