US 5,835,217 AGranted

Phase-shifting point diffraction interferometer

AssigneeThe Regents of the University of California

InventorHector Medecki

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Abstract

Disclosed is a point diffraction interferometer for evaluating the quality of a test optic. In operation, the point diffraction interferometer includes a source of radiation, the test optic, a beam divider, a reference wave pinhole located at an image plane downstream from the test optic, and a detector for detecting an interference pattern produced between a reference wave emitted by the pinhole and a test wave emitted from the test optic. The beam divider produces separate reference and test beams which focus at different laterally separated positions on the image plane. The reference wave pinhole is placed at a region of high intensity (e.g., the focal point) for the reference beam. This allows reference wave to be produced at a relatively high intensity. Also, the beam divider may include elements for phase shifting one or both of the reference and test beams.

Claims21

Dependent claims

A point diffraction interferometer comprising:

a test optic region at which a test optic is capable of being held;
a source of electromagnetic radiation located upstream of the test optic region and capable of producing a radiation beam directed toward a test optic region, such that an image is produced downstream from the test optic region at an image plane;
a beam divider for dividing said radiation beam into at least a reference beam and a test beam directed at different angles with respect to one another such that, when the test optic is held at the test optic region, the reference beam impinges at a first location on the image plane and the test beam impinges at a second location, laterally separated from the first location, on the image plane;
a phase shifting mechanism for adjusting the phase of at least one of the reference beam and the test beam;
a pinhole provided at the first location on the image plane such that radiation from the reference beam which passes through the pinhole produces a reference wave;
and
a detector located downstream from the image plane for detecting an interference pattern produced by combining the reference wave and a test wave provided from said test beam.

4 more elements

Dependencies are inferred from the claim text.