The photonic spin Hall effect (SHE) in the reflection and refraction at an interface is very weak because of the weak spin-orbit interaction. Here, we report the observation of a giant photonic SHE in a dielectric-based metamaterial. The metamaterial is structured to create a coordinate-dependent, geometric Pancharatnam-Berry phase that results in an SHE with a spin-dependent splitting in momentum space. It is unlike the SHE that occurs in real space in the reflection and refraction at an interface, which results from the momentum-dependent gradient of the geometric Rytov-Vladimirskii-Berry phase. We theorize a unified description of the photonic SHE based on the two types of geometric phase gradient, and we experimentally measure the giant spin-dependent shift of the beam centroid produced by the metamaterial at a visible wavelength. Our results suggest that the structured metamaterial offers a potential method of manipulating spin-polarized photons and the orbital angular momentum of light and thus enables applications in spin-controlled nanophotonics. Keywords: geometric phase; metamaterial; photonic spin Hall effect INTRODUCTION Metamaterials or metasurfaces are artificial materials that are engineered to produce nearly any imaginable optical properties that are not found in nature. 1,2 They are typically structured at the subwavelength scale with ultrathin metallic or dielectric micro/nanoparticles or with holes opened in metallic films. Metamaterials exhibit unprecedented degrees of freedom in the polarization and phase manipulation of light via the geometric structuring of their structural units, especially on the wavelength scale, 3-9 which leads to applications such as vortex beam generators, 3,7 metalenses 10,11 and optical holography. 12,13 These materials also offer considerable potential for the manipulation of the angular moment of light and the photonic spin Hall effect (SHE), thereby providing convenient opportunities for spin-polarized photonics and nanophotonics. [14][15][16][17] The photonic SHE describes the mutual influence of the photon spin (polarization) and the trajectory (orbital angular momentum) of light-beam propagation, i.e., the spin-orbit interaction (SOI), which results in two types of geometric phases: the Rytov-VladimirskiiBerry (RVB) phase and the Pancharatnam-Berry (PB) phase. [18][19][20][21][22] The RVB phase is associated with the evolution of the propagation direction of light. When a light beam reflects/refracts at a planar interface between different media, a SOI occurs, and the corresponding momentum-dependent RVB phase leads to a spin-dependent real-

The recovery process of COVID-19 patients is unclear. Some recovered patients complain of continued shortness of breath. Vasculopathy has been reported in COVID-19, stressing the importance of probing microstructure and function of lungs at the alveolar-capillary interface. While CT detects structural abnormalities, little is known about the impact of disease on lung function. 129Xe MRI is a technique uniquely capable of assessing ventilation, microstructure and gas exchange. Using 129Xe MRI, we found COVID-19 patients have higher ventilation defects percentage (5.9% vs 3.7%), unchanged microstructure, longer gas-blood exchange time (43.5 ms vs 32.5 ms), and reduced RBC/TP (0.279 vs 0.330) compared with healthy subjects. These findings suggest regional ventilation and alveolar airspace dimensions are relatively normal around the time of discharge, while gas-blood exchange function is diminished. This study establishes the feasibility of localized lung function measurement in COVID-19 patients. Such readouts could be useful as a supplement to structural imaging.

Multifunctionalized and branched M-OEGs represent valuable PEGylation agents, linkers, and scaffolds in biomedicine. However, the tedious synthesis limited their availability and application. We herein present an azide reductive dimerization method for the convenient synthesis of aza-M-OEGs and derivatives, which provides easy access to a variety of multifunctionalized and branched M-OEGs in one step. With this method, hexa-arm M-OEGs with 54 symmetrical fluorines were synthesized in two steps as a water-soluble, self-assemble, 19F MRI sensitive, and biocompatible dendritic biomaterial.

