Abstract: An echelle grating having a groove facet angle and groove periodicity such that for laser-emitted light of two different wavelengths the highest propagating diffraction order is blazed and the next higher order is non-propagating such that the intensity of each blazed order is enhanced. In an example, the 84th diffraction order of a KrF excimer laser emitting at 248.4 nm and the 108th diffraction order of an ArF excimer laser emitting at 193.3 nm will both be blazed when the groove spacing d is 0.010623 mm, corresponding to a frequency f of 94.13 grooves per mm, and the groove facet angle .theta..sub.g is about 80.degree., whereas the next higher order for each laser, i.e., the 85th and 109th orders, respectively, are non-propagating, and thus both blaze orders are enhanced.

Abstract: An extra step for a conventional replica forming process for diffraction gratings used in lasers is described herein. Applicant has discovered that the deterioration of a replica diffraction grating, when used with intense laser light, is accelerated due to small quantities of the radiation leaking through minute fractures in the aluminum reflective coating. Applicant has identified the source of this problem as occurring during the removal of the replica from the master grating. Applicant's improvement to this conventional process is to deposit a thin reflective overcoat of aluminum on the surface of the replica after the replica has been removed from the master and cleaned. The overcoating is performed in a vacuum chamber by sputtering or evaporation. This overcoat is not subjected to any subsequent destructive forces and hence remains relatively opaque. A typical thickness of the overcoat is around 100 nm. An oxide layer is formed over the aluminum and a third layer of aluminum is formed over the oxide.