Patent ID: 7379188

Claim:
A phase shift interferometer, comprising: an illuminating optical system for emitting a first polarized light and a second polarized light having polarizing directions orthogonal to each other or having rotating directions opposite to each other; a collimator lens positioned in an optical path between the illuminating optical system and a surface-to-be-measured; a reference half mirror positioned in the optical path between the collimator lens and the surface-to-be-measured for reflecting a portion of the first polarized light and the second polarized light while transmitting a portion of the first polarized light and the second polarized light toward the surface-to-be-measured; a pinhole plate provided with a pinhole located at a focus position of the collimator lens on the side opposite to the surface-to-be-measured; and a phase shift interference fringe acquiring section for making, in an object light reflected by the surface-to-be-measured and a reference light reflected by the reference half mirror, a portion of the object light and the reference light that have been passed through the pinhole interfere with each other in three or more different phases to acquire interference fringes with different phases; wherein in the first polarized light, the reference light reflected by the reference half mirror is passed through the pinhole while the object light reflected by the surface-to-be-measured is blocked by the pinhole plate; and in the second polarized light, the object light reflected by the surface-to-be-measured is passed through the pinhole while the reference light reflected by the reference half mirror is blocked by the pinhole plate.