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1. (WO1998016799) INTERFEROMETER WITH CATADIOPTRIC IMAGING SYSTEM HAVING EXPANDED RANGE OF NUMERICAL APERTURE

Pub. No.:    WO/1998/016799    International Application No.:    PCT/US1997/018471
Publication Date: Apr 23, 1998 International Filing Date: Oct 15, 1997
IPC: G01B 11/255
Applicants: TROPEL CORPORATION
Inventors: VANKERKHOVE, Steven, J.
Title: INTERFEROMETER WITH CATADIOPTRIC IMAGING SYSTEM HAVING EXPANDED RANGE OF NUMERICAL APERTURE
Abstract:
A catadioptric imaging system for an interferometer includes a beamsplitter plate (52) for reflecting a beam of light to a concave mirror (46) for transmitting reflected light from the mirror. The beamsplitter reflections and transmissions produce opposite sign spherical aberrations. A refractive optic (74) is located between the beamsplitter plate (52) and a convex test surface (28) for removing residual spherical aberrations and for permitting more variability in the positioning of the beamsplitter plate (52). Design variables for both the refractive optic and the position of the beamsplitter plate can be used to adjust a numerical aperture of the beam approaching the test surface. The refractive optic can also be used as a Fizeau objective to further reduce errors in the imaging system.