Dynamic phase-shifting electronic speckle pattern interferometer

Abstract

The technique for measuring changes in diffuse surfaces using Electronic Speckle Pattern Interferometry (ESPI) is well known. We present a new electronic speckle pattern interferometer that takes advantage of a single-frame spatial phase-shifting technique to significantly reduce sensitivity to vibration and enable complete data acquisition in a single laser pulse. The interferometer was specifically designed to measure the stability of the James Webb Space Telescope (JWST) backplane. During each measurement the laser is pulsed once and four phase-shifted interferograms are captured in a single image. The signal is integrated over the 9ns pulse which is over six orders of magnitude shorter than the acquisition time for conventional interferometers. Consequently, the measurements do not suffer from the fringe contrast reduction and measurement errors that plague temporal phase-shifting interferometers in the presence of vibration. This paper will discuss the basic operating principle of the interferometer, analyze its performance and show some interesting measurements.

Development of electronic speckle pattern interferometry for testing JWST composite structures

“…The optical layout of the interferometer is discussed in 9 . The test article is illuminated with a high power pulsed Nd:YAG laser operating at the second harmonic (532 nm).…”

“…The ESPI instrument discussed in this paper uses a simultaneous phase-shifting technique where the four phase-shifted interferograms are captured simultaneously in a single image 8,9 . This minimizes data acquisition time and allows accurate measurements in a high vibration test environment.…”

Dynamic surface roughness profiler

“…The primary advantage of the spatial phase measurement technique over temporal phase measurement is that only one image is required, allowing acquisition times several orders of magnitude smaller than in A novel approach to spatial phase measurement has been developed by 4D Technology Corporation called the pixelated mask spatial carrier method. [2][3][4] In this technique, the relative phase between the carrier and the test wavefront is modified on a pixel-by-pixel basis by a micro-polarizer phase shifting array placed just prior to detection. This technique has been successfully implemented in commercial vibration insensitive Twyman-Green and Fizeau interferometers with wavelengths from the infrared through UV.…”

Dynamic surface roughness profiler

“…[2][3][4] In this technique, the relative phase between the carrier and the test wavefront is modified on a pixel-by-pixel basis by a micro-polarizer phase shifting array placed just prior to detection. This technique has been successfully implemented in commercial vibration insensitive Twyman-Green and Fizeau interferometers with wavelengths from the infrared through UV.…”