A polarimeter has been constructed by IRAM for measurements of circular polarization. It has been used on the telescope (see e.g. the March 1994 issue of the IRAM Newsletter). The main technical features of the polarimeter are briefly described below.
The polarimeter consists of a dielectric quarter-wave plate working in transmission. It is rotated between two positions at by a motor, the switching time is , and the phase time is adjustable. From the point of view of data acquisition, it functions like other switching devices, i.e. the chopper or the wobbler, and the difference between the RCP and LCP intensities is acquired.
The present quarter-wave plate has been designed for 113.3 GHz. Its transmission loss is %, and its cross-polarization below 20 dB. Similar plates could be fabricated for other frequencies if needed. Proposals for projects requiring the polarimeter can be submitted. They should clearly state the degree of technical performance that they demand. Besides the scientific evaluation, the acceptance and scheduling of such proposals will depend on their feasibility as judged from their requirements.