Radial Polarization Research Articles

Total Internal Reflection Tip-Enhanced Raman Spectroscopy of Tau Fibrils.

Total internal reflection tip-enhanced Raman spectroscopy (TIR-TERS) has recently emerged as a promising technique for noninvasive nanoscale chemical characterization of biomolecules. We demonstrate that the TERS enhancement achieved in this experimental configuration is nearly 30 times higher than that in linear polarization and 8 times higher than that in radial polarization using traditional bottom-illumination geometry. TIR-TERS is applied to the study of Tau amyloid fibrils formed with the human full-length Tau protein mixed with heparin. This technique reveals the possibility to perform TERS imaging with 1-4 nm axial and 5-10 nm lateral spatial optical resolution. In these Tau/heparin fibrils, spectral signatures assigned to aromatic amino acid residues (phenylalanine, histidine, and tyrosine) and nonaromatic ones (e.g., cysteine, lysine, arginine, asparagine, and glutamine) are distinctly observed. Amide I and amide III bands can also be detected. In a fibril portion, it is shown that antiparallel β-sheets and fibril core β-sheets are abundant and are often localized in amino acid-rich regions where parallel β-sheets and random coils are present in lower proportions. This first TIR-TERS study on a nonresonant biological sample paves the way for future nanoscale chemical and structural characterization of biomolecules using this performant and original technique.

Stimulated Raman adiabatic passage in a quantum system near a plasmonic nanoparticle

We investigate theoretically the population transfer process in a Λ-type three-level quantum system (QS) near a metallic nanosphere using the stimulated Raman adiabatic passage (STIRAP) technique. We combine density matrix quantum dynamical calculations with first-principle electromagnetic calculations, which quantify the influence of the plasmonic nanoparticle on the electric field of the pump and Stokes pulses in STIRAP as well as on the spontaneous emission rates within the Λ-type system. We study the population transfer process by varying the free-space spontaneous emission rate, the distance of the QS from the nanosphere, the polarization direction with respect to the nanoparticle surface and the relative strength of the pump and Stokes pulses used in STIRAP. We find that when the pump and Stokes fields have tangential and radial polarizations with respect to the nanosphere surface, the transfer efficiency is improved due to the increase of the decay rate of the excited state to the target state relatively to the decay to the initial state. The optimal population transfer is achieved for small interparticle distances, moderate free space spontaneous decay rate, large values of the pump Rabi frequency and small values of the Stokes Rabi frequency. When we exchange the polarization directions of the pump and Stokes fields we can still find a range of parameters where the population transfer remains efficient, but larger Stokes Rabi frequencies are necessary to overcome the increased decay rate from the excited state back to the initial state.

RNA Binding Protein Rbms1 Enables Neuronal Differentiation and Radial Migration during Neocortical Development by Binding and Stabilizing the RNA Message for Efr3a.

Various RNA-binding proteins (RBPs) are key components in RNA metabolism and contribute to several neurodevelopmental disorders. To date, only a few of such RBPs have been characterized for their roles in neocortex development. Here, we show that the RBP, Rbms1, is required for radial migration, polarization and differentiation of neuronal progenitors to neurons in the neocortex development. Rbms1 expression is highest in the early development in the developing cortex, with its expression gradually diminishing from embryonic day 13.5 (E13.5) to postnatal day 0 (P0). From in utero electroporation (IUE) experiments when Rbms1 levels are knocked down in neuronal progenitors, their transition from multipolar to bipolar state is delayed and this is accompanied by a delay in radial migration of these cells. Reduced Rbms1 levels in vivo also reduces differentiation as evidenced by a decrease in levels of several differentiation markers, meanwhile having no significant effects on proliferation and cell cycle rates of these cells. As an RNA binding protein, we profiled the RNA binders of Rbms1 by a cross-linked-RIP sequencing assay, followed by quantitative real-time polymerase chain reaction verification and showed that Rbms1 binds and stabilizes the mRNA for Efr3a, a signaling adapter protein. We also demonstrate that ectopic Efr3a can recover the cells from the migration defects due to loss of Rbms1, both in vivo and in vitro migration assays with cultured cells. These imply that one of the functions of Rbms1 involves the stabilization of Efr3a RNA message, required for migration and maturation of neuronal progenitors in radial migration in the developing neocortex.

