MULTI-LAYER FILM TYPE DIFFRACTION GRATING

摘要

In order to increase the diffraction efficiency by forming a multi-layer film on a laminar type diffraction grating surface, it is necessary to satisfy four conditions: [1] condition of a groove depth capable of obtaining the optimal reflectivity; [2] extension Bragg condition of the multi-layer film; [3] condition expression defining correlation between directions of an incident light and a diffracted light; and [4] a ratio of the width of convex portion against the concave portion on the laminar type diffraction grating surface. However, there has been no unified design guideline. The present invention solves this problem by giving a general design guideline and an optimal multi-layer substance pair so as to provide a diffraction grating having both of a high diffraction efficiency and a high resolution in the wavelength region of 0.1 to 1 nm where spectroscopy using a diffraction grating is difficult because of the efficiency lowering.