This paper describes a new method of separating only the isopachics of a birefringent object, the present eliminating the photoelastic effect of the object by using immersion method polarization holography. Further, the isochromatics can be also obtained from the isochromatic-isopachic fringe pattern without mutual interaction. Experimental results are given for a photoelastic model using air and water as the immersion media.
T. Kihara, H. Kubo, and R. Nagata, "Isopachics measurement using immersion method polarization holography," Appl. Opt. 15, 3025-3028 (1976)