Propagation properties of partially coherent radially and azimuthally polarized vortex beams in turbulent atmosphere

Analytical formulas for the average intensity of the partially coherent radially and azimuthally polarized vortex (PCRPV and PCAPV) beams propagating through the turbulent atmosphere are derived based on the extended Huygens-Fresnel principle. The effect of the different topological charge number m of PCRPV beam and PCAPV beam in turbulence on average intensity and degree of hollowness (DOH) has been studied in detail. It can be found that PCRPV beam and PCAPV beam in turbulence with the larger topological charge m can greatly keep dark hollow constructure on propagation. And we have studied the orientation angles of the polarization ellipse of the PCRPV and PCAPV beams with different m in atmospheric turbulence. The results show that the capacity to keep radial polarization decline with the increase of topological charge m. In addition, we combined the complex screen method and multi-phase screens method to simulate the propagation of PCRPV beam and PCAPV beam in atmospheric turbulence for verifying our theoretical results. It is shown that the simulated results are consistent with theoretical results. Our study could be important for free-space optical communications.

Creation of cylindrical vector beams through highly anisotropic scattering media with a single scalar transmission matrix calibration

Cylindrical vector (CV) beams have attracted increasing interest due to their particular properties and their applications in optical imaging, optical manipulation, and light–matter interactions. However, it is challenging to construct CV beams through highly anisotropic scattering media (HASM), such as thick biological tissue, posing a barrier to the applications of CV beams that involve HASM. Here, we present a scheme to construct CV beams beyond high scattering that only requires a single scalar transmission matrix (TM) calibration and manipulation of the spatial degrees of freedom of the scalar input field. Assisted by a radial polarization converter (S-waveplate) and a polarizer, the scheme enables one to obtain the correct incident wavefront for the creation of CV beams through HASM with only one single scalar TM calibration. Compared to the existing method, this user-friendly approach is fast and simple in terms of the optical implements and computations. Both radially and azimuthally polarized beams are experimentally constructed through a ZnO scattering layer to demonstrate the viability of the method. Arbitrarily generalized CV beams and arrays of CV beams are also created through the HASM to further prove the flexibility of the method. We believe this work may pave the way for applications of CV beams that involve a highly anisotropic scattering environment.

Haidinger’s brushes: Psychophysical analysis of an entoptic phenomenon

Entoptic phenomena are visual artifacts arising from the interaction of light with the specific anatomic structure of the human eye. While they are usually too subtle to actually enable additional visual abilities, their perception can provide indirect information on the physiological conditions of the visual system. Among the most famous ones, Haidinger’s brushes consist in the appearance of a yellowish bow tie perceived in the presence of linearly polarized white light and originate from the particular spatial distribution of dichroic carotenoid molecules forming a sort of embedded radial polarizer in the foveal region. In this work, we develop a compact and versatile optical setup for the psychophysical analysis of the perceptual threshold of such entoptic effect. The tests performed on a group of 113 healthy individuals under conditions of maximum contrast (blue light) reveal the capability to perceive an average polarization degree around 16%. The developed prototype outlines a new optical platform to train the users in the perception of the phenomenon and infer information on the polarization-degree sensitivity of the human visual system.

Terahertz Bessel and "perfect" vortex beams generated with a binary axicon and axicon with continuous relief

Comparative studies of characteristics of Bessel and "perfect" vortex beams with a topological charge 9, created using a binary silicon axicon and a "holographic" diamond axicon with continu-ous profile at a wavelength of 141 μm, are carried out. Beams with linear and radial polarization are investigated. An example of the use of a perfect radially polarized beam for the excitation of vortex plasmon-polaritons on a cylindrical conductor is given.

Spin of Protons in NICA and PTR Storage Rings as an Axion Antenna

A new approach to search for axions in the storage ring experiments, applicable at a short coherence time of the in-plane polarization as is the case for protons is discussed. The technique can readily be applied at any storage ring equipped with internal polarimeter for the radial polarization of the beam (COSY, NICA, PTR). A possibility of substantial broadening of the range of attainable axion masses in storage rings with the hybrid electric and magnetic bending is pointed out, the PTR proton storage ring being an example.

Efficient electron acceleration by using Hermite-cosh-Gaussian laser beam in vacuum

The electron acceleration in vacuum has been studied theoretically using a radially polarized (RP) Hermite-cosh-Gaussian (HChG) laser beam. Even if the laser’s power is low, the RP HChG laser beam is quite effective and responsible for producing high energy electron. Due to the beauty (earlier focus) of such a laser beam, it is significantly better suited to acquiring GeV order energy over short periods of time than other laser beams. The electron acceleration process is strongly influenced by two more adjustable parameters associated with this beam: decentered parameter (b) and Hermite order (s). Throughout this investigation, better trapping phenomena have been identified. The effects of changing the intensity parameter (), the beam waist width (), the decentered parameter (b), and the order of the Hermite function on electron energy gain have been investigated.

