1,720,988 research outputs found
Nematonics: from physics to photonics of reorientational solitons
No full textNematic Liquid Crystals are birefringent soft matter exhibiting unique nonlocal and nonlinear optical properties. Due to the interaction with finite-size light beams, self-focusing via molecular reorientation can balance out diffraction and result in self-confined beams, namely spatial solitons or nematicons, operating as waveguides for copolarized optical signals. Since nematicon propagation and confinement are determined by material properties that can be tailored by external fields, they allow implementing various photonic functionalities: from signal steering and addressing to bistability, from topological and optical symmetry breaking to beaming of random laser emission, to mention a few. Such proof-of-principle applications make nematic liquid crystals and nematicons a versatile platform for the study of complex light-matter interactions in nonlocal dielectrics and the demonstration of all-optical photonic devices for signal processing
Nonlocal soliton scattering in random potentials
No full textWe experimentally investigate the transport behaviour of nonlocal spatial optical solitons when launched in and interacting with propagation-invariant random potentials. The solitons are generated in nematic liquid crystals; the randomness is created by suitably engineered illumination of planar voltage-biased cells equipped with a photosensitive wall. We find that the fluctuations follow a super-diffusive trend, with the mean square displacement lowering for decreasing spatial correlation of the noise
Optical Detection of Dangerous Road Conditions
No full textWe demonstrated an optical method to evaluate the state of asphalt due to the presence of
atmospheric agents using the measurement of the polarization/depolarization state of near infrared
radiation. Different sensing geometries were studied to determine the most efficient ones in terms of
performance, reliability and compactness. Our results showed that we could distinguish between a
safe surface and three different dangerous surfaces, demonstrating the reliability and selectivity of
the proposed approach and its suitability for implementing a sensor
Power-controlled transition from standard to negative refraction in reorientational soft matter
No full textRefraction at a dielectric interface can take an anomalous character in anisotropic crystals, when light is negatively refracted with incident and refracted beams emerging on the same side of the interface normal. In soft matter subject to reorientation, such as nematic liquid crystals, the nonlinear interaction with light allows tuning of the optical properties. We demonstrate that in such material a beam of light can experience either positive or negative refraction depending on input power, as it can alter the spatial distribution of the optic axis and, in turn, the direction of the energy flow when traveling across an interface. Moreover, the nonlinear optical response yields beam self-focusing and spatial localization into a self-confined solitary wave through the formation of a graded-index waveguide, linking the refractive transition to power-driven readdressing of copolarized guided-wave signals, with a number of output ports not limited by diffraction
highly nonlocal optical response: benefit or drawback?
Full text linkA highly nonlocal optical response in space has been shown to heal several shortcomings of beam self-action in nonlinear optics. At the same time, nonlocality is often connected to limits and constraints in both temporal and spatial domains. We provide a brief and rather subjective review of what we consider the main benefits and some drawbacks of a highly nonlocal response in light localization through nonlinear optics, with several examples related to reorientational soft matter, specifically nematic liquid crystals
Observation of beam self-induced transition from positive to negative optical refraction in nematic liquid crystals
No full textWe demonstrate that light refraction at a straight interface between an isotropic dielectric and a nematic liquid crystal can change from positive to negative depending on power. The phenomenon relies on the reorientational response and the all-optical rotation of the optic axis, causing in turn variations in walk-off and beam self-steering
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