Polarization Device For Improved Spectrograph Efficiency

Grating, and hence spectrograph efficiency, can be a strong function of the polarization of incident light. A polarization device has been designed to divide the light entering a spectrograph into two orthogonal polarizations, one of which is then rotated 90°, so that all of the light incident on the grating is polarized either parallel to or perpendicular to the grating grooves. Spectrograph throughput is thereby im-proved while also becoming independent of input polarization. Tests at the coude spectrograph of the Canada-France-Hawaii Telescope with an 830 f/mm grating revealed a 28% improvement in spectrograph throughput at a wavelength of 500 nm.