Photocurrent detection of radially polarized optical vortex with hot electrons in Au/GaN

We report a GaN based metal–semiconductor–metal (MSM) infrared photodetector enabled with azimuthally distributed sub-wavelength gratings fabricated on one of the working electrodes. Under illumination, hot electron transfer is introduced by the plasmonic resonance in the infrared waveband formed at the interface of Au/GaN. Without the help of using any external optical polarizers, the device is able to detect radial polarization vortices in the form of photocurrents with a prescribed response spectrum. The detector exhibits a 10%–90% rise and fall time of 0.9 ms under modulated light, much faster than that of conventional ultraviolet GaN MSM photodetectors based on the band edge absorption. This work provides a viable way to measure spatially variant polarization beams with a compact plasmonic photodetectors fabricated from wide bandgap semiconductors.

Topological Charge of Light Fields with a Polarization Singularity

We have studied diverse vector and hybrid light fields, including those with multiple polarization singularities, and have derived relationships for polarization singularity indices based on the familiar Berry formula, which is normally utilized to find the topological charge of a scalar vortex light field. The fields with pure polar-angle-dependent polarization in the beam cross-section are shown to feature either polarization singularity lines outgoing from the center or a single polarization singularity point at the beam center. The fields with pure radial-variable-dependent polarization are shown to have no polarization singularities and zero polarization index. The vector fields with both polar-angle- and radial-variable-dependent polarization are shown to have multiple polarization singularity points that are scattered across the cross-section. A vector field with higher-order radial polarization and a real parameter was also studied and was shown to feature either several polarization singularity lines outgoing from the center or a central singular point, depending on the parameter value. Notably, at different parameter values, the polarization singularity index of such a field can take half-integer, integer, or zero values.

Helicity Transfer in Strong Laser Fields via the Electron Anomalous Magnetic Moment.

Electron beam longitudinal polarization during the interaction with counterpropagating circularly polarized ultraintense laser pulses is investigated, while accounting for the anomalous magnetic moment of the electron. Although it is known that the helicity transfer from the laser photons to the electron beam is suppressed in linear and nonlinear Compton scattering processes, we show that the helicity transfer nevertheless can happen via an intermediate step of the electron radiative transverse polarization, phase matched with the driving field, followed up by spin rotation into the longitudinal direction as induced by the anomalous magnetic moment of the electron. With spin-resolved QED MonteCarlo simulations, we demonstrate the consequent helicity transfer from laser photons to the electron beam with a degree up to 10%, along with an electron radial polarization up to 65% after multiple photon emissions in a femtosecond timescale. This effect is detectable with currently achievable laser facilities, evidencing the role of the leading QED vertex correction to the electron anomalous magnetic moment in the polarization dynamics in ultrastrong laser fields.

The tight-focusing properties of radially polarized symmetrical power-exponent-phase vortex beam

In this paper, the radially polarized (RP) new kind of power-exponent-phase vortex (NPEPV) beam, with rotationally symmetrical phase structure, was introduced and the tightly focused properties of the RP NPEPV beam passing through a high numerical aperture objective lens were studied numerically. The results show that with the increase of topological charge l, there are multiple intensity points in the focal region, and the number is consistent with the topological charge. In addition, as the power order n increases, the light intensity gradually concentrates on the central optical axis and the surrounding intensity points gradually disappear, which finally presents a Gaussian intensity distribution with the dark cores gradually move away from the optical axis and disappear. These unique properties will have potential applications in particle trapping and laser fabrication, especially for simultaneous trapping of multiple particles and fabrication of chiral microstructures.

Multidimensional trapping by dual-focusing cylindrical vector beams with all-silicon metalens

Dual-focusing effect with a cylindrical vector-light characteristic (i.e., radial and azimuthal polarizations) is theoretically proposed and numerically demonstrated by spin-decoupled phase control with all-silicon metalens. Attributed to the polarization dependence, the pair of focusing cylindrical vector beams can be interchanged by orthogonally switching the polarization of incident light. We demonstrate the unique contributions of focused radial and azimuthal vector beams to longitudinal and transverse optical forces on glass spheres, respectively, by calculations based on the Maxwell stress tensor. This paper presents the use of all-silicon metalens with highly-compact vector beams, promising for applications such as multidimensional optical trapping.

High-resolution dark-field confocal microscopy based on radially polarized illumination.

Dark-field confocal microscopy (DFCM) facilitates the 3D detection and localization of surface and subsurface defects in high-precision optical components. The spatial resolution of conventional DFCM is commonly undermined owing to complementary aperture detection. We employed a radially polarized (RP) beam for illumination in DFCM. The RP beam creates a sub-diffraction-sized longitudinal optical component after being focused and effectively enhances the lateral resolution by 30.33% from 610 nm to 425 nm. The resolution improvement was verified by imaging a 2D sample containing sparsely distributed gold nanorods along with a 3D neodymium glass containing surface and subsurface defects.

