Reflecting diffraction grating for minimizing anomalies

In a reflecting diffraction grating comprising a plurality of grooves for light diffraction, each of said grooves being formed by first and second aluminum layers defining first and second reflecting surfaces, respectively, the improvement in that only a surface of said second aluminum layer has thereon a convex configuration formed by at least one evaporable material selected from the group consisting of aluminum, chromium, magnesium fluoride, silicon and germanium, said convex configuration preventing light reflected from the surface of said first aluminum layer from interfering with light reflected from the surface of said second aluminum layer and scattering thereat light reflected from the surface of said second aluminum layer, said convexly configured second reflecting surface having a surface roughness greater than said first reflecting surface thereby to reduce anomalies.

In a reflecting diffraction grating comprising a light reflecting supporting medium having a plurality of light reflecting grooves ruled in a surface thereof, the improvement wherein each groove consists of

• a first planar reflecting surface having first and second edges;
• a second planar reflecting surface one edge of which intersects the first edge of said first planar reflecting surface and the other edge of which intersects the second edge of the first planar surface of an adjacent groove, and
• a convex-shaped reflecting projection having a surface roughness greater than said first reflecting surface and extending from said second planar reflecting surface and having a first edge contiguous with said other edge of said second planar surface and a second edge intersecting said second planar surface at a location spaced apart from the intersection of said second reflecting surface with said first reflecting surface by the exposed planar portion of said second reflecting surface therebetween.