Spectral characterization and tuning with liquid-crystal retarders

An accurate characterization of the retardance function of liquid-crystal retarders (LCR) is essential for a proper use of instruments that include these devices. In this paper a simple technique to characterize the retardance of a LCR, both as a function of wavelength and applied voltage, is presented. With the proposed analysis we can describe the spectral modulation properties of the device using few parameters. The method is then extended to the case of non-normal incidence, thus allowing to distinguish between the extraordinary and ordinary axes. The accounting of Fabry-Perot interference effects are used to obtain a very accurate determination of the spectral phase shifts. Finally, such a full characterization of the LCR retardance is applied to a liquid-crystal spatial light modulator and an optical architecture is designed where the spectral content of the light beam can be engineered at will.