| 摘要 |
PURPOSE:To reduce variation in transmission and reflection characteristics due to variation in angle of incidence by specifying the angles between the normals of the coating surfaces of dichroic mirrors and an optical axis. CONSTITUTION:The respective dichroic mirrors 2, 3, 12, and 13 and total reflecting mirrors 4 and 11 are so set that the angles between the normals P of the coating surfaces of the respective mirror and the optical axis are <=45 deg.. In this case, when light is transmitted through a film which has thickness (d) at the angle theta of incidence, a positional deviation determined by and constheta is generated, but the variation rate of a curve of costheta as its variable is relatively small when theta is <=45 deg. and large when >45 deg.. For the purpose, the angle thetaof incidence is set to <=45 deg. and the same coating film is usable within a range wherein the variation width of the costheta is small, thereby reducing the variation width of the transmission and reflection characteristics. |
