POLICRYPS-based electrically switchable Bragg reflector

The formation and characterization of a switchable volume reflective element fabricated from a polymer liquid crystal (LC) polymer slice (POLICRYPS) structure by holographic photopolymerization at high temperature (65 °C) using a photosensitive/nematic liquid crystal prepolymer mixture is reported. The submicron Bragg structure formed consists of periodic continuous polymeric walls separated by periodic LC channels. The phase separated NLC self-aligns in a homeotropic alignment between the polymer walls as indicated by polarizing optical microscopy analysis (Maltese cross). The resulting periodic grating structure results in a Bragg reflection notch upon illumination with white light due to the periodic variation in refractive index. Electro-optical experiments realized through in-plane electrodes and temperature experiments confirm that the multilayer structure acts as a Bragg mirror whose reflection efficiency can be controlled by either a small (∼3V/μm) electric field or temperature

Control of the plasmonic resonance of a graphene coated plasmonic nanoparticle array combined with a nematic liquid crystal

We report on the fabrication and characterization of a switchable plasmonic device based on a conductive graphene oxide (cGO) coated plasmonic nanoparticle (NP) array, layered with nematic liquid crystal (NLC) as an active medium. A monolayer of NPs has been immobilized on a glass substrate through electrostatic interaction, and then grown in place using nanochemistry. This monolayer is then coated with a thin (less then 100nm) cGO film which acts simultaneously as both an electro-conductive and active medium. The combination of the conductive NP array with a separate top cover substrate having both cGO and a standard LC alignment layer is used for aligning a NLC film in a hybrid configuration. The system is analysed in terms of morphological and electro-optical properties. The spectral response of the sample characterized after each element is added (air, cGO, NLC) reveals a red-shift of the localized plasmonic resonance (LPR) frequency of approximately 62nm with respect to the NP array surrounded by air. The application of an external voltage (8Vpp) is suitable to modulate (blue shift) the LPR frequency by approximately 22nm

Thermoplasmonics with Gold Nanoparticles: A New Weapon in Modern Optics and Biomedicine

Thermoplasmonics deals with the generation and manipulation of nanoscale heating associated with noble metallic nanoparticles. To this end, gold nanoparticles (AuNPs) are unique nanomaterials with the intrinsic capability to generate a nanoscale confined light‐triggered thermal effect. This phenomenon is produced under the excitation of a suitable light of a wavelength that matches the localized surface plasmonic resonance frequency of AuNPs. Liquid crystals (LCs) and hydrogels are temperature‐sensitive materials that can detect the host AuNPs and their photo‐induced temperature variations. In this perspective, new insight into thermoplasmonics, by describing a series of methodologies for monitoring, detecting, and exploiting the photothermal properties of AuNPs, is offered. From conventional infrared thermography to highly sophisticated temperature‐sensitive materials such as LCs and hydrogels, a new scenario in thermoplasmonic‐based, next generation, photonic components is presented and discussed. Moreover, a new road in thermoplasmonic‐driven biomedical applications, by describing compelling and innovative health technologies such as on‐demand drug‐release and smart face masks with smart nano‐assisted destruction of pathogens, is proposed. The latter represents a new weapon in the fight against COVID‐19

Thermoplasmonics with Gold Nanoparticles: A New Weapon in Modern Optics and Biomedicine

Thermoplasmonics deals with the generation and manipulation of nanoscale heating associated with noble metallic nanoparticles. To this end, gold nanoparticles (AuNPs) are unique nanomaterials with the intrinsic capability to generate a nanoscale confined light‐triggered thermal effect. This phenomenon is produced under the excitation of a suitable light of a wavelength that matches the localized surface plasmonic resonance frequency of AuNPs. Liquid crystals (LCs) and hydrogels are temperature‐sensitive materials that can detect the host AuNPs and their photo‐induced temperature variations. In this perspective, new insight into thermoplasmonics, by describing a series of methodologies for monitoring, detecting, and exploiting the photothermal properties of AuNPs, is offered. From conventional infrared thermography to highly sophisticated temperature‐sensitive materials such as LCs and hydrogels, a new scenario in thermoplasmonic‐based, next generation, photonic components is presented and discussed. Moreover, a new road in thermoplasmonic‐driven biomedical applications, by describing compelling and innovative health technologies such as on‐demand drug‐release and smart face masks with smart nano‐assisted destruction of pathogens, is proposed. The latter represents a new weapon in the fight against COVID‐19

