Polarization Gratings: A Novel Polarimetric Component for Astronomical Instruments

Polarization gratings (PGs) have been recently been developed for ultraefficient liquid crystal displays, nonmechanical optical beam steering, and telecommunication devices at optical and near-infrared wavelengths (0.4–2.0 µm). A PG simultaneously acts as both a spectroscopic and polarimetric disperser for circularly polarized light. With the use of a quarter-wave retarder (or analog) to convert linearly to circularly polarized light, these devices can be used as linear polarimetric analyzers. PGs offer high throughput and high levels of birefringence and can currently be constructed inexpensively to diameters of 150 mm, and development projects are in progress to double that size. In this article we report on the characterization of a PG sample at mid-infrared wavelengths (2–40 µm), including the birefringence, throughput, spectral response, and cold cycling survivability. We discuss these devices in the context of astronomical polarimetry, especially as the polarimetric components for a conceptual study of a SOFIA-based polarimeter.