Patent ID: 6853450

Claim:
A monochromator comprising: an optical ray input section which limits the width of optical rays input from a light source, a first concave mirror for converting the optical rays passing through the optical ray input section into parallel rays, a diffraction grating for separating the parallel rays by wavelength into diffracted rays, a second concave mirror for condensing the diffracted rays when the diffracted rays are input, an optical ray output section which limits a wavelength band width of the condensed rays, and a substrate to which all of the optical ray input section, the first concave mirror, the diffraction grating, the second concave mirror, and the optical ray output section are fixed; wherein the first and second concave mirrors are formed of a first material and said substrate is formed of a second material different from said first material, a coefficient of linear expansion of a focal length of the first concave mirror, a coefficient of linear expansion of a focal length of the second concave mirror, and a coefficient of linear expansion of the second material forming the substrate are approximately the same.