Spatial Distribution Of Polarization Research Articles

Vector optical field with the polarization varying along an arbitrary circular trajectory on the Poincaré sphere.

As an inherent feature of vector optical field, the spatial distribution of polarization brings additional degrees of freedom to engineer the optical field and control the interaction between light and matters. Here we focus on the variation of polarization in single vector optical field, which can be defined by the trajectory on the Poincaré sphere. Based on the amplitude-phase-polarization joint modulation method we propose, vector optical field, whose variation of polarization follows arbitrary circular trajectory on the Poincaré sphere, can be generated. Moreover, the tightly focusing behaviors of the vector optical fields with the polarization varying along parallel circles on the Poincaré sphere are compared. Relations between the circular trajectory and the central intensity of the hollow focal field are concluded.

Trans-spectral vector beam nonlinear conversion via parametric four-wave mixing in alkali vapor.

Coherent frequency conversion of vector beams (VBs) without distorting their intensity profile or spatial polarization distribution is important for novel applications in quantum and classical regimes. Here, we experimentally and theoretically investigate VB transfer from near-infrared to blue light using a Sagnac interferometer, combining the parametric four-wave mixing process in atomic vapor. The vector probe beam is converted into a completely different wavelength, and the vector mode of the generated blue beam is highly similar to the incident probe beam. These results may provide a feasible solution for communication interfaces in classical and quantum science fields based on atomic ensembles.

Polarization-based intensity correlation of a depolarized speckle pattern

A different kind of intensity correlation, denoted as polarization-based intensity correlation (PBIC), is proposed and demonstrated to investigate the correlation between different polarizations of a depolarized speckle pattern (DSP), which has non-uniform spatial polarization distribution. It is shown both theoretically and experimentally that the range of the PBIC for any polarization of the DSP depends on the spatial average intensity of the speckles corresponding to that particular polarization. The experimentally determined nature of the change of the range of the PBIC for different polarization components, due to the variation in the average intensity, is found to be matching well with the theoretical prediction. The existence of non-zero correlation between two orthogonally polarized speckle patterns, filtered from a partially DSP, is also observed. This study may be useful in exploiting the PBIC for different applications such as speckle cryptography.

Flexosensitive polarization vortices in thin ferroelectric films

We present a theoretical study on the influence of the flexoelectric coupling on the spatial distribution and temperature behavior of the spontaneous polarization for several types of stable domain structure in thin ferroelectric films, such as stripe domains and vortices. Finite-element modeling (FEM) for ${\mathrm{BaTiO}}_{3}$ films and analytical calculations within the Landau-Ginzburg-Devonshire approach reveals that an out-of-plane polarization component can be very sensitive to the flexoelectric coupling for periodic quasi-2D stripe domains and 3D vortex-antivortex structures. However, the influence is rather different for these structures. The flexoelectric coupling increases significantly the amplitude of a small out-of-plane polarization component in the stripe domains, and the ``up'' or ``down'' direction of the component is defined by the sign of the flexoelectric coefficients. Concerning the vortex-antivortex pairs, their antivortices with in-plane anti\cyrchar\cyrs{}irculation have smooth wide dipolar cores through the entire film, whose shape and other features are almost insensitive to the coupling. The vortices with in-plane vorticity have spikelike cores with an out-of-plane quadrupolar moment induced by the flexoelectric coupling. The cores are located near the film--dead-layer interfaces. FEM results corroborated by analytical calculations prove that a change of the flexoelectric coefficient sign leads to a reorientation of the core axial polarization, making the flexosensitive 3D vortices similar to the recently introduced ``flexons'' in cylindrical nanoparticles. The relatively wide temperature range (from 200 to 400 K) of the flexosensitive vortices' existence gives us confidence that they can be observed experimentally in thin ferroelectric films by scanning-probe and nonlinear optical microscopy methods.

Modulation of coherence-polarization property of speckles using a birefringent scatterer.

The change of the spatial coherence-polarization (CP) property of a speckle pattern due to the modulation of birefringence in a scattering medium is investigated experimentally. The birefringence is introduced to the scattering medium by attaching layers of overhead projector (OHP) sheets to it. It is shown that the spatial polarization distribution can be tuned from a uniformly polarized case to a randomly polarized case by increasing the number of OHP sheets. The change of the spatial CP property with the number of OHP sheets is investigated from the study of the spatial degree of coherence and the degree of polarization, and these variations are further confirmed from the probability density function of the intensity of the speckle pattern and from the measurement of the generalized Stokes parameters. The effect of the change of the number of OHP sheets on the visibility of the intensity correlation function and the quality of the object retrieved through the scattering medium are also investigated.

