Manufacture of diffraction gratings

In a method of manufacturing a diffraction grating, the grating-bearing surface of a master grating is coated with a release agent, and a rigid substrate has a layer of ultravoilet sensitive liquid resin applied thereto before bringing the master grating and the substrate together to trap a film of the liquid resin therebetween, whereafter the liquid resin is cured by exposure to ultraviolet light through the master grating and the master grating and resin-profiled substrate are separated prior to completion of the diffraction grating by deposition of a thin metal film on the resin-profiled surface of the substrate.