In the plane surface diffraction grating which is used for the conical diffraction oblique incidence

摘要

PROBLEM TO BE SOLVED: To perform an accurate spectrometry by deciding an expansion coefficient of a groove function of a series expansion formula indicating a groove pattern of a diffraction grating, so that a value of the expansion coefficient of an optical path function representing a focus of a spectral optical system containing the grating becomes substantially '0' in a wavelength within a wavelength range of wavelength scanning. ;SOLUTION: When a rotary angle θ of a diffraction grating 3 is '0', a light from an inlet slit 1 is reflected by a concave mirror 2 converted into a converged light, incident to a plane diffraction grating 3, diffracted, and focused at an outlet slit 4. A groove function constitutes a part of an optical path relation representing a distance from a point on the groove of the grating 3 to a focus F' of a diffracted light. Then, in order that a focal distance of the light becomes as constant as possible irrespective of a wavelength, the focal distance γ' and the expansion coefficient in the groove function are decided so that an expansion coefficient of the optical path function representing the focus becomes '0'.;COPYRIGHT: (C)2000,JPO