US Patent 7304774 Holographic recording medium

A holographic recording medium 10 includes: a recording layer 12; two substrates 14 and 16 sandwiching the same; and a photosensitive protective layer 18 covering these recording layer 12 and substrates 14 and 16 entirely. The recording layer 12 is set so that its photosensitivity corresponding to a recording wavelength falls in the vicinity of the recording wavelength from shorter wavelengths to longer wavelengths. The photosensitive protective layer 18 is set so that its light transmittance corresponding to the recording wavelength falls in the vicinity of the recording wavelength from longer wavelengths to shorter wavelengths. This improves damage of the recording layer from ambient exposure without a drop in recording sensitivity.