Photopolarimeter based on planar grating diffraction

Abstract

A division-of-amplitude photopolarimeter (DOAP) is described that employs a diffraction grating in the conventional spectrometer orientation with the grating grooves normal to the plane of incidence. Four coplanar diffracted orders are used for polarimetric analysis to determine all four Stokes parameters of incident light simultaneously and virtually instantaneously (with the speed being determined solely by the photodetectors and their associated electronics); a fifth order is used for alignment by autocollimation or by use of a positionsensing quadrant detector. To sensitize the instrument for the +45° and -45° azimuths of incident linearly polarized light and for the handedness of incident circular polarization (i.e., for the third and fourth Stokes parameters), we insert two linear polarizers in two diffracted orders with their transmission axes inclined at appropriate angles with respect to the plane of incidence. The calibration and testing of an instrument of this type that uses an Al-coated 600-groove/mm holographic grating at 632.8-nm wavelength are reported as an example.

Spectral polarization measurements by use of the grating division-of-amplitude photopolarimeter

“…At least 4 orders are measured, and at least 2 orders require that polarizers be placed in the beam paths. 7 The four detected orders provide four independent projections of the unknown Stokes vector of incident light, and measurements of the spectra of the 4 orders allow the incident polarization state to be determined as a function of wavelength. In Fig.…”

“…Other requirements for unambiguous detection of the complete polarization state when a G-DOAP is used are described in Ref. 7.…”

Dynamic acousto-optic photopolarimeter/spectrophotopolarimeter

“…Since at least four components are needed for complete polarimetry [16][17][18][19][20][21] and spectropolarimetry, 22,23 we select an AOD that operates in the Raman-Nath regime, where diffraction appears as a large number of diffracted orders. The grating is accurately described by the ''thin grating'' equation.…”

“…The AO photopolarimeter falls then under the class of the divisionof-amplitude photopolarimeters [16][17][18][19][20][21] ͑DOAPs͒, and is termed an AO-DOAP. This provides a moving phase grating that may diffract portions of an incident light into one or more directions.…”

Performance optimization and light-beam-deviation analysis of the parallel-slab division-of-amplitude photopolarimeter

“…The insertion of these linear polarizers in front of the detectors has been noted to increase the polarization sensitivity greatly. 12 The transmission axes of these polarizers are inclined with respect to the plane of incidence, which is the plane of the page in Fig. 1, by azimuth angles ͑␣ 0 , ␣ 1 , ␣ 2 , ␣ 3 , .…”