Photonic spin Hall effect:fundamentals and emergent applications

The photonic spin Hall effect(SHE)refers to the transverse spin separation of photons with opposite spin angular momentum,after the beam passes through an optical interface or inhomogeneous medium,manifested as the spin-dependent splitting.It can be considered as an analogue of the SHE in electronic systems:the light’s right-circularly polarized and left-circularly polarized components play the role of the spin-up and spin-down electrons,and the refractive index gradient replaces the electronic potential gradient.Remarkably,the photonic SHE originates from the spin-orbit interaction of the photons and is mainly attributed to two different geometric phases,i.e.,the spin-redirection Rytov-Vlasimirskii-Berry in momentum space and the Pancharatnam-Berry phase in Stokes parameter space.The unique properties of the photonic SHE and its powerful ability to manipulate the photon spin,gradually,make it a useful tool in precision metrology,analog optical computing and quantum imaging,etc.In this review,we provide a brief framework to describe the fundamentals and advances of photonic SHE,and give an overview on the emergent applications of this phenomenon in different scenes.

Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel

A kind of diamond grinding wheel bonded by short cast iron fibres has been developed. ln comparison with high quality bronze bonded diamond grinding wheel. the new wheel was more suitable to grind hard and brittle materials like ceramics. For Si3N4, the grinding efficiency has been raised two times and the grinding ratio five

Using endogenous glycogen as relaxation agent for imaging liver metabolism by MRI

Glycogen plays essential roles in glucose metabolism.Imaging glycogen in the liver,the major glycogen reservoir in the body,may shed new light on many metabolic disorders.^(13)C magnetic resonance spectroscopy(MRS)has become the mainstream method for monitoring glycogen in the body.However,the equipment of special hard-ware to standard clinical magnetic resonance imaging(MRI)scanners limits its clinical applications.Herein,we utilized endogenous glycogen as a T_(2)-based relaxation contrast agent for imaging glycogen metabolism in the liver in vivo.The in vitro results demonstrated that the transverse relaxation rate of glycogen strongly correlates with the concentration,pH,and field strength.Based on the Swift-Connick theory,we characterized the exchange property of glycogen and measured the exchange rate of glycogen as 31,847 Hz at 37°C.Besides,the viscosity and echo spacing showed no apparent effect on the transverse relaxation rate.This unique feature enables vi-sualization of glycogen signaling in vivo through T_(2)-weighted MRI.Two hours-post intraperitoneal injection of glucagon,a clinical drug to promote glycogenolysis and gluconeogenesis,the signal intensity of the mice’s liver increased by 1.8 times from the T_(2)-weighted imaging experiment due to the decomposition of glycogen.This study provides a convenient imaging strategy to non-invasively investigate glycogen metabolism in the liver,which may find clinical applications in metabolic diseases.

Giant photonic spin Hall effect in momentum space in a structured metamaterial with spatially varying birefringence

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.

Observation of tiny polarization rotation rate in total internal reflection via weak measurements

In this paper,we examine the tiny polarization rotation effect in total internal reflection due to the spin–orbit interaction of light.We find that the tiny polarization rotation rate will induce a geometric phase gradient,which can be regarded as the physical origin of photonic spin Hall effect.We demonstrate that the spin-dependent splitting in position space is related to the polarization rotation in momentum space,while the spin-dependent splitting in momentum space is attributed to the polarization rotation in position space.Furthermore,we introduce a quantum weak measurement to determine the tiny polarization rotation rate.The rotation rate in momentum space is obtained with 118 nm,which manifests itself as a spatial shift,and the rotation rate in position space is achieved with 38 μrad∕λ,which manifests itself as an angular shift.The investigation of the polarization rotation characteristics will provide insights into the photonic spin Hall effect and will enable us to better understand the spin–orbit interaction of light.

Photonic spin Hall effect on the surface of anisotropic two-dimensional atomic crystals

We examine the spin-orbit interaction of light and photonic spin Hall effect on the surface of anisotropic two-dimensional atomic crystals. As an example, the photonic spin Hall effect on the surface of black phosphorus is investigated. The photonic spin Hall effect manifests itself as the spin-dependent beam shifts in both transverse and in-plane directions. We demonstrate that the spin-dependent shifts are sensitive to the orientation of the optical axis, doping concentration, and interband transitions. These results can be extensively extended to other anisotropic two-dimensional atomic crystals. By incorporating the quantum weak measurement techniques, the photonic spin Hall effect holds great promise for detecting the parameters of anisotropic two-dimensional atomic crystals.

多核磁共振成像助力新冠肺炎疫情防控

新型冠状病毒肺炎(简称“新冠肺炎”)疫情在全球仍持续处于大流行阶段,目前全球范围内累积确诊病例超5亿。肺部和脑部损伤在新冠肺炎患者中最为常见,一些患者在出院后数周乃至数月仍有相关症状。医学影像技术在受累器官的结构和功能的诊断评估中发挥了重要作用。本文回顾了临床放射学在新型冠状病毒感染引起的肺部和脑部损伤评估中的应用现状,介绍了我们用于新冠肺炎预测与功能评估的新影像技术,进一步阐述了多核肺部磁共振成像原理及其在我国的发展,简述了基于我国自主研发的多核肺部磁共振成像装备对新冠肺炎患者肺部功能改变的定量可视化评估,以及对肺部和脑部损伤之间的关联研究。研究结果表明多核磁共振成像在新型冠状病毒致肺功能损伤评估中具有独特优势,可点亮传统影像的肺部“盲区”。

Weak-value amplification for the optical signature of topological phase transitions

We show that weak measurements can be used to measure the tiny signature of topological phase transitions.The signature is an in-plane photonic spin Hall effect,which can be described as a consequence of a Berry phase.It is also parallel to the propagation direction of a light beam.The imaginary part of the weak value can be used to analyze ultrasmall longitudinal phase shifts in different topological phases.These optical signatures are related to the Chern number and bandgaps;we also use a preselection and postselection technique on the spin state to enhance the original signature.The weak amplification technique offers a potential way to determine the spin and valley properties of charge carriers,Chern numbers,and topological phases by direct optical measurement.