| 摘要 |
Markedly increased optical efficiency for a first diffraction order of incident wave energy, such as light, is derived from a layer of transparent material having effectively two serially spaced sinusoidal phase gratings of the same line spacing, each formed as a surface relief pattern thereon, by prescribing the thickness of the layer, the amplitude of the gratings, the respective indices-of-refraction of the layers and of transparent materials bounding the phase grating surfaces thereof, and the angle of incidence of the wave energy.
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