Polymer dispersed liquid crystal films for modulating infra-red radiation

The ability of thin films of polymer dispersed liquid crystals to operate as electro-optic devices for modulating infrared radiation between wavelengths of 1 and 5 μm has been investigated. The complex optical properties of the polymer component of the films, and the real component of the refractive indices of the liquid crystals, have been determined using a combination of transmittance spectroscopy and a Kramerʹs-Krönig dispersion relation utilizing reflectance spectra. The scattering characteristics of single droplets of liquid crystals have been determined and subsequently the contrast ratios of films have been calculated using an anomalous diffraction technique and compared with experimental values. Calculations of film contrast ratios demonstrate good correlation with experimental results for simple film geometries in the absence of multiple scattering. The agreement between experimental and calculated contrast ratios is shown to improve as the light mean free path through the films increases.