Vortex beam array generated by a volume compound fork grating in lithium niobite

Here, we report a generation of vortex beam array based on a micro volume compound fork grating fabricated by a femtosecond laser direct writing technique in lithium niobite crystal. The grating is able to convert a Gaussian laser beam into an array of large number of vortex beams with high purity and high diffraction efficiency. The intensity distribution and the topological charges of the vortex beams are investigated, indicating there are multiple pairs of vortex beams with opposite topological charges in the array. Interference synthesizing method is also studied to superpose the opposite order vortex beams to produce integer-order vector-vortex beams, in addition to the generation of the fraction-order vector-vortex beam. The theoretical calculation and the experiment polarization measurement results indicate that the beams produced have spatial anisotropic polarization distribution. The micro structure of the compound fork grating has potential applications in generating vector-vortex beams in integrated optics field.

Intense high-order harmonic vector beams from relativistic plasma mirrors

Vector beam, with a spatial nonuniform polarization distribution, is important for many applications due to its unique field characteristics and novel effects when interacting with matter. Here through three-dimensional particle-in-cell simulations, we demonstrate that intense vector beams in the extreme-ultraviolet to x-ray spectral region can be generated by means of high harmonic generation (HHG) in the relativistic regime. The vector features of the fundamental laser beam can be transferred to the higher frequency emission coherently during the extreme nonlinear HHG dynamics from relativistic plasma mirrors. The vector harmonic beams can be synthesized into attosecond vector beams. It is also possible to generate vector harmonic beam carrying orbital angular momentum. Such bright vortices and vector light sources present new opportunities in various applications such as imaging with high spatial and temporal resolution, ultrafast magnetic spectroscopy, and particle manipulation.

Research progress of hybrid vector beams (Invited)

Polarization is an important property of light field. According to the spatial polarization distribution, optical field can be divided into the scalar field and the vector field. Since the vector field with inhomogeneous polarization distribution performs some interesting behaviors in light propagation, studying the vector beam is of either scientific significance or engineering applied importance. The hybrid vector beams, which contains all kinds of polarization state in the same wave front, has attracted a lot of interests since 2010. Due to the richer polarization states than the normal vector beam, the hybrid vector beam shows attractive prospect on the optical communication, optical manipulation and quantum communication fields. Here, the generation, focusing, propagating and nonlinear optics of the hybrid vector beam were summarized.

Coupling of heat flux and vortex polarization in superfluid helium

We consider a macroscopic description of the mutual influence between heat flux and vortex polarization in superfluid helium, in which the vortices produce a lateral deviation of the heat flux, and the heat flux produces a lateral drift of vortices. This coupling is a consequence of a microscopic Magnus force and mutual friction force between the vortices and the flow of excitations carrying the heat. We keep track of these effects with simplified macroscopic equations, and we apply them to second sound propagation between rotating concentric cylinders and to spatial distribution of polarization across a rectangular channel with vortices polarized orthogonally to the channel in the presence of an imposed heat flux.

Compact optical module to generate arbitrary vector vortex beams

We demonstrated a compact optical module that is capable of efficiently generating vector vortex beams (VVB). With this device, a linearly polarized input beam can be converted into a vector beam with arbitrary spatial polarization and phase distributions, accompanied by an energy utilization up to 61%. Equally important, the area utilization of the spatial light modulator, a key component in the device, is as high as 65.5%. With the designed vector-vortex-beam-generation module, several types of VVBs with different vortex topological charges and spatial polarization distributions were created experimentally. This device may find applications in optical tweezers, laser machining, and so on.

Modulate the vector beams with magneto optic effect in atomic ensembles

The ultimate challenge for shaping technology is how to control the light field with a single optical element in a high-speed manner, wherein the spatial distribution of amplitude, phase or polarization are manipulated. Here we describe the use of the magneto optic effect to achieve the rapidly shaping of vector beams in real time using atomic ensemble. Firstly, the Faraday-rotation effect of vector beams is shown. On this basis, dynamically modulate the polarization of a vector beams on each point is implemented, and the polarization state of the manipulated beam is characterized with spatially resolved Stokes parameters measurements. The response time of this manipulation is about 40 μs. The magnetic field high-speed switching and the dynamic manipulation capabilities of this method will be particularly useful for controlling light propagation through complex media and speed up the measurement of the properties of media.

Machine-Learning Analysis to Predict the Exciton Valley Polarization Landscape of 2D Semiconductors.