Advanced Diffractive MetaFilm Sailcraft

A fast-tracked multifaceted approach that integrated NASA, industry, and academia was successfully executed to advance the novel concept of radiation pressure by means of a thin diffractive film. This pioneering new approach to light sailing was found to offer advantages over reflective sails - especially for missions that include close orbits or a close fly-by of the sun.The research effort included experiments, numerical modeling, and an "incubator meeting" that brought together over 35 researchers and stakeholders to uncover some of the most feasible means of advancing both the TRL and mission capabilities of diffractive sailcraft. One of the outcomes of the incubator meeting was to focus this Phase I research on a solar polar orbiter mission for heliophysics experiments. NASA decadal surveys and other reports have repeatedly pointed out that scientists have only a paucity of information about the sun beyond the ecliptic plane. The TRL has been advanced from 1 to 3 during this Phase I research with the help of experiments that have verified the predicted force and mechanical control afforded by diffractive sails. Knowledge gained from the experiments and numerical models was not only disseminated in peer reviewed publications and conferences, but it also resulted in a patent disclosure

Broadband Vector Vortex Coronagraph Testing at NASA's High Contrast Imaging Testbed Facility

The unparalleled theoretical performance of an ideal vector vortex coronagraph makes it one of the most promising technologies for directly imaging exoplanets with a future, off-axis space telescope. However, the image contrast required for observing the light reflected from Earth-sized planets ($\sim10^{-10}$) has yet to be demonstrated in a laboratory setting. With recent advances in the manufacturing of liquid crystal vector vortex waveplates as well as system-level performance improvements on our testbeds, we have achieved raw contrast of 1.6$\times10^{-9}$ and 5.9$\times10^{-9}$ in 10% and 20% optical bandwidths, respectively, averaged over 3-10$\lambda/D$ separations on one side of the pseudo-star. The former represents a factor of 10 improvement over the previously reported performance. We show experimental comparisons of the contrast achieved as a function of spectral bandwidth. We provide estimates of the limiting error terms and discuss the improvements needed to close the gap in contrast performance required for future exoplanet imaging space telescopes.Comment: To appear in the Proceedings of the SPI

Orientational phenomena in liquid crystals on photorefractive substrates

The use of photorefractive liquid crystals (LC) and LC on photorefractive substrates for optical information processing applications is examined. The experiment used a homogeneously orientated nematic LC (NLC) sandwiched in a cell with hard anchoring of the director at the boundary layers. It was shown that the threshold value of the surface-localized electric field increases moderately, even if the field decreases inside the NLC exponentially. This makes the electrooptical phenomena in NLC possible under surface-localized influences

Thermodiffusive photorefractivity in liquid crystals

A breakthrough in the search for photorefractive materials occurred with the prediction and discovery of photorefractive liquid crystals (LC). Photorefractive LC solves two key problems: first, the voltage necessary to apply to the photorefractive material for realization of wave mixing is reduced from kilovolts to volts; and second, the modulation of the refractive index of the material can be as large as 0.2. The difference between the diffusion constants D+ and D- of photogenerated positive and negative ions is the reason for charge separation and space charge formation in the photoconductive LC

Surface-activated photorefractivity and electro-optic phenomena in liquid crystals

Surface-localized electromagnetic fields can induce strong reorientation of liquid crystals (LC\u27s), thus making it possible to observe a whole new class of opto-electronic phenomena. We show the feasibility of reorientation of a LC by a spatially inhomogeneous electric field localized on a photorefractive substrate. The modulation of the space-charge density in the plane of the photorefractive substrate generates a component of the electric field, which is normal to the LC layer. The drift of ions enforced by that field can result in a surface-charge modulation pattern that can become permanent owing to adsorption of ions at the boundaries of the LC cell. The obtained results present large fundamental and practical interest for the visualization of surface-localized electric fields and the development of new principles of optical information processing and storage. © 1998 Optical Society of America

Soret feedback in thermal diffusion of suspensions

We have theoretically studied the interaction of a light beam with liquids containing absorbing nanoparticles. We have shown that the Soret effect ensures a feedback that essentially limits heat insertion into the system and the change in its temperature: the temperature rise on the axis of a Gaussian beam is inversely proportional to the Soret constant. Transverse spatial redistribution of the absorbing particles gives a specific thickness dependence of the transparency of the material. These properties not only play an essential role in the study of light interactions with absorbing Solutions, but also can underlie optical methods for measurements of the Soret constant