Dear All: I have recently encountered a small question regarding the determination of the degree of circular polarization of light. In an optical experiment, we are trying to create a circular polarized light beam by passing a HeNe-laser through a linear polarizer and a quarter wave plate (in which the fast axis is at 45 degree with the LP transmission axis). We need to determine 'the degree of circular polarization' of the output beam -the ratio between the intensity of the desirable circular polarization component in the output beam versus the intensity of the whole output beam. My intuition is placing another linear polarizer after the beam, and measure the overall transmission versus the rotation of the 2nd linear polarizer (in a 30 degree's step from 0 to 180 degree). We have the set of measured transmission, and they are very close but not exactly the same. Can I deduce the degree of circular polarization based on this data? Or else, could anyone give me a hint on how to measure and calculate it by other method? If possible, please provide a link of a published paper or a textbook that describes the calculation process, and I can study it in details. Thanks a lot! Best regards!