Transmission type diffraction grating, and spectroscopic element and spectroscope using the same

摘要

PPROBLEM TO BE SOLVED: To provide a transmissive diffraction grating which can be easily fabricated and can suppress deterioration in characteristics. PSOLUTION: The transmissive diffraction grating 100 includes a substrate 10 and a plurality of ridges 20 provided in a mutually parallel manner at constant periodicity p on the substrate 10. The ridge 20 includes a first layer 11, a second layer 12 (refractive index n2 is 2.0 to 2.5) and a third layer 13 with non-continuous refractive indices. The first layer 11 adjacent to the substrate 10, in terms of its refractive index, exhibits difference of 0. 1 or less relative to the substrate 10. The second layer 12 has a higher refractive index than the first layer 11 and the third layer 13 and satisfies the following conditions. For a single ridge 20, a cross-sectional area S of a cross-section of the second layer 12 perpendicular to the longitudinal direction of the ridge 20 is in the range of 0.75pSP2/SPkSB1/SBθSP2/SP/(nSB2/SB-1)S1.20pSP2/SPkSB1/SBθSP2/SP/(nSB2/SB-1), wherein θ is an incident angle onto a diffraction grating face, expressed in radian units, and the constant kSB1/SBis 1.1. The thickness dSB2/SBof the second layer 12 is in the range of 0.70pkSB2/SBθnSB2/SB/(nSB2/SB-1)dSB2/SB1.30pkSB2/SBθnSB2/SB/(nSB2/SB-1), wherein the constant kSB2/SBis 0.69. PCOPYRIGHT: (C)2008,JPO&INPIT