Patent ID: 6366404
Filing Date: 2002-04-02
Classification: G02B,G03F

Abstract:
A projection optical system comprising at least two silica glass optical members, wherein said optical members are combined with each other so as to satisfy such a placement condition that a signed birefringence characteristic value of the entire projection optical system is between âˆ’0.5 and +0.5 nm/cm both inclusive, said signed birefringence characteristic value of the entire projection optical system being calculated in such a way that a birefringence value is measured at each of points in a plane normal to the optical axis with a center at an intersection of each optical member with the optical axis, a distribution of signed birefringence values in each optical member is obtained based on the birefringence values and directions of the fast axis thereof, and the signed birefringence characteristic value is calculated based on the distributions of signed birefringence values.