Transmissive diffraction grating, and spectral separation element and spectroscope using the same

Abstract

A transmissive diffraction grating includes a substrate and a plurality of ridges provided in a mutually parallel manner at constant periodicity p on the substrate. The ridges include a first layer, a second layer (refractive index n2: 2.0-2.5), and a third layer with non-continuous refractive indices, arranged in that order from the substrate outward. The first layer adjacent the substrate, in terms of its refractive index, exhibits a difference of 0.1 or less relative to the substrate. The second layer has a higher refractive index than the first layer and third layer and satisfies the following conditions. For a single ridge, the cross-sectional area S of a cross-section of the second layer perpendicular to the longitudinal direction of said ridge is in the range of 0.75p2k1θ2/(n2−1)<S<1.20p2k1θ2/(n2−1), were, θ is the angle of incidence onto the diffraction grating face, expressed in radian units, and the constant k1 is 1.1. The thickness d2 of the second layer is in the range of 0.70pk2θn2/(n2−1)<d2<1.30pk2θn2/(n2−1), where, the constant k2 is 0.69.

Dependencies are inferred from the claim text.