Photoelastic-Modulator Polarimeters In Astronomy

Instruments used to detect polarized light from astronomical objects are briefly compared. Photoelastic-modulator polarimeters, introduced in 1970, have advantages particularly for extreme-sensitivity measurements of linear and circular polarization, down to the levels 0.01% and below. They have made possible several discoveries. Versions of such instruments for the u.v.-visible and for the infrared (1 - 13μ) are described.