| 摘要 |
PURPOSE:To make a lowering of a reflectance in a region of center wavelength by increasing from a substrate side to an air side, the reflectance of the antireflection coating lying in the second layer among the three layers of the antireflection coating counting from the air side to the substrate side of the titled reflector. CONSTITUTION:MgF2 having the reflectance n1 of 1.30-1.45 ranges is used as the material forming the first layer 1 having the low reflectance, the mixture of ZrO2 and TiO2 having the reflectance n2 of 1.95-2.15 ranges is used as the material forming the second layer 2 having the high reflectance. The mixture of Al2O3 and CeF3 having the reflectance n3 of 1.60-1.80 ranges is used as the material forming the third layer 3 having the middle reflectance. The thicknesses n1d1-n3d3 of optical coatings in from the first layer to the third layer are n1d1=lambda0/4, n2d2=lambda0/2, and n3d3=lambda0/4 respectively. The reflectance of the transparent substrate B is 1.49-1.57. The coating C having >=0.02 the difference of the reflectances between the air side A and the substrate side of the titled reflector is used as the second coating whereby the reflectance lambda0 of the titled reflector in the region of the center wavelength depresses. |
