Patent ID: 9594253
Date: 2017-03-14
CPC Classifications: G01J,G01N,G02B

Claim:
1. An apparatus comprising: a slit that light enters; a first optical system configured to collimate the light from the slit; a transmissive type diffraction element configured to diffract the light from the first optical system; and a second optical system including a first mirror configured to reflect the light diffracted by the transmissive type diffraction element, and a second mirror configured to reflect the light reflected by the first mirror and diffracted by the transmissive type diffraction element, and configured to make the light reciprocally travel between the first mirror and the second mirror via the transmissive type diffraction element, wherein the first optical system and the transmissive type diffraction element are arranged such that an incident angle of the light that enters the transmissive type diffraction element equals an exit angle of the light that exits from the transmissive type diffraction element, the first mirror is arranged such that an optical path of the light diffracted by the transmissive type diffraction element and traveling toward the first mirror and an optical path of the light reflected by the first mirror and traveling toward the transmissive type diffraction element exist in one first plane without overlapping each other in the first plane, and the second mirror is arranged such that an optical path of the light diffracted by the transmissive type diffraction element and traveling toward the second mirror and an optical path of the light reflected by the second mirror and traveling toward the transmissive type diffraction element exist in one second plane without overlapping each other in the second plane.