Optical methods for precision measurements

Abstract

Contactless measuring techniques are becoming increasingly important for industrial applications . The use of a laser, solid-state detector arrays and powerful small computers leads to a very efficient fringe analysis in holography as well as in Moire and speckle techniques . Due to the computer analysis, much more information can be extracted from interferograms, leading to higher sensitivities and accuracies . The application of different fringe analysis procedures is discussed, together with some potentials of the application of interferometry, holography, and speckle and Moire techniques . . IntroductionInterferometry, holography, speckle and Moire techniques are becoming useful tools for precision measurements in research and for industrial applications . Computer analysis is increasingly important for fringe analysis . The use of solid-state detector arrays . image memory boards together with microprocessors and computers for the extraction of the information from the interferograms and high-resolution graphic hoards finds important application in optical metrology . Much more information can he extracted from the interferograms, leading to higher sensitivities and accuracies .Fringe analysis procedures including fringe peak detection and fringe order determination are tedious and time-consuming . Automatic fringe analysis and precision phase measuring techniques are very important in applying interferometric techniques . Automatic quantitative evaluation of interferograms requires accurate interference phase measurements . independent of fringe position and intensity variations superposed onto the interferograms . In many interferometric arrangements . phase shifting or heterodyne techniques have been introduced for automatic fringe analysis .In the phase shifting technique or quasi-heterodyne technique the relative phase is changed continuously or stepwise, using at least three phase shifts of 90° or 120°, for instance . The phase of the interference patterns can then he computed from the different measured intensity values . The phase shifting technique is very appropriate for digital processing and TV techniques . Interferometry and two-reference-beam holography together with video electronic processing lead to a sensitivity of 1 100 of a fringe at any point of the fringe pattern in the TV image . In heterodyne methods the relative phase increases linearly

Phase stepping: application to high-resolution moire

“…which is the result derived in a different way and with other notations by Bruning12 [9]. In the system we use, J3 = 6 and N = 16, which yields: = 0.0055 rad -io rad…”

Holographic Interferometry (HI), Infrared Vision and X-Ray Fluorescence (XRF) spectroscopy for the assessment of painted wooden statues: a new integrated approach

“…In order to integrate the SEM results shown in Figs respect to the ambient temperature [9], [10], [64]. In fact, due to the sensitivity to surface deformations, the technique can be used to gain meaningful information with regards to the structural characteristics of an artwork, by observing the surface movements produced when it is subjected to a mild stressing force.…”

Investigation of Weakly Oriented Polymeric Objects by Extended Fringe Field Interference Method

“…The variable-wavelength interferometry, which has been developed by many researchers, is one of the most successful approaches [1][2][3][4][5][6][7][8][9][10][11][12]. Pluta applied three different developed methods to determine the initial and current interference orders in the images of fringe field, uniform fringe field and optical Fourier transform of the highly birefringent under study [4,6].…”