We demonstrate the applicability of employing machine-learning-based analysis to predict the low-temperature exciton valley polarization landscape of monolayer tungsten diselenide (1L-WSe2) using position-dependent information extracted from its photoluminescence (PL) spectra at room temperature. We performed low- and room-temperature polarization-resolved PL mapping and used the obtained experimental data to create regression models for the prediction using the Random Forest machine-learning algorithm. The local information extracted from the room-temperature PL spectra and the low-temperature exciton valley polarization was used as the input and output data for the machine-learning process, respectively. The spatial distribution of the exciton valley polarization in a 1L-WSe2 sample that was not used for the learning of the decision trees was successfully predicted. Furthermore, we numerically obtained the degree of importance for each input variable and demonstrated that this parameter provides helpful information for examining the physics that shape the spatially heterogeneous valley polarization landscape of 1L-WSe2.

Spatial phase and polarization retrieval of arbitrary circular symmetry singular light beams using orthogonal polarization separation.

Circular symmetry singular light beams (CS-SLBs) possessing spatially variant field distributions have drawn extensive attention because of their unique optical properties. However, the extraction of spatial phase and polarization distributions is always a significant but difficult issue in CS-SLB applications. Here, we propose and experimentally investigate an orthogonal polarization separation (OPS) method to retrieve the spatial phase and polarization distributions of arbitrary CS-SLBs. Theoretically, the CS-SLB, including the vortex beam (VB), cylindrical vector beam (CVB), and cylindrical vector vortex beam (CVVB), can be decomposed into two orthogonal circularly polarized sub-VBs. Therefore, once the spatial phase distributions and initial phase difference of the two components are obtained, the phase and polarization distributions of the CS-SLB can be retrieved, and its type can also be identified. Based on this analysis relationship, we first separated the CS-SLB into two circularly polarized sub-VBs and designed an astigmatic phase iterative algorithm to restore their spatial phase information. After retrieving the phases of the two components, we have experimentally obtained the spatial phase and polarization distributions of three typical CS-SLBs, including VBs, CVBs, and CVVBs. These results demonstrate that this method provides a feasible way to retrieve the variant field distributions of CS-SLBs and may have great application prospects in optical imaging, optical communication, etc.

Arbitrary Cylindrical Vector Beam Generation Using Cross-Polarized Modulation

Due to the spatial non-uniform distribution of polarization, cylindrical vector beam (CVB) shows many superior properties and has drawn many research interests. In this letter, we propose and investigate a cross-polarized modulation method to generate the stable CVBs with arbitrary state on the high-order Poincare sphere (HOPS). It demonstrates that the CVB can be decomposed into a left-handed and a right-handed circularly polarized vortex beam. Exploiting the polarization sensitivity of spatial light modulators (SLMs), the spatial spiral phases are modulated to the horizontal and vertical parts of the linearly polarized beam to produce the CVB. By manipulating the phase difference between the two orthogonal-polarized components, the CVBs with arbitrary rotation at the equator of HOPS are experimentally obtained. These results indicate that the cross-polarized modulation method may provide a simple and flexible way to generate the CVBs with arbitrary polarization states and high stability.

Absolute 1H polarization measurement with a spin-correlated component of magnetization by hyperpolarized MAS-DNP solid-state NMR

Sensitivity of magic-angle spinning (MAS) NMR spectroscopy has been dramatically improved by the advent of high-field dynamic nuclear polarization (DNP) technique and its rapid advances over the past decades. In this course, discussions on ways to improve the DNP enhancement factor or the overall sensitivity gain have been numerous, and led to a number of methodological and instrumental breakthroughs. Beyond the sensitivity gain, however, discussions on accurate quantification of the 1H polarization amplitude achievable in a sample with DNP have been relatively rare. Here, we propose a new method for quantifying the local 1H hyperpolarization amplitude, which is applicable to un-oriented/powdered solid samples under MAS NMR conditions. The method is based on the ability to observe the high-order spin-correlated term (2IzSz) intrinsic to a hyperpolarized IS two-spin state, separately from the lowest-order Zeeman term (Sz) in quasi-equilibrium magnetization. The quantification procedure does not require evaluation of signal amplitudes for a “microwave-off” condition and for an un-doped reference sample, and thus enables quick and accurate quantification unaffected by the effects of the paramagnetic quenching and the MAS-induced depolarization. The method is also shown to elucidate spatial polarization distribution through the 2IzSz term prepared domain-selectively. As a potential application, we also demonstrate 2D DQ-SQ spectroscopy utilizing the 2IzSz term that is generated in a spatially selective manner without using IS dipolar or J coupling. These salient features may be evolved into a way for characterizing mesoscopic molecular assemblies of medical/biological importance.

