Optical
liquid-crystal metasurfaces self-assemble on polymer layers
locally processed with a digitally controlled focused ion beam. We
expand their functionality by introducing superperiodic design consisting
of parallel stripes of various widths inducing different liquid crystal
alignment. We optimize the design to achieve strongly asymmetric light
diffraction effectively resulting in efficient anomalous refraction.
By implementing the optimal patterns of different periodicity, assembling
a liquid crystal cell, and assessing its diffractive properties, we
experimentally confirm the deflection of normally incident light into
a particular oblique direction with 60% efficiency. Applying AC voltage
of several volts amplitude across the liquid crystal reversibly straightens
its orientation, suppresses the refraction, and reroutes light into
the direct transmission. Time-resolved measurements reveal that the
switching between refracting and transmitting states occurs within
a few milliseconds in both directions.
Self-assembling
of liquid-crystal metasurfaces on polymer layers patterned by a focused
ion beam manifests itself in distinctly colored optical transmission,
as light from certain spectral bands is efficiently diffracted by
the periodic liquid crystal modulations. We explore the metasurface
electro-optics by applying voltage across the liquid crystal to straighten
its director distribution and reroute the diffracted light into the
direct transmission. We show that the characteristic times of switching
from the diffracting to the transmitting state can be decreased down
to a millisecond by increasing the driving voltage up to 6–8
V, while the main part of the relaxation back into the periodically
deformed diffracting state occurs within about a few milliseconds,
i.e., by an order of magnitude faster than the relaxation of the analogous
homogeneous electro-optical liquid crystal cell. We explain the profound
dynamics in terms of superimposed exponential modes governed by an
interplay of the metasurface geometric parameters, the liquid crystal
viscosity, and elasticity.
We report on experimental investigations of the lasing effect in novel chiral liquid crystal (CLC) systems with a deformed lying helix (DLH). The lasing is studied for both odd- and even-order field-induced stop-bands, which are characteristic exclusively of the DLH state. The DLH state is achieved in special CLC cells with periodic boundary conditions, when the surface alignment is flipped between planar and vertical states. The alignment surfaces are prepared using focused ion-beam lithography. In an electric field, such CLC systems undergo an orientational transition, when the initial Grandjean-plane texture with the helix axis perpendicular to the CLC layer is transformed into the DLH state with the helix axis oriented in the plane of the layer. Due to field-induced strong deformation, the DLH system is characterized by a set of photonic stop-bands with a fine spectral structure; namely, on these fine-structured sub-bands, we have observed and studied the low-threshold lasing effect.
We report the formation of high optical power microlenses in the near-surface region of the liquid crystal layer. Such microlenses, possessing a very small focal length
f
at a rather large aperture A (
f
/
A
∼
2
), are able to focus the light into spots of a characteristic size comparable with the wavelength. Using numerical modeling, a specific patterning profile of a liquid crystal (LC) alignment surface by an ion beam is proposed to provide the aligning properties necessary for the formation of an array of microlenses with a focal length comparable to the LC cell thickness. The proposed microlens arrays are produced, and their optical properties are discussed.
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