PHOTOPOLARIMETER BASED ON PLANAR GRATING DIFFRACTION

A division-of-amplitude photopolarimeter (DOAP) is described that empl oys a diffraction grating in the conventional spectrometer orientation with the grating grooves normal to the plane of incidence. Four copla nar diffracted orders are used for polarimetric analysis to determine all four Stokes parameters of incident light simultaneously and virtua lly instantaneously (with the speed being determined solely by the pho todetectors and their associated electronics); a fifth order is used f or alignment by autocollimation or by use of a position-sensing quadra nt detector. To sensitize the instrument for the +45-degrees and -45-d egrees azimuths of incident linearly polarized light and for the hande dness of incident circular polarization (i.e., for the third and fourt h Stokes parameters), we insert two linear polarizers in two diffracte d orders with their transmission axes inclined at appropriate angles w ith respect to the plane of incidence. The calibration and testing of an instrument of this type that uses an Al-coated 600-groove/mm hologr aphic grating at 632.8-nm wavelength are reported as an example.