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Title: New algorithms for high accuracy phase shifting interferometry
Author: Farrell, C. T.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1993
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Phase shifting interferometry is a technique that allows the phase information of a wavefront to be calculated from several phase shifted interferograms. Traditionally this technique requires the use of at least three interferograms separated in phase by predetermined or equal amounts. The main problem limiting the technique's accuracy has been in accurately applying the required phase shifts. In this thesis the problem has been addressed by the derivation and application of new algorithms for phase step measurement and wavefront phase calculation. A novel method, utilising Lissajous figures and ellipse fitting, is described that uses the spatial information of the interferograms themselves to calculate the phase difference between interferograms, as well as their intensity bias and modulation. Two algorithms, referred to as A and B, are derived that use the information calculated in the ellipse fitting technique and do not need equal or predetermined phase steps. One of these algorithms can calculate wavefront phase from only two interferograms. A further two phase extraction algorithms in which step sizes need not be known or be equal are described. Both algorithms use Lissajous figures and ellipse fitting, but the ellipses are formed from temporal, rather than spatial, intensity profiles. The first algorithm, referred to as the inter-pixel algorithm, requires a minimum of five interferograms from which intensity offset and intensity modulation are calculated at each pixel and the relative phase is calculated for all pixels with respect to a reference pixel. The other algorithm, referred to as the dual-step algorithm, requires a minimum of ten interferograms and two phase stepping mechanisms, one of which must be absolutely repeatable. It also calculates intensity offset and modulation at each pixel but requires the use of algorithm A or B to do the final wavefront phase calculation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available