A: Output of a Prism (Black) B. Output of a 1200 g/mm grating in light polarized perpendicular to the grooves (green) C. Output of a 1200 g/mm grating in light polarized at 45 degrees to the grooves (red) D. Output of a 1200 g/mm grating in light polarized parallel to the grooves (blue) . Note: The efficiency curves of all gratings are different depending on blaze angle, groove density, or coating.  For ACTUAL efficiency curves - contact grating manufacturers. Conclusions Prism: Operates in refraction with no inherent change in light throughput as a function of polarization Polarization due to Fresnel reflection off prism surfaces can be significantly reduced, or eliminated, by anti-reflection coatings Grating Depending on the grating constants, diffraction efficiency can strongly depend on the polarization of incoming light.  All gratings are different so contact grating manufacturers to determine actual polarization dependence. Copyright © LightForm Inc, 2011 LightForm Inc: PARISS® Analytical Spectral and Hyperspectral Imaging Polarization Properties of Prisms and Diffraction Gratings Prisms are Polarization Independent Diffraction Gratings Tend To Be Highly Polarization Dependent  Plots Showing the Efficiency of a Prism and A Diffraction Grating As A Function of Polarization vs. Wavelength D C B A Diffraction Grating Theory and Practice The majority of diffraction gratings display significant polarization dependence as a function of wavelength.  The expected efficiency of a grating can be determined using electro-magnetic theory, and has been extensively described in the literature.  See the resources page for references. It is well beyond the scope of this web-page to describe grating and polarization issues in detail. However we can make some very general observations. Polarization depends on: • Refection or transmission: Most commercial spectrometers use reflection gratings  Application specific transmission gratings can offer less polarization sensitivity. • Groove density: the higher the number of grooves per mm (g/mm) the greater the polarization dependence. • Blaze angle: The larger the “blaze” angle the greater the polarization dependence.  See figure opposite. • Coating: Reflection gratings must be coated. In the visible this is almost always aluminum with a MgF₂  coating. • Operating geometry: Gratings are most efficient when used in Littrow.  Most spectrometers work off-Littrow resulting in changes in polarization sensitivity. • Holographic versus classically ruled.  Non-blazed holographic gratings are less polarization sensitive than truly blazed gratings.   Grating: 1200 g/mm; blaze 14 deg; at 400 nm Prism (Non-polarization dependent) 400 nm (Blaze) Grating and Prism Characteristics E_Parallel E_{perpendicular} E _45deg