Focal plane masks for FOCAS polarimetryIn order to avoid blending of the ordinary and extraordinary rays, the standard masks for polarimetry have eight slits (or slots) of 10.0 mm = 20.6 arcsec length aligned at equal intervals of a 11.5 mm = 23.7 arcsec length gap (see figures). The standard masks are made of poreless ceramics (fluorine mica). The currently available masks are shown in the table.
(1) for longer wavelengths only (e.g., 300B+Y47)
Figure 1. Schematic representation of standard masks for spectropolarimetry
Figure 2. Schematic representation of standard masks for imaging polarimetry