A Wide Field, Low Light TV System to Measure the State of Polarization of Light

A low light level television system has been designed to measure the general state of polarisation of light. The instrument incorporates a portable television camera with a wide field of view (22 degrees vertical*29 degrees horizontal) which images the light transmitted by a rotating quarter wave plate and a stationary linear polariser combination. The data, stored on video tape, are analysed later using a video integrator to measure the variations in the light intensity at any point of the TV image from which the polarisation parameters of the incident light beam are determined. The principal advantage of this technique over other, more conventional, methods is that it enables spatial as well as temporal variations in the polarisation of the incident light to be measured. The system was developed to observe noctilucent clouds and proved to be capable of detecting small amounts of circular polarisation in an otherwise predominantly linearly polarised signal