System for measuring surface aberrations of concave cylindrical surfaces

Abstract

An improved system (30) for measuring surface aberrations of concave cylindrical surfaces. In the illustrative embodiment, the invention includes a transmission flat (20), an interferometer (32), and a surface to be measured (28). The transmission flat (20) is a transparent disc that is placed between the interferometer (32) and the surface (28) to be measured. An electromagnetic wave (33,34,36,37) is generated by the interferometer (32), and is directed through the transmission flat (20). The wave (41) bounces off the surface (28) to be measured and is retro-reflected off a first surface (26) of the transmission flat. The electromagnetic wave (42) returns to the opposite side of the surface (28) under test. The wave (43) then bounces off the surface (28) under test and passes through the transmission flat (20). The wave (43) interferes with light (39) that is reflected from a reference surface (26) of transmission flat (20) on a first bounce. Information contained in the interference pattern is used by the interferometer (32) to construct an image representative of the surface (28) to be measured. In a specific embodiment, a non-transparent strip of material (22) is disposed across the center of the transmission flat (20). The strip (22) prevents skewed light reflected off the measured surface from entering the interferometer (32) on the first bounce from the surface (28) under test, and blurring the image of the surface (28). In the illustrative embodiment, the transmission flat (20) has a reference surface (26) that reflects a portion of the electromagnetic wave (38,39) back toward the interferometer (32). The reflected wave (38,39) provides a reference for interferometer (32) calculations.

Dependencies are inferred from the claim text.