High-resolution birefringence imaging in three-dimensional stressed modelsby Fourier polarimetry

Recently several polarimetric techniques have been suggested, designed deli berately for automatic whole-field birefringence imaging in photoelastic mo dels with essentially three-dimensional stresses. In general, these techniq ues are feasible for mapping three optical parameters that determine birefr ingence in a given case. However, the difficulty in attaining a high level of data accuracy over the whole image persists. There remains a problem of precise imaging in regions where the mutual interference of three given par ameters inevitably causes accuracy deterioration. We show how to correct su ch imperfections in an imaging polarizer-sample-analyzer (PSA) Fourier pola rimetry technique, as suggested earlier [Appl. Opt. 41, 644 (2001)]. The gi ven technique (a method developed so that it maps the phase, the azimuth, a nd the ellipticity angles of an elliptic retarder) particularly fails to pr ovide precise imaging in regions where the phase is either close to null or approaches Tr-multiple values and in intervals where the ellipticity angle falls into the proximity of +/- pi /4 values. These drawbacks can be succe ssfully overcome by incorporation of a compensator into a PSA polarimeter a rrangement. Although use of a compensator in the polarimeter makes the orig inal technique more complicated, we demonstrate that the compensator allows two important issues to be resolved. First, it provides precise imaging fo r each of three optical parameters through the whole accessible intervals o f the parameters regardless of the absolute value of the parameter. In addi tion, it gives a sign of phase that remains undefined in the PSA techniques . Theoretical considerations are presented and are followed by experimental data that illustrate the improved accuracy capabilities of the compensator -enhanced technique. (C) 2001 Optical Society of America.