In this paper, we aim to show that liquid crystal films (LCs) with well-defined molecular orientations are an exceptional platform for flat optical devices based on the Pancharatnam-Berry (PB) phase. Especially, the development of plasmonic photopatterning technique in recent years has made it easy to align liquid crystal molecules in to designer orientation patterns with both high spatial resolution and high throughput and thus enables large scale manufacturing liquid crystal optical devices with low costs. Here we present liquid crystal laser beam shapers and microlenses as two examples to illustrate the design principles and the fabrication processes for liquid crystal flat optical elements. In comparison with flat optical devices made of plasmonic or dielectric metasurfaces, liquid crystal flat optical elements are advantageous due to the high optical efficiencies and low fabrication costs.
According to our studies of polarization-sensitive materials based on azochromophores and polymers in recent years, a factor significantly influencing their photoanisotropic properties has been revealed. The degree of molecular integration of the material components (light-absorbing centers and polymer matrix) is in direct connection with the level of achievable birefringence in media obtained on their basis. This paper considers the results of a study of the integration of polarization-sensitive materials by means of molecular electrostatic forces. Experimental data of the photoanisotropic behavior of optical media based on advisedly designed organic chromophore salts with the participation of almost all alkali metals are shown. Lithium (Li⁺), sodium (Na⁺), potassium (K⁺), cesium (Cs⁺) and hydrogen (H⁺) are used as cations for these polarized light-receiver organic salts, and as an anion, on the other hand, is a residue of functional monoazo dye. The obtained light-absorbing organic salts are doped into the hydrophilic polymer matrix having good lyophilic compatibility. To study the induction of photoanisotropy in the obtained photosensitive materials, we investigate the effect of actinic polarized light on them with wavelengths of 445 nm and 532 nm and variation of reading wavelengths (at 532 nm and 635 nm) depending on the spectral characteristics of the test samples. Optimum parameters of exposure for each composition are determined experimentally. The kinetic curves of the induction of photoanisotropy in the new comparing polarization-sensitive media are shown as light-induced effective photoanisotropy for the various illumination conditions.
Transport of fluids and particles at the microscale is an important theme both in fundamental and applied science. We demonstrate how an advanced approach to photo-induced alignment of liquid crystals can be used to generate nonlinear electrokinetics. The photoalignment technique is based on irradiation of a photosensitive substrate with light through nanoaperture arrays in metal films. The resulting pattern of surface alignment induces predesigned 2D and 3D distortions of local molecular orientation. In presence of a static electric field, these distortions generate spatial charge and drive electrokinetic flows of the new type, in which the velocities depend on the square of the applied electric field. The patterned liquid crystal electrolyte converts the electric energy into the flows and transport of embedded particles of any type (fluid, solid, gaseous) along a predesigned trajectory, posing no limitation on the electric nature (charge, polarizability) of these particles and interfaces. The patterned liquid crystal electrolyte induces persistent vortices of controllable rotation speed and direction that are quintessential for micro- and nanoscale mixing applications.
We report for the first time the use of orientation dependent etching (ODE) of (110) c-Si in sidewall thin film technology for imprint mask fabrication with low line edge roughness (LER) over a large area. Oxidation is used for sidewall thin film formation with a good critical dimension control. 2-dimensional oxidation effects are discussed. Features down to 12 nm have been fabricated successfully. Simulation shows that the fabricated oxide line is strong enough to imprint both thermoplastic and photo-curable imprint resists.
We report our fabrication of nanoscale devices using electron beam and nanoimprint lithography (NIL). We focus our study in the emerging fields of NIL, nanophotonics and nanobiotechnology and give a few examples as to how these nanodevices may be applied toward genomic and proteomic applications for molecular analysis. The examples include reverse NIL-fabricated nanofluidic channels for DNA stretching, nanoscale molecular traps constructed from dielectric constrictions for DNA or protein focusing by dielectrophoresis, multi-layer nanoburger and nanoburger multiplets for optimized surface-plasma enhanced Raman scattering for protein detection, and biomolecular motor-based nanosystems. The development of advanced nanopatterning techniques promises reliable and high-throughput manufacturing of nanodevices which could impact significantly on the areas of genomics, proteomics, drug discovery and molecular clinical diagnostics.
Nano optical biosensors employ the interaction between biomolecules and light confined in nanometer scale structures to report the bio-recognition events. This small scale sensing area/volume can ensure that small amount of biorecognition events could be detected. The exceptional sensitivity and high spatial density of nano optical biosensors make them unique in practical applications in nucleic acid detection. Lab-on-a-Chip systems provide the capabilities of separation, cell lysing, polymerase chain reaction (PCR), allowing finishing bio agent detection processes on a chip. In this paper, we present our recent efforts on integrating some novel nanooptical biosensors into Lab-on-a-Chip systems and some preliminary test results.
Strong Raman signals have been observed in various molecules attached to rough metal film surfaces or nano silver/gold particles. This phenomenon is denoted as surface enhanced Raman scattering (SERS). Recent experiments have shown that the effective cross sections of Raman scattering can reach the same level that of fluorescence of good laser dyes, making SERS a promising single-molecular detection tool. The commonly used substrates for SERS consist of colloidal Ag/Au particle aggregates, where SERS active sites, called “hot spots”, are only found by chance and not controllable. The poor repeatability and controllability of these SERS substrates have prevented SERS from viable industrial applications, therefore it is imperative to design and fabricate optimized "hot spots" with desired plasmon resonance frequency in a controllable fashion. In this paper, we present a new class of composite nano particles, which is consisted of stacked alternative metal/dielectric layers, called nanoburger. We study optical properties of these nanoburger particles by using discrete dipole approximation method. The numerical results show that nanoburger particles possess many advantages over single layered particles, including high brightness or scattering intensity, high local field enhancements, and more freedom of tuning plasmon resonance wavelength. Another important merit of the nanoburger particles is that they can be fabricated with traditional micro/nano lithography techniques, and thus are integrable with techniques such as lab-in-a-chip.
Nano gold particles interact strongly with visible light to excite the collaborative oscillation of conductive electrons within nano particles resulting in a surface plasmon resonance which makes them useful for various applications including bio-labeling. In this paper, we study the effect of particle sizes with particle plasmon resonant wavelength and the coupling between pair of elliptical metallic disks and ellipsoid particles by simulations and experiments. The red-shift resonant peak wavelength of coupled particles to that of single particle is due to particle plasmons near-field coupling. The shift decays is approximately exponentially with increasing particle spacing, and reaches zero when the gap between the two particles exceeds about 2.5 times the particle short axis length. It is also found that the exponential decay of peak shift with particle gap is size independent but shape dependent.