Polarization Vector Of Light Research Articles

Switchable anisotropic diffraction mode filter based on fork-like liquid crystal gratings

The interaction of liquid crystal (LC) fork-like gratings (FLGs) with a Laguerre–Gaussian beam of the TEM00 mode is described. It is experimentally shown that when the direction of the light polarization vector differs from the direction of the LC eigenvectors, the medium behaves as an FLG with a controlled modulation depth, and in the opposite case, it is isotropic and homogeneous. Distributions of the intensities of the longitudinal section of the beam in the infinitely far field are given depending on the FLG rotation angle in the plane perpendicular to the direction of beam propagation. It is shown that the LC FLG functions as a switchable anisotropic diffraction mode filter.

The Twisting of Radio Waves in a Randomly Inhomogeneous Plasma

Polarization of electromagnetic waves carries a large amount of information about their astrophysical emitters and the media they passed through, and hence is crucial in various aspects of astronomy. Here we demonstrate an important but long-overlooked depolarization mechanism in astrophysics: when the polarization vector of light travels along a nonplanar curve, it experiences an additional rotation, in particular for radio waves. The process leads to depolarization, which we call “geometric” depolarization (GDP). We give a concise theoretical analysis of the GDP effect on the transport of radio waves in a randomly inhomogeneous plasma under the geometrical optics approximation. In the case of isotropic scattering in the coronal plasma, we show that the GDP of the angle of arrival of the linearly polarized radio waves propagating through the turbulent plasma cannot be ignored. The GDP effect of linearly polarized radio waves can be generalized to astrophysical phenomena, such as fast radio bursts and stellar radio bursts, etc. Our findings may have a profound impact on the analysis of astrophysical depolarization phenomena.

Double Hanle resonance dependence on light polarization angle and transverse magnetic field direction

We present experimental and theoretical investigations of the dependence of double Hanle resonance spectrum on the light polarization angle and the direction of the applied transverse magnetic field (TMF). The experiments are done for Fg=2→Fe=1 transition of 87Rb D1 line using a rubidium vapor cell containing buffer gas. We show that a small light polarization component along the direction of TMF introduces asymmetry in the double Hanle resonance signal. Both the magnitude and sign of asymmetry in the signal are sensitive to the TMF orientation, suggesting a possible method for in-situ measurement of the direction of the magnetic fields generated by the coils. The physical origin of this asymmetry is explained by considering the redistribution of population among the ground-state Zeeman sublevels in the presence of TMF. In addition, we systematically vary both the polarization angle and TMF direction to study their effect on the line profile of Hanle resonances. We demonstrate that a double Hanle resonance changes to a dark Hanle resonance by rotating the light polarization vector irrespective of the TMF direction. We have developed a simple theoretical model based on a degenerate two-level system to explain our experimental observations.

Geometric phase for twisted light.

Polarization vectors of light traveling in a coiled optical fiber rotate around its propagating axis even in the absence of birefringence. This rotation was usually explained due to the Pancharatnam-Berry phase of spin-1 photons. Here, we use a purely geometric method to understand this rotation. We show that similar geometric rotations also exist for twisted light carrying orbital angular momentum (OAM). The corresponding geometric phase can be applied in photonic OAM-state-based quantum computation and quantum sensing.

Electronic structure and terahertz intersubband absorption spectra of phosphorus donor in silicon using a variationally optimized diagonalization method

The electronic structure and terahertz (THz) intersubband absorption spectra of phosphorus (P) donor in silicon (Si) are theoretically investigated using a variationally optimized diagonalization method based on the three-dimensional (3D) nonorthogonal associated Laguerre basis set, the basis set of eigenfunctions of 3D hydrogen atom and the basis set of eigenfunctions of 3D isotropic harmonic oscillator. A fully analytical expression of the matrix elements of the Hamiltonian is derived. Due to the large band anisotropy of Si, the donor electron series appear in an anomalous energy-level order and interval of the orbital angular momentum. The donor electron energy levels with even a small number of basis functions are in excellent agreement with those reported in the previous literature. Compared to two different basis sets of eigenfunctions of 3D hydrogen atom and isotropic harmonic oscillator, my proposed variationally optimized diagonalization method based on the 3D nonorthogonal associated Laguerre basis set is proven to be more efficient and reliable in calculating highly accurate impurity states of anisotropic 3D materials. The intersubband absorption spectra of P donor electron involving transitions from the 1s to excited states are strongly dependent on the orientations of the valley and the polarization vector of the incident light, which results from the fact that the large band anisotropy of Si induces strong mixing of the donor electron states. Their absorption frequencies are found to fall into the THz part of the electromagnetic spectrum. These results show that P donor in Si provides a material platform that enables intersubband devices operating in the THz frequency domain. • A fully analytical expression of the matrix elements of the donor Hamiltonian is derived. • The donor electron energy levels are in excellent agreement with those reported in the previous literature. • The intersubband absorption spectra of P donor electron are strongly dependent on the orientations of the incident light polarization. • P donor in Si provides a material platform that enables optoelectronic devices operating in the THz frequency domain. • The 3D nonorthogonal Laguerre basis is more efficient and reliable in calculating impurity states of anisotropic 3D materials.

