Patent ID: 8870383

Claim:
An optical member, comprising: a total reflection mirror including a reflection surface for reflecting a laser beam; a filter including a partially transmissive surface for passing therethrough a part of the laser beam and reflecting a remaining part of the laser beam, the partially transmissive surface being located so as to be opposed to the reflection surface; and a diffraction grating into which the laser beam enters, for diffracting the incident laser beam to enter the total reflection mirror or the partially transmissive filter, wherein: the total reflection mirror has an opening for causing the laser beam to enter the diffraction grating; the laser beam enters the opening so as to be perpendicular to the opening; a cross section of the laser beam has a major axis and a minor axis; and the diffraction grating diffracts the laser beam so that a ratio of a length of the minor axis to the major axis in the laser beam exiting from the optical member is larger than a ratio of the length of the minor axis to the major axis in the laser beam entering the diffraction grating.