Effects of overmodulation in fixation-free rehalogenating bleached holograms

Abstract

The mechanism for hologram formation by fixation-free rehalogenating bleaching has been treated by several authors. Experiments carried out with Kodak and Agfa photographic plates have led to the conclusion that the transfer of material from the exposed to the unexposed zones is the main mechanism that drives the process. We show that when BB-640 emulsion is used in the recording of holograms by means of fixation-free rehalogenating bleaching, the mechanism for the transfer of material from exposed to unexposed zones is efficient enough to create high refractive-index modulations. We also comment on the overmodulation effects, which result in a decrease in diffraction efficiency.

Experimental evidence of mixed gratings with a phase difference between the phase and amplitude grating in volume holograms

“…This phase difference is due to the fact that the diffusion of silver halide grains takes place from the exposed to the unexposed zones. On the other hand, if bleaches with potassium dichromate are used in the procedure, another refractive index modulation, n h1 , could be stored in the hologram due to the differences in the degree of hardening between the exposed and non-exposed zones [13]. The refractive index created by this mechanism, n h , has the form:…”

“…This is because the hardening effect occurs when the ion Cr +6 is chemically reduced to Cr +3 during the bleaching bath [13]. This action takes place in the exposed zones, therefore the refractive index is in phase with the interference pattern recorded.…”

“…This diffusion process is particularly influenced by the halide concentration in the bleach solution [11]. Although fixation-free rehalogenating bleaches are generally known for creating pure phase holograms [9,[13][14][15][16], the oxidation products of the bleach can give rise to an absorption modulation at high values of exposure and high concentrations of potassium bromide in the bleach bath. Experimental confirmation of this fact can be found in reference [17].…”

Mixed phase-amplitude holographic gratings recorded in bleached silver halide materials

“…In two recent papers, we demonstrated that when the refractive index modulation is high the typical transmittance curves are not observed [13,14].…”