Point diffraction interferometer with enhanced contrast

摘要

The interferometer has a diffraction grating 21 , a condenser lens 22 , a transparent substrate 23 , a field lens 24 and an imaging device 25 arranged in this order. The transparent substrate 23 is arranged at the position in the optical axis direction where both focal spots of a zeroth-order diffracted light L 21 and a first-order diffracted light L 22 are formed. Formed on the transparent substrate 23 is a circular opaque zone 23 a whose central position is the central position of the focal spot of the first-order diffracted light L 22 . Formed at the center of the opaque zone 23 a is a pinhole 23 b whose central position is the central position of the focal spot of the first-order diffracted light L 22 . The contrast of the interference fringes observed on the image device 25 is enhanced by the optical interference between the first-order diffracted light L 22 passing through the pinhole 23 b and the zeroth-order diffracted light L 21 passing through the transparent substrate 23.