Patent ID: 7095510

Claim:
An interferometer comprising: beam splitting means for splitting an incident beam into first and second split beams; a first lens for converging the first and second split beams into first and second focal spots respectively; a transparent substrate that is arranged opposite to the first lens at a position on an optical axis direction adjacent to where the first and second focal spots are formed and having an opaque zone provided in a vicinity of a position where the second focal spot is formed, the opaque zone having a pinhole whose central position is a central position of the second focal spot; a second lens for converting a first divergent beam diverged from the first focal spot into a first parallel beam and for converting a second divergent beam diverged from the pinhole into a second parallel beam; and an imaging device for observing interference fringes produced by an optical interference between the first parallel beam and the second parallel beam, wherein the opaque zone formed on the transparent substrate has a disk shape.