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Polarization gratings allow for real-time and artifact-free circular dichroism measurements

We propose a simple and innovative diffractive method for circular dichroism (CD) spectroscopy. It enables real-time measurements and suppress the artifacts introduced by anisotropic specimens and nonideal optical elements in conventional CD spectrometers. The method is based on a single cycloidal optical axis grating and takes advantage of its peculiar optical diffraction behavior. We prove that the true CD spectrum of a general anisotropic medium could be measured in the spectral range of interest, exploiting unpolarized white light and the intrinsic spectral selectivity of the grating. Two experimental approaches have been pursued to create the cycloidal optical axis grating, both based on polarization holography and liquid crystal photoaligning technology. The gratings are replicas of the polarization holograms in thin-films of azodyes, either in low molar mass liquid crystal cells or in reactive mesogen layers.