HOLOGRAM DISK FOR PHOTOSCANNING

PURPOSE:To protect a hologram disk against mechanical scratching, unexpected striking, contacting, etc., and attain cost reduction by employing prescribed constitution for the hologram disk. CONSTITUTION:A hologram recording layer made of photoresist is formed on the reverse surface of the substrate 1 of the hologram disk 3, and plural diffraction grating facets are formed circumferentially by a two-luminous-flux inteference method. The surface of the disk 3 on which the diffraction grating 2 is formed is covered with a thin plate type cover 10. This cover 10 may be made of any material such as glass, plastic, metal, etc., but the plastic is suitable because of its workability, light weight, and strength. The cover 10 is joined to the substrate 1 with an adhesive or by a mechanical method. The cover 10 has a circumferential slit 11 which has such width that the passing of the incident light and refracted light of reproduced light is not inhibited. The reproduced light 5 is incident from below and the diffracted light 6 is transmitted through the transparent substrate 1 and projected upward to obtain scanning light.