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Member Name: Thomas Ference
Title of Invention: Phase-Shifting Polarization Point-Diffraction Interferometer
Sales Link: http://www.engsynthesis.com/products_pdi.php
Email Address: tomcatofvt@aol.com
Street or P.O. Box: P.O. Box 5223
City: Essex Junction
State: VT
Zipcode: 05453

Description of Invention: The device couples the simplicity and stability of a point diffraction interferometer (PDI) with electro-optic phase modulation. The novelty of this interferometer lies in the innovative technique in which effective optical paths of the object wave and reference wave are separated by polarization. This polarization difference, generated by a diffractive feature in a half wave plate, is used in conjunction with an electro-optic phase modulator to dynamically shift the phase relationship between simultaneously generated object and reference waves.

The interferometer offers superior performance with a simple design. A single polarized beam is transmitted through a test system and imaged onto a modified half wave plate that generates two orthogonally polarized beams. A diffractive feature in the half wave plate generates a nearly perfect spherical reference wavefront through the fundamental process of diffraction. The remaining portion of the beam is transmitted through the wave plate and undergoes a 90° polarization axis rotation, while retaining the phase information of the test system. An anisotropic, electro-optic phase modulator introduces phase shifting between the two beams, which are recombined with a polarizer to produce an interferogram. This device is capable of generating high-precision interferograms with unity visibility. It can be adapted for applications from the ultraviolet to the infrared. Image capture of the phase-shifted interferograms with a CCD allows automated data reduction compatible with commercially available software packages.

This interferometer surpasses current state-of-the-art devices in size, speed, ease of alignment, cost, and environmental stability. This device is attractive for use in a wide range of commercial applications in the optical metrology market as it is robust, easy-to-use, has high-resolution, and is an affordable alternative to current interferometers.

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