Total absorption of unpolarized light by crossed gratings.

We present both experimental and numerical data showing the absorption of unpolarized, normally incident light by a gold crossed grating having a shallow sinusoidal profile. We show furthermore that the total absorption of unpolarized light can be achieved for an angle of incidence of 30 degrees with a crossed grating having its period adjusted appropriately from the normal incidence case to preserve the plasmonic resonance responsible for the enhanced absorptance. We contrast the process for achieving high absorptance in the principal plane of incidence aligned with the grooves of one of the gratings, with that for the principal plane at 45 degrees to each grating.

Blazed diffractive optics.

Diffractive optical elements with blazed profiles can, in theory, have 100% relative efficiency. We review several methods for making such elements and compare their advantages and limitations. Our emphasis is on processes to produce elements other than those with approximate, stepped surfaces, such as binary optical elements. For optical methods, we offer an expression relating the maximum numerical aperture of a diffractive lens with a given maximum efficiency to the numerical aperture of the recording system.

Variation of blaze of concave diffraction gratings.

The change in blaze wavelength as a function of position on a blazed concave diffraction grating surface is discussed. An experimental study of ruled and interferometric blazed concave gratings showed that the change in blaze across the grating surface is much less for an interferometric grating than for a ruled grating. Thus interferometric gratings can be expected to have a more uniform distribution of efficiency across their surfaces.