Patent ID: 6583931
Filing Date: 2003-06-24
Classification: G02B,G03F

Abstract:
A projection optical system comprising:at least one of a first optical member made of a silica glass and at least one of a second optical member made of a single crystal of calcium fluoride, wherein said at least one first optical member and said at least one second optical member are combined with each other so as to satisfy a placement condition such that a signed birefringence characteristic value of the entire projection optical system is in the range from âˆ’0.5 to +0.5 nm/cm, wherein said signed birefringence characteristic value of the entire projection optical system is calculated such that: a birefringence value is measured at a variety of points in a plane normal to an optical axis with a center at an intersection of each of said first and second optical members with the optical axis; and a distribution of signed birefringence values in each of said first and second optical members is obtained based on the birefringence values measured and a direction of a fast axis at each of the measured points, and wherein the signed birefringence characteristic value is calculated based on the distributions of signed birefringence values.