Attempts to increase the holographic exposure index of photographic materials

The holographic exposure index (HEI) relates the radiant energy necessary for recording a hologram to the diffraction efficiency to be achieved. In addition to the sensitometric speed of the recording material, the HEI takes into account that the modulation transfer function and macroscopic transfer characteristics, depolarization, and losses in the object beam path determine the share of the laser flux to be split off for the object beam. Several techniques expected to save exposure are examined. Extended development may increase the HEI by a factor of about 2, but light scattering due to granularity increases more. Combining a hologram exposure with incoherent preexposure or postexposure is governed by quite different characteristics, depending upon which of the exposures is variable or whether both are proportional. The characteristics alpha(E),beta(E) for amplitude holograms and gamma(E),delta (E) for bleached holograms are used for the analysis and verified experimentally. Preexposure or postexposure is of use only if extreme underexposure is unavoidable. When superimposing several holograms a decrease in diffraction efficiency in the order of exposure was found. Finally, Scientia 8E70 and 10E70 plates and 10E70 film were hypersensitized by bathing. Distilled water and a relatively diluted ammonia bath yield the best results by increasing both the sensitometric speed and the values of the macroscopic transfer characteristics, the gain in HEI becoming up to 3 for the slowest plate.