Novel type of tunable infrared filters based on the Al2O3 particles – Liquid crystal system

The optical transmission of small aluminum oxide particles in liquid crystal 4-methoxybenzylidene-4′-butylaniline (MBBA) and dual-frequency liquid crystal mixture consisting of 4-n-pentyl-4′-cyanobiphenyl (5CB), 4-hexyloxyphenyl ester 4′-hexyloxy-3-nitrobenzoic acid (C2), 4-n-pentanoyloxy-benzoic acid-4′-hexyloxyphenyl ester (H 22) was studied. It was established that there was a transmission band which was shifted on application of a voltage and depended on temperature. At using the dual-frequency liquid crystal as a matrix, a transmission band maximum switched at changing of the frequency. The experimental results are explained by the optical homogeneity of the system in a narrow wavenumber interval when the refractive indices of the particle material and the matrix are close, and also by re-orientation of the liquid crystal molecules when a voltage is applied.The obtained results can be used in constructing of tunable filters and compact monochromators.

► The Al2O3 particles-liquid crystal system as a tunable filter.
► Dielectric anisotropy of dual-frequency liquid crystal depends on field frequency.
► A bandpass position depends on applied voltage, its frequency, and temperature.