Patent ID: 7081962

Claim:
A measuring apparatus for measuring the wavefront aberration of an optical system for a soft X-ray, comprising: a light source for supplying light of a predetermined wavelength within a wavelength range of 150 nm to 300 nm; a diffraction grating for diffracting the light from said light source; a first mask formed with a first opening of a size equal to or larger than the diffraction limit of said optical system, and a second opening of a size smaller than the diffraction limit of said optical system, said first opening being formed at a location at which a first diffracted light diffracted by said diffraction grating enters, said second opening being formed at a location whereat a second diffracted light differing in order from said first diffracted light enters; a second mask formed with a third opening of a size equal to or larger than the diffraction limit of said optical system, and a fourth opening of a size smaller than the diffraction limit of said optical system, said third opening being formed at a location whereat said second diffracted light passed through said optical system enters, said fourth opening being formed at a location whereat said first diffracted light passed through said optical system enters; and a detector disposed at a neighborhood of the conjugate plane of the pupil of said optical system; and wherein the wavefront aberration of said optical system is obtained on the basis of an interference fringe detected by said detector.