Digitally automated alignment of a phase-shifting point diffraction interferometer

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Montana State University - Bozeman, College of Engineering


Real-time sensing of wavefront error in laser instruments is an exceptionally useful tool for fine-tuning of laser systems during fabrication. Measurement and correction for potential wavefront aberrations are especially important for high-energy laser system applications, such as defense and industrial manufacturing. The self-referencing Mach-Zehnder interferometer and the Shack-Hartmann wavefront sensor are two common methods used to achieve real-time wavefront aberration measurements for laser system output quality; however, the former requires a precise and arduous alignment procedure for each operation and the latter exchanges spatial resolution for phase resolution and is highly sensitive to global tilt. The use of electronically controlled spatial light modulators has been shown as a method of quickly retrieving wavefront reconstructions from phase-shifting point diffraction interferometers. In this paper, the development of an algorithm that automates the selection of the point diffractor position and size was added to the phase-shifting point diffraction method with a purely reflective spatial light modulator. Computer simulations and laboratory tests were conducted as proofs of concept using a few simple optical elements. The results of these simulations and lab measurements show promise for continually automated alignment of a point diffraction interferometer to greatly reduce alignment time and almost entirely remove sensitivity to global tilt. With further development, this method can be applied to increase the efficiency of a wide variety of optical system measurement scenarios.




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