| 摘要 |
PURPOSE:To prevent a drop in a function by heat generated when light is confined by a method wherein an area of a highly reflecting film of an etalon is constituted to be smaller than an area of a substrate on which the highly reflecting film has been formed. CONSTITUTION:A highly reflecting film 5 composed of a dielectric multilayer film is formed in such a way that it is larger than a passage cross-sectional area of a laser beam and is 60% or lower of an area of a substrate 1. When this etalon is used in an excimer laser apparatus, the highly reflecting film 5 is 60% or lower of a film formation face of the substrate 1 and is not formed in an outer periphery part, a reflectivity at the outer periphery face becomes small and light is quickly discharged to the outside of a system without being confined. That is to say, heat generated by inessential light and a thermal strain by it are reduced. In addition, since the film area is small, a strain by a stress at the inside of the film can be reduced as a whole. |
