Formation of photonic liquid crystal metasurfaces on rubbed polyimide substrates patterned by focused ion beam is demonstrated. Modulation of the surface anchoring conditions with periods from 1 to 6 micrometers gives rise to periodic deformation of the nematic liquid crystal director field. The exact periodicity is confirmed by the light diffraction measurements. Distinct colors originating from the specific zero-order diffraction spectra are observed and qualitatively explained in terms of an analytical model within the one-constant approximation. Quantitatively accurate optical spectra are obtained by the full scale numerical simulations taking into account all relevant material parameters. The results pave the way for hybrid liquid-crystal-based metasurfaces with tunable optical transmission, diffraction, and lasing.

No abstract

No abstract

A bent-core mesogenic compound was used for preparation of thin solid Langmuir films (25-100 nm) that were transferred onto glass substrates and supplied with Al electrodes evaporated in vacuum. The Langmuir-Blodgett technique allowed us studying the thin polar films of the banana-shaped liquid crystal in sandwich geometry that keep amazing integrity on heating, even up to high-temperature B 2 phase, and show antiferroelectric and ferroelectric properties, which depend on film thickness. The magnitude of the measured switched polarization (400 nC/cm 2 ) is similar to that of the bulk material. The strong confinement of film results in high coercive field which reaches the value of 10 8 V/m for the thinnest film. The investigations of dielectric properties are reported.

No abstract

Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.

No abstract

No abstract