Diffraction-limited near-spherical focal spot with controllable arbitrary polarization using single objective lens.

We report a time-reversal method based on the Richards-Wolf vectorial diffraction theory to generate a diffraction-limited near-spherical focal spot with arbitrary three-dimensional state of polarization using single objective lens. Three orthogonal dipole antennae are positioned above a flat mirror at a prescribed distance and an aplanatic objective lens is utilized to collect all the radiation fields emitted by the dipole antennae. The optical field in the pupil plane is calculated in a time-reversal manner and the vectorial Debye integral is used to verify the spatial intensity and polarization distributions in the focal region. The ability to confine the optical power within a subwavelength near-spherical volume with controllable three-dimensional polarization with single objective lens may be exploited in high-resolution imaging, high-density data storage, laser direct writing, lithography, spin-directional coupling, anisotropic particle trapping and manipulation.

Nanoscale Polarization Manipulation and Encryption Based on Dielectric Metasurfaces

AbstractManipulating the polarization of light is highly desired for versatile applications ranging from super resolution, optical trapping, to particle acceleration. The enormous freedom in metasurface design motivates the implementation of polarization control in ultrathin and compact optical systems. However, the majority of proposed strategies based on metasurfaces have demonstrated only a spatially homogeneous polarization generation, while less attention has been devoted to spatially variant inhomogeneous vector beams. Here, a novel method for generating arbitrary radial and azimuthal polarization beams with high efficiencies of up to 80% is demonstrated by utilizing transmission‐type dielectric metasurfaces. Polarization conversion metasurfaces are suitable candidates for the implementation of polarization encryption, which is demonstrated by encoding a hidden image into the spatial polarization distribution. In addition, it is shown that the image pattern can be modified by appropriate polarization selection of the transmitted light. Such a method may provide a practical technique for a variety of applications such as imaging, encryption, and anticounterfeiting.

Demonstration of a terahertz pure vector beam by tailoring geometric phase

We demonstrate the creation of a vector beam by tailoring geometric phase of left- and right- circularly polarized beams. Such a vector beam with a uniform phase has not been demonstrated before because a vortex phase remains in the beam. We focus on vortex phase cancellation to generate vector beams in terahertz regions, and measure the geometric phase of the beam and its spatial distribution of polarization. We conduct proof-of-principle experiments for producing a vector beam with radial polarization and uniform phase at 0.36 THz. We determine the vortex phase of the vector beam to be below 4%, thus highlighting the extendibility and availability of the proposed concept to the super broadband spectral region from ultraviolet to terahertz. The extended range of our proposed techniques could lead to breakthroughs in the fields of microscopy, chiral nano-materials, and quantum information science.

Spatial variation of dynamic nuclear spin polarization probed by the non-local Hanle effect

The spatial distribution of dynamic nuclear spin polarization (DNP) has been investigated in a lateral all-semiconductor spin-injection device based on a (Ga,Mn)As/n+-GaAs spin-Esaki diode. The DNP induced by the hyperfine interaction has been probed via satellite peaks in non-local Hanle-type spin precession signals, indicating the recovery of electron spin polarization. A quantitative analysis using the self-consistent calculation reproduces the magnetic field position of the satellite peaks as a function of spin injection bias and injector-detector separation. The distance dependence of the Hanle curves reveals that the spin-lattice relaxation rather than the hyperfine interaction is the dominant mechanism of nuclear spin relaxation in the non-local region.

Control of polarization rotation in nonlinear propagation of fully structured light

Knowing, and controlling, the spatial polarization distribution of a beam is of importance in applications such as optical tweezing, imaging, material processing and communications. Here we show how the polarization distribution is affected by both linear and nonlinear (self-focussing) propagation. We derive an analytical ex- pression for the polarization rotation of fully-structured light (FSL) beams during linear propagation and show that the observed rotation is due entirely to the difference in Gouy phase between the two eigenmodes comprising the FSL beams, in excellent agreement with numerical simulations. We also explore the effect of cross-phase modulation due to self-focusing (Kerr) nonlinearity and show that polarization rotation can be controlled by changing the eigenmodes of the superposition, and physical parameters such as the beam size, the amount of Kerr nonlinearity and the input power. Finally, we show that by biasing cylindrical vector (CV) beams to have elliptical polarization, we can vary the polarization state from radial through spiral to azimuthal using nonlinear propagation.