A submillimetre polarimeter for the continuum receiver UKT14 on the James Clerk Maxwell Telescope
The submillimetre continuum radiation from astronomical sources is often linearly polarised due either to the synchrotron radiation from relativistic electrons spiraling along magnetic field lines or thermal radiation from aspherical magnetically aligned dust grains. Measurements of the degree and direction of linear polarisation can yield useful and unique information on the physical conditions prevailing in the source and its environs. This thesis describes the development of a submillimetre polarimeter for the continuum receiver UKT14 on the James Clerk Maxwell Telescope (JCMT). The polarimeter is of the rotating half-wave plate design and the theoretical performance of such an instrument is considered under ideal and various non-ideal conditions. The mechanical, electronic and software systems engineered to convert this measurement concept into a useful instrument are detailed. High efficiency half-wave plates for submillimetre wavelengths were developed and their design, construction and testing is described. The results from extensive laboratory testing of the complete polarimeter are presented. Some general issues regarding polarisation measurement with UKT14 and the JCMT are considered before the observing methods used during the polarimeter commissioning tests at the JCMT are outlined. Successful submillimetre polarisation measurements were made on a variety of astronomical objects at 450μm, 800μm and 1100μm with many of these being first detections. In combination with UKT14 and the JCMT the polarimeter has achieved a significant increase in the available sensitivity and angular resolution of astronomical polarisation measurements at submillimetre wavelengths.