Integrated photoelasticity through imaging fourier polarimetry of an elliptic retarder.

It is shown that three optical parameters that are necessary for stress computation in integrated photoelasticity can be measured with high accuracy by use of a Fourier polarimetry method. Inasmuch as a photoelastic sample, which is an object of investigation in integrated photoelasticity, is a kind of an elliptic retarder, the technique presented here measures relative retardation delta, azimuth angle theta, and ellipticity angle epsilon instead of the characteristic parameters that traditionally have been used in integrated photoelasticity. The ability of the new technique to provide better accuracy with a simpler setup has been proved experimentally. Furthermore, the technique is self-contained as for phase measurement; i.e., it automatically performs phase unwrapping at the points where phase data exceed the value of pi. The full value of a phase at a certain point is retrieved by processing of pi-modulo phase data that have been precisely measured at several wavelengths. The usefulness of the new method for integrated photoelasticity has been demonstrated through measurement of a diametrically compressed disk viewed at oblique light incidence.