Error analysis and correction of a photoelastic method based on a pixelated polarization camera

Abstract

The utilization of pixelated polarization cameras has brought a technical breakthrough to traditional photoelasticity method. In this paper, the principles of the new method are introduced. Then a few of systematic error factors, especially, the non-ideal polarization state of background light (it mainly refers to elliptically polarized incidence, but the stress birefringence of imaging lens was also counted in) and the low extinction ratio of the pixelated polarization camera are analyzed and evaluated. Finally, the corresponding algorithms for error removal are proposed. For the non-ideal polarization state of background light, we first determine its Stokes vector field, and then we obtain the phase retardance and polarization azimuth of the specimen by solving the equations describing relationship between the measured Stokes vector and the theoretical ones of the emergent light field of specimen. For the low extinction ratio of internal polarizer in the camera, we analyze the mechanism of how extinction ratio affects the measurement accuracy, and remove the measurement error by applying the degree of linear polarization (DoLP) of a standard quarter wave plate as the correction coefficient to be divided by the measured DoLP of the specimen. The effectiveness of correction algorithm is validated by some typical experiments, while reasons for the phenomenon that the errors were not completely eliminated are also remarked.