Patent ID: 8441650

Claim:
A grazing incidence interferometer comprising: a beam source section; a beam splitting section configured to split a beam from the beam source section into a measuring beam emergent to a measurement surface and a reference beam serving as a measurement reference, and configured to cause the measuring beam to emerge obliquely to the measurement surface; a beam combining part configured to combine the reference beam and the measuring beam reflected at the measurement surface, to obtain a combined beam; a detecting section configured to detect a profile of the measurement surface based on an interference fringe formed by the combined beam; and an image inverting part configured to invert an orientation of a wave front of the measuring beam or the reference beam, wherein: the beam splitting section causes the reference beam to emerge with an attitude in which the reference beam directly reaches the beam combining section; and the image inverting part is provided in an optical path of the measuring beam or the reference beam leading from the beam splitting section to the beam combining section, wherein: the image inverting part includes a dove prism formed with a cross-sectionally trapezoidal shape having equal base angles; and the dove prism refracts the beam incident on one end face thereof toward a bottom surface side thereof, and after reflecting the beam at the bottom surface toward another end face thereof, makes the beam from the other end face emergent along a direction identical to an incidence direction of the beam with respect to the one end face.