Detecting cylindrical vector beams with an on-chip plasmonic spin-Hall metalens

In recent years, singular optical beams, including optical vortex (OV) beams with phase singularities and cylindrical vector beams (CVBs) with polarization singularities, have brought new degrees of freedom for many applications. Although there have been various microscale devices for OV detection, the detection of CVBs with a microscale device is still a challenge. Here, we propose a new method for detection of CVBs with a designed on-chip plasmonic spin-Hall metalens structure. The focal position of the metalens and the splitting effect of at focus are studied in both an analytical model and numerical simulation. The results demonstrate that the metalens can not only detect different polarization orders of incident CVBs but also have an ability to distinguish radial, azimuthal and other vectorial polarization states under the same order of CVBs. This method has potential applications in compact integrated optical communication and processing systems.

Coherent generation of arbitrary first-order Poincaré sphere beams on an Si chip.

Generalized vector vortex light beams possess spatially variant polarization states, and higher-order Poincaré spheres represent a powerful analytical tool for analyzing these intriguing and complicated optical fields. For the generation of these vortex beams, a range of different methods have been explored, with an increasing emphasis placed on compact, integrated devices. Here, we demonstrate via numerical simulation, for the first time, an on-chip light emitter that allows for the controllable generation of all points on a first-order Poincaré sphere (FOPS). The FOPS beam generator consists of a waveguide-coupled, nanostructured Si microring resonator that converts two guided, coherent light waves into freely propagating output light. By matching their whispering gallery modes with the nanostructures, the fundamental TE (transverse electric) and TM (transverse magnetic) input modes produce radial and azimuthal polarizations, respectively. These two linear polarizations can form a pair of eigenstates for the FOPS. Consequently, tuning the phase contrast and the intensity ratio of these two coherent inputs allows for the generation of an arbitrary point on the FOPS. This result indicates a new way for on-chip vector vortex beam generation, which may be applied for integrated optical tweezers and high-capacity optical communications.

FASN-dependent de novo lipogenesis is required for brain development

Fate and behavior of neural progenitor cells are tightly regulated during mammalian brain development. Metabolic pathways, such as glycolysis and oxidative phosphorylation, that are required for supplying energy and providing molecular building blocks to generate cells govern progenitor function. However, the role of de novo lipogenesis, which is the conversion of glucose into fatty acids through the multienzyme protein fatty acid synthase (FASN), for brain development remains unknown. Using Emx1Cre-mediated, tissue-specific deletion of Fasn in the mouse embryonic telencephalon, we show that loss of FASN causes severe microcephaly, largely due to altered polarity of apical, radial glia progenitors and reduced progenitor proliferation. Furthermore, genetic deletion and pharmacological inhibition of FASN in human embryonic stem cell-derived forebrain organoids identifies a conserved role of FASN-dependent lipogenesis for radial glia cell polarity in human brain organoids. Thus, our data establish a role of de novo lipogenesis for mouse and human brain development and identify a link between progenitor-cell polarity and lipid metabolism.

Lateral shifts of linearly- and radially-polarized Bessel beams scattered by a nanosphere.

We report the investigation on the lateral shifts that linearly-polarized (LP) and radially-polarized (RP) Bessel beams experience during the Mie scattering by a nanosphere. A numerical procedure based on the angular spectrum theory is developed to solve the scattered electromagnetic field and subsequent lateral shifts with a high computational efficiency, which can be easily applied to an arbitrary shaped polarized beam. The influences of different factors, including conical angle, nanosphere radius and position, on the lateral shifts are systematically investigated. The results demonstrate that for on-axis scattering, a LP Bessel beam can be regarded as a plane wave with the same polarization state but an equivalent longer wavelength, while a RP Bessel beam can be regarded as a plane wave with a polarization state along the propagation direction exhibiting independence on the conical angle. The findings help deepen our understandings of lateral shifts in light scattering of vectorial non-diffractive beams.

Stokes CMOS polarimetry limits studied at non-classical polarisation states

We present the study of the two polarisation state analysers. The first consists of a polarisation camera with a removable QWP, and the second consists of a non-polarisation camera with a rotating QWP and a stationary linear polariser. The theoretical analysis and experiment focus on studying the influence of polarimeter optical components accuracy and errors such as retardation errors, misalignments and extinction ratio on Stokes parameters precision. This research is a cornerstone to understanding polarisation state analysers limits. We examined laser beams with non-classical polarisation distribution, namely the Poincaré beam and the beam with radial polarisation.