High-speed imaging chopper polarimetry

The Stokes method provides a seminal method for the determination of the state of polarization of a beam of light using measurable quantities. This paper presents a methodology for the rapid acquisition of the four Stokes parameters. We have been able to acquire images at the rate of 500 images per second using a high-speed video camera. Using the camera, an optical chopper, a computer system containing a framegrabber, and software to coordinate all elements of the system, the four Stokes parameters have been acquired in 6 ms. Included in this paper is a description of all elements of the system, the calibration of the camera and polarization elements, the design of the imaging chopper polarimeter, and corrections related to rotation of polarization elements during exposure. A discussion of errors includes variations in pixel sensitivity, ill-conditioning of the Stokes parameters, aperture clipping, quasimonochromatic approximation, and variations in the Stokes parameters during data acquisition. Validation and testing of the methodology includes a comparison of empirical and theoretical skylight polarization parameters and values related to known, rapidly changing polarization states using several different bandwidth filters.