An ultra-high-speed stokes polarimeter for astronomy

Optical polarization is a valuable diagnostic tool in astrophysics, frequently enabling asymmetries in source regions, magnetic field configurations, and magnetic field strengths to be investigated. In the context of high time resolution astrophysics polarimetry is particularly valuable in understanding the nature of the optical pulsations from pulsars, and whilst the averaged (over many cycles) linear polarization of the Crab nebula pulsar was determined many years ago, no attempts have been made to determine the Stokes vector of single, individual, pulse cycles. This may be very important information in the investigation into the nature of the enhanced optical pulses associated with random giant radio pulses. In the case of the Crab nebula this requires an instrumental response time of no more than 100 mu s, and, possibly, the capability of tagging individual photons with nanosecond resolution. This imposes certain constraints on the design of the polarimeter, which rules out all of the popular designs. We describe the design of a novel polarimeter which will be able to meet these constraints. This is based upon a design by Compain and Drevillon [1] in which their design is modified, by the use of a different glass and prism angles, to work over a wide bandwidth of 400-800 nm and with a high polarimetric efficiency.