Process for the production of lightfast phase holograms utilizing ammonium dichromate and gelatin as photosensitive recording material

Claim 1

A process for production of light fast phase holograms using a recording material comprised of a light-sensitive material containing hardenable gelatin in which the recording material is preliminarily hardened in a solution of 3-30% aqueous formaldehyde for up to 10 minutes to provide a temporary hardening and then sensitized in a solution of from 1-10% ammonium dichromate holographically exposed whereby cross-linked areas are created in accordance with the interference pattern of the holographic exposure and then the exposed material is developed to provide a phase hologram therein, wherein the improvement comprises the next treatment of the material after exposure is subjecting the hologram to a strongly basic formaldehyde sulfite bath comprising a solution of 3 to 20% by weight of sodium sulphite (Na 2 S 2 O 5 ) and 5 to 30% by weight of 30% formalin in water for a period to desensitize the ammonium dichromate sensitization of the recording material and then treating the desensitized material with a bath containing formaldehyde to harden the gelatin of the material and then irrigating with running water for 30 minutes to 1 hour to complete desensitization by washing out dichromate without altering the cross-linked condition in the gelatin, after which the exposed and developed material is dehydrated in a first stage with aqueous isopropanol solution and in a second stage with concentrated isopropanol solution to which formaldehyde has been added and dried, said process producing optically clear phase holograms having signal to noise ratios of 30 to 70.