Automatic two wavelength photoelasticimeter

摘要

An automatic two wavelength photoelasticimeter comprising, in succession, a light source for emitting light having at least two wavelengths, &lgr;.sub.1 and &lgr;.sub.2 ; a polarizer rotating at constant speed, an orientable quarter-wave plate of orientation &bgr; with respect to a reference axis; a model to be analyzed exhibiting double-refraction and having a fast axis which forms an angle &thgr; with respect to the reference axis and which provides a phase shift &phgr; (which parameters &thgr; and &phgr; are to be measured) and three photodetectors 5, 6, and 7 preceded by analyzers 10, 11 and 12 respectively. The photodetectors 6 and 7 are preceded by filters 8 and 9 of wavelengths &lgr;.sub.1 and &lgr;.sub.2 respectively. The difference between the phases of the signals of the frequency 2&ohgr; at the outputs of the photodetectors 6 and 7 supplies the difference between the phase shifts contributed by the model from these two wavelengths, the quarter- wave plate being oriented along the bisectors of the axes of double refraction of the model at the point in question. The apparatus is applicable to photoelasticimetry on strongly photoelastic materials and materiasl under high stress.