Linear and nonlinear optical properties in single CuIn1−xGaxSe2 nanowire: Effects of size, incident intensity, relaxation time and Ga concentration

The linear and nonlinear optical properties of CuIn1−xGaxSe2 free standing nanowire have been studied by employing the compact-density matrix formalism and the effective mass approximation. Considering the system under the effect of the polarization vector of the incident light in both cases perpendicular and parallel to the axis of the nanowire, the systematic theoretical investigation contains results with all possible combinations of the involved parameters, such as incident light intensity, relaxation time, nanowire radius and Ga concentration. Our results show that in the case of the polarization vector perpendicular to the nanowire axis, the linear and nonlinear absorption coefficient and refractive index changes can be controlled by changing the nanowire radius, and the effect of Ga concentration is clearly apparent. In contrast, polarization along the nanowire axis allows for a very large absorption coefficient and control of the optical properties through the height, but minimal effect on the transition energy. The increase of the relaxation time as well as the intensity of the incident light has a major role in the nonlinearity effects, while the Ga concentration and the size of the structure influence the amplitude and the transition energy shift.

Selection rule for the photoinduced phase transition dominated by anisotropy of strain in Ti3O5

In photoinduced phase transitions, the relationship between the crystal orientation and the direction of the polarization or wave vector of light seems important, but surprisingly, such directional properties in photoinduced phase transitions have not been well studied experimentally. ${\mathrm{Ti}}_{3}{\mathrm{O}}_{5}$ exhibits a structural phase transition involving the anisotropic migration of Ti and O ions, and its nanocrystals exhibit a persistent photoinduced phase transition. We found that a photoinduced phase transition occurs even in a single crystal of this compound, but it significantly depends on the orientation of the plane on which the light is irradiated. Such a selection rule for photoinduced phase transitions is dominated by the anisotropy of the strain associated with the phase transition.

Selective trapping of chiral nanoparticles via vector Lissajous beams.

We report selective trapping of chiral nanoparticles via vector Lissajous beams. Local optical chirality densities appear in these beams by properly choosing the values of two parameters (p,q) that determine the polarization vectors of light. For a particular set of parameter (p,q) = (2,1) which is found preferable for the selective trapping, the resulting vector beam has two dominant intensity spots with opposite chirality. In the transverse plane, one spot traps a chiral particle while the other one repels the same particle under appropriate conditions, which can be reversed for a particle of opposite chirality. Various chiral parameters and radii of a particle are considered for analyzing this selective trapping effect. The longitudinal forces that are found non-conservative are also discussed. The achieved functionality of identifying and separating different chiral particles may find applications in enantiomer separation and drug delivery in pharmaceutics.

Orbital selective dynamics in Fe-pnictides triggered by polarized pump pulse excitations

Quantum materials display exotic behaviours related to the interplay between temperature-driven phase transitions. Here, we study the electron dynamics in one such material, CaFe2As2, a parent Fe-based superconductor, employing time- and angle-resolved photoemission spectroscopy. CaFe2As2 exhibits concomitant transition to spin density wave state and tetragonal to orthorhombic structure below 170 K. The Fermi surface of this material consists of three hole pockets , β and around the Γ-point and two electron pockets around the X-point. The hole pockets have d xy , d yz and d zx orbital symmetries. The β band constituted by d xz /d yz orbitals exhibits a gap across the magnetic phase transition. We discover that polarized pump pulses can