Optimization of a fixation-free rehalogenating bleach for BB-640 holographic emulsion

Abstract

Fixation-free rehalogenating bleaching is an interesting for the production of phase holograms. The shrinkage of the emulsion is reduced in comparison with other bleaching methods (reversal bleaching or rehalogenating bleaching with fixation). In this paper we present experimental results for fixation-free rehalogenating bleached holograms derived from the novel BB-640, a red-sensitive ultra-fine grain emulsion from Holographic Recording Technologies. The influence of the potassium bromide concentration in the bleach solution on the final quality of the holograms is also studied. The concentrations of the different components of the bleach solution are adjusted to obtain the highest values of diffraction efficiency. We show that really high diffraction efficiencies can be obtained, as high as 84%, when fixation-free rehalogenating bleached holograms are recorded on BB-640 plates.

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

“…On the other hand, Carretero et al [9] showed that the minimum transmission efficiency was found to be shifted in relation to the maximum diffraction efficiency when mixed gratings are recorded in the medium. It is interesting to note that Carretero et al investigated experimentally the response of transmittance in holograms recorded using procedures which typically produce absorption holograms, whereas in our study, we obtained mixed gratings when using a procedure which is known to produce pure phase gratings [11]. Because the holograms studied by Carretero et al were absorption holograms, the refractive index modulation achieved in their procedures was not high.…”

“…For instance, the degree of hardening of the gelatin coat of the emulsion is different for the three emulsions studied. The gelatin of BB-640 plates is hardened to a high degree [11], whereas the gelatin of Slavich PFG-01 plates is very soft [15]. These differences influence the temperature of the baths included in the processing.…”

“…For BB-640 and Agfa 8E75 HD plates the temperature of the bleach bath was maintained at 50˚C, whereas for Slavich PFG-01 plates it was necessary to lower the bleach bath temperature to 20˚C so as not to damage the gelatin of the emulsion. In the case of BB-640 plates [11], they were also hypersensitized by immersing them in a solution of distilled water with a sodium sulphite concentration of 1% and urea concentration of 5% (by weight) for 10 min at 20˚C. After rinsing in running water for 1 min at 20˚C the plates were dried for 24 h at 20˚C and 60% RH.…”

“…After exposure the plates underwent the schedule procedure in table 2 [11]. Two developers were used in order to determine the influence of the developer on the recording of mixed gratings: the D-19 developer, which is tanning, and the PAAP developer, which is non-tanning.…”

“…The ratio X = B/A indicates the relation between the potassium bromide concentration and the oxidizer concentration (potassium dichromate). The concentration of potassium bromide in the bleach bath determines the rate of the diffusion process [11]. A high rate of the diffusion process favours the refractive index modulation.…”