1. Field of the Invention
The present invention relates to interferometric measurement apparatus. More particularly, the invention relates to a method for aligning an interferometer.
2. The Prior Art
An interferometer is a basic instrument for optical metrology. The measurement accuracy of an interferometer depends on the accuracy of the alignment of the measurement and reference wavefronts to the optical axis. One prior art alignment method, described in my U.S. Patent, entitled "Optical Interferometer System with CCTV Camera for Measuring a Wide Range of Aperture Sizes", U.S. Pat. No. 4,201,473, issued May 6, 1980, is based on moving the television type images of two spots produced by the reference and measurement wavefronts, to the center of a television type image of an alignment reticle.
Prior art alignment methods may have some limitations, such as the operation of the alignment method being manual in nature and requiring an operator, or the method being subjective, depending on the operator's skill and judgment.
The present invention retains the basic viewing of the television type image of two alignment spots on a video monitor, however, the means used in the instant invention does not require the display of an alignment reticle and produces digital coordinates allowing automatic, objective alignment of the interferometer elements.