We propose and experimentally demonstrate a novel interferometric approach to generate arbitrary cylindrical vector beams on the higher order Poincaré sphere. Our scheme is implemented by collinear superposition of two orthogonal circular polarizations with opposite topological charges. By modifying the amplitude and phase factors of the two beams, respectively, any desired vector beams on the higher order Poincaré sphere with high tunability can be acquired. Our research provides a convenient way to evolve the polarization states in any path on the high order Poincaré sphere.c 2014 Optical Society of America OCIS codes: (260.2110) Electromagnetic optics; (260.5430) Polarization.Light beam with spatially inhomogeneous state of polarization, also referred to as vector beam, has been investigated for many years due to its unique properties [1]. Comparing with the conventional homogeneous polarization represented by fundamental Poincaré sphere, the cylindrical vector beams can be represented by higher order Poincaré sphere (HOPS) [2][3][4]. Particular interests and investigations focused on the vector beams with radial and azimuthal polarizations, which can be represented as two points on the equator of the first-order Poincaré sphere. Such beams can be generated by twisted nematic liquid crystal [5][6][7], inserting phase elements in the laser resonator [8], computer-generated subwavelength dielectric gratings [9, 10], a conical Brewster prism [11], spatially variable retardation plates [12], and a binary phase mask [13]. The vector beams with special polarization symmetry can give rise to uniquely high-numericalaperture focusing properties that may find important applications in nanoscale optical imaging and manipulation [14][15][16][17][18][19].In this Letter, a novel interferometric method is proposed and experimentally demonstrated to generate arbitrary cylindrical vector beams on the HOPS. Homogeneous polarization on the fundamental Poincaré sphere can be seen as the superposition of two orthogonal circular polarizations corresponding to the two poles of the Poincaré sphere. Similarly, vector beams on the HOPS can be regarded as the linear superposition of two orthogonal circular polarizations with opposite topological charges. For homogenous polarization, two quarter-wave plates (QWPs) and one half-wave plate (HWP) with adjustable optical axis angles can transform it to any point on the fundamental Poincaré sphere [2]. For the HOPS, we use a modified Mach-Zender interferometer with which the amplitude and phase factors in each arm can be modified, respectively.In the parameter space of the HOPS, the state of polarization ψ ℓ can be represented by [3] Here, φ is the azimuthal angle and υ the polar angle in the spherical coordinate, respectively. L ℓ and R ℓ are orthogonal circular polarization vortexes with L ℓ = (x + iŷ)e −iℓϕ / √ 2 and R ℓ = (x − iŷ)e iℓϕ / √ 2, possessing spin angular momentum σ (σ = ±1) per photon where is the Plank constant. The factor e iℓϕ is the vortex phase associated with the orb...

Abstract:We present a simple and efficient method to generate any cylindrical vector vortex (CVV) beams based on two cascaded metasurfaces. The metasurface works as a space-variant Panchratnam-Berry phase element and can produce any desirable vortex phase and vector polarization. The first metasurface is used to switch the sign of topological charges associated with vortex, and the second metasurface is applied to manipulate the local polarization. This method allows us to simultaneously manipulate polarization and phase of the CVV beams.

Scheme 1. Synthesis of amino acids 2 and 3.

Novel pH-triggered nanoprobe were fabricated for (19)F MRI and fluorescence imaging (MRI-FI) of cancer cells. The biocompatibility, durability, high internalizing efficiency and pore architecture justify the Au-fluorescent mesoporous silica nanoparticles as ideal, highly sensitive and highly specific vectors for (19)F MRI and FI of cancer cells.

Both (19)F MRI and optical imaging are powerful noninvasive molecular imaging modalities in biomedical applications. To integrate these two complementary imaging modalities, the design and synthesis of a novel (19)F MRI/fluorescence dual-modal imaging agent is reported herein. Through Sonogashira coupling reaction between the fluorinated phenylacetylene and 1,2,4,5-tetraiodobenzene, a fluorophore with 48 symmetrical fluorines at its periphery was constructed with high efficacy. High aqueous solubility was achieved by PEGylation of the fluorophore with monodisperse PEGs. However, an unexpected self-assembly of the PEGylated amphiphilic fluorophore in water "turned off" the (19)F NMR signal. However, hydrogenation of the triple bonds or introduction of branched monodisperse PEGs was able to efficiently tune the self-assembly, resulting in the "turning on" of the (19)F NMR signal. One of these amphiphiles combines the advantages of label-free fluorescence, high (19)F MRI sensitivity, biocompatibility, and excellent aqueous solubility. The results demonstrate the great potential of such amphiphiles for real-time (19)F MRI and fluorescence dual-modality imaging.