Propagation Direction Of Incident Light Research Articles

Full-space-manipulated multifunctional coding metasurface based on "Fabry-Pérot-like" cavity.

Multifunctional coding metasurfaces (CMs) have attracted extensive attention due to their ability to realize the multifunctional integration in optical devices. However, the researches on multifunctional CM mainly focus on dual functionality in reflected or transmitted space. Here, based on "Fabry-Pérot-like" cavity, we propose a novel multifunctional CM to simultaneously control different polarized light in full-space. It is revealed that the designed CM possesses asymmetric transmission characteristic, which can simultaneously achieve three different functionalities by changing the polarization state and the propagation direction of incident light. As a proof of concept, a single CM is designed to simultaneously realize the functionalities of beam splitting, diffusion scattering for co-polarized reflection and beam focusing for cross-polarized transmission. The simulated results are consistent with the experimental results, which demonstrates the feasibility of the design. This finding provides an effective approach to design multifunctional devices with miniaturization and high integration, which can also be used to achieve desired functionalities in other frequency domains.

Optical properties of nanoporous silica frustules of a diatom determined using a 10 µm microfiber probe

A microfiber spectroscopic method was developed to reveal the photonic crystalline characteristics of a cylindrical frustule of the diatom Melosira variance. The spectroscopy apparatus used was composed of two quartz fibers with fine ends, approximately 10 µm in diameter, set on micromanipulators to control the position of the fine ends of each fiber, which were focused at the edge of a frustule. The method had fine space resolution and sensitivity toward the propagation direction of incident light, which is suitable for analyzing photonic crystallinity. A typical absorption was observed at wavelengths of 400–500 nm, which corresponded to a quasi-stop band calculated by a finite-difference time-domain (FDTD) method for a three-dimensional (3D) slab model constructed based on an SEM image of the frustule. These results suggest that the photonic crystalline characteristics of the frustule can assist the absorption of incident light near 420 nm, which is crucial for the efficient photosynthesis of the diatom.

Extrinsic 2D chirality: giant circular conversion dichroism from a metal-dielectric-metal square array.

Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

Backward emission angle of microscopic second-harmonic generation from crystallized type I collagen fiber

A theoretical model that deals with SHG from crystallized type I collagen fiber formed by a bundle of fibrils is established. By introducing a density distribution function of dipoles within fibrils assembly into the dipole theory and combining with structural order (m,l) parameters revealed by quasi-phase-matching (QPM) theory, our established theoretical model comprehensively characterizes both biophysical features of collagen dipoles and the crystalline characteristics of collagen fiber. This new model quantitatively reveals the 3-D distribution of second-harmonic generation (SHG) emission angle (θ,ϕ) in accordance with the emission power. Results show that fibrils diameter d(1) and structural order m, which describes the structural characteristics of collagen fiber along the incident light propagation direction has significant influence on backward∕forward SHG emission. The decrease of fibrils diameter d(1) induces an increase of the peak SHG emission angle θ(max). As d(1) decreases to a threshold value, in our case it is around d(1) = 150 nm when (m,l) = (1,0), θ(max) > 90 deg, indicating that backward SHG emission appears. The SHG may have two symmetrical emission distribution lobes or may have only one or two unsymmetrical emission lobes with unequal emission power, depending on the functional area of (m,l) on d(1).

High efficient optical focusing of a zone plate composed of metal/dielectric multilayer

We numerically investigate the optical field enhancement by a metal/dielectric multilayered zone plate. The optical field enhancement at the focal point of a zone plate originates not only from surface plasmon polaritons (SPPs)-assisted diffraction process along the propagation direction of incident light, but also from multiple scattering and coupling of surface plasmons (SPs) along the metal/dielectric multilayer films. By comparing multilayered zone plates to a conventional monolayered zone plate, we present the effects associated with the number of building blocks and different dielectric materials in the building block on the efficiency of the transmission.

Application of Mie theory to determine the structure of spheroidal scatterers in biological materials

We present here the results of a numerical study on light scattering from nonspherical particles with relevance to detecting precancerous states in epithelial tissues. In previous studies of epithelial cell nuclei, the experimental light scattering data have been analyzed by comparison with Mie theory. However, given the spheroidal shape of many cell nuclei, the validity of this assumption demands a thorough investigation. We investigate this assumption by using the T-matrix method to model light scattered from spheroids with parameters relevant to epithelial cell nuclei. In our previous studies, we have developed a data analysis procedure that extracts the oscillatory component of the angular-scattering distribution for an ensemble of epithelial cell nuclei for comparison with Mie theory. We demonstrate that application of our analysis procedure to the predictions of the T-matrix method for spheroids, oriented such that their axis of symmetry is aligned with the incident light propagation direction, generally yields the spheroid dimension that is transverse to the incident light propagation direction with subwavelength accuracy.

Enhanced Raman scattering by self-assembled silica spherical microparticles

A technique was developed to achieve enhanced Raman scattering of the silicon photon modes using closely packed micro- and submicron silica spherical particles. Investigation on the particle-size dependence of Raman enhancement revealed that the strongest enhancement occurs when the particle diameter is equal to the spot size of the incident laser beam. Calculations using the OPTIWAVE™ software based on the finite difference time domain algorithm under the perfectly matched layer boundary conditions were carried out. The results showed that photonic nanojets are formed in the vicinity outside the particles along the propagation direction of incident light. It was found that the nanojets are confined to a length of 100nm with a waist of 120nm. The presence of the strongly localized electromagnetic fields within the nanojets accounts for the enhanced Raman scattering. This technique has potential applications both in modern and traditional areas of surface science such as surface oxidation, adhesion, corrosion, and catalytic processes, and many other areas in biology, chemistry, materials science, and microelectronics.