Circular Polariscope
In a circular polariscope setup two quarter-wave plates are added to the experimental setup of the plane polariscope. The first quarter-wave plate is placed in between the polariser and the specimen and the second quarter-wave plate is placed between the specimen and the analyser. The effect of adding the quarter-wave plate after the source-side polarizer is that we get circularly polarised light passing through the sample. The analyzer-side quarter-wave plate converts the circular polarization state back to linear before the light passes through the analyzer.
The basic advantage of a circular polariscope over a plane polariscope is that in a circular polariscope setup we only get the isochromatics and not the isoclinics. This eliminates the problem of differentiating between the isoclinics and the isochromatics.
Read more about this topic: Photoelasticity
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