In recent years, there has been growing interest in the use of liquid crystals for modulation of IR radiation. One important application for IR modulators is the generation of dynamic IR scenes to test IR imagers.1 The 90° twisted nematic liquid crystal (TNLC) has been identified as a particular configuration candidate with which IR modulation via polarization rotation may be achieved.2 To assess the practicality of using the 90° TNLC configuration for IR modulation, we have conducted detailed measurements of the rotatory power of this type of cell over the 2–16-μm wavelength range. The rotatory power represents the basic modulation capability of a polarizer–LC cell-analyzer system. It is defined as the fraction of incident light intensity whose polarization has been rotated by 90° in passing through the liquid crystal cell. Thus, with a polarizer–TNLC cell-crossed analyzer arrangement, the rotatory power will be proportional to the transmission T through the analyzer. The experimental system consists of a wire grid polarizer-analyzer pair which are mounted with the TNLC cell in the cavity of a computer-controlled Fourier transform spectrometer.

© 1984 Optical Society of America

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