DIFFRACTIVE OPTICAL ELEMENT

摘要

The present invention provides a diffractive optical element having superi or optical characteristics. A polycrystalline substrate having crystal grains whose sizes are not mo re than 1 .mu.m or an amorphous phase at the dry-etched surface thereof, or an upper film layer 8 formed on a polycrystalline substrate 1 being the same materials as that of the polycrystalline substrate 1, which has finer crysta l grains than-those of the substrate. The upper film layer 8 is dry etched, an d AR coat 6 is formed thereon.