Organic volume phase holographic recording medium

In a medium for recording permanent volume phase holograms consisting essentially of a cured transparent polymer containing a soluble .alpha.-diketone being capable of intermolecular hydrogen atom abstraction and which has the formula ##STR3## wherein R and R' independently are selected from the group consisting of methyl, branched-chain alkyl and cyclic hydrocarbon groups wherein the carbon atoms are part of an aromatic or aliphatic ring and R and R' together can form part of an aromatic or aliphatic ring;

• and x is an integer of 1 or 2;
• and said .alpha.-diketone being present in an amount sufficient to cause a change in the index of refraction when illuminated by a spatially modulated coherent light beam having a wavelength corresponding to the absorption band wavelength tail of said .alpha.-diketone, the improvement which comprises:
• utilizing as said cured transparent polymer a vinyl benzene polyester polymer wherein said polymer is a reaction product of an unsaturated polyester and a vinyl benzene which has the formula ##STR4## wherein R" is a vinyl or an alkyl substituted vinyl group, R'" is a C.sub.1-5 alkyl group, n is an integer of 1-3, and m is an integer of 0-2;
• whereby sensitivity is increased.