Complex Refractive-Index Spectrum of Liquid Crystal in the Infrared

The ordinary and extraordinary complex refractive indices, no - j?o and ne - j?e , of a nematic liquid crystal were measured in the infrared region at 3.0 -11.5- (mu)m 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 no and ne changed notably near the absorption wavelength. Negative birefringence, i.e., ne < no , was observed in the vicinity of 6.6 (mu)m, where ne changed more than did no .