Complex refractive-index spectrum of liquid crystal in the infrared

The ordinary and extraordinary complex refractive indices, n(o) - j kappa(o) and n(e) - j kappa(e), of a nematic liquid crystal were measured in the infrared region at 3.0-11.5-microm wavelength. The complex refractive indices were evaluated in terms of the angular dependence of the reflectance. Semicylindrical CsI prisms and a goniometer were used for measurement of the reflectance in a wide incident-angle range and throughout the wide infrared spectral region. Refractive indices n(o) and n(e) changed notably near the absorption wavelength. Negative birefringence, i.e., n(e) < n(o), was observed in the vicinity of 6.6 microm, where n(e) changed more than did n(o).