A method for the construction of a graphite crystal polarimeter designed for measuring linear polarization of x-ray continuum sources is described. The dependence of reflected intensity upon the polarization direction of the incident beam at Bragg angles of 45° is used to measured the polarization. The particular instrument described was designed for a satellite x-ray polarimeter. By using a focusing parabolic surface instead of a nonfocusing flat crystal, the signal to background ratio is improved by a factor of 30 as compared to a flat crystal polarimeter of the same effective area. The focusing properties of the reflector were tested both optically and with x rays. The performance of the instrument as a polarimeter was tested with a continuum x-ray source of small polarization, which was independently measured by a single flat crystal polarimeter. The agreement between the two measurements is excellent, indicating that the instrument can measure polarizations as low as 0.3%.
Jayashree R. Toraskar, "Focusing crystal polarimeter designed for x-ray polarimetry: construction and performance," Appl. Opt. 14, 1727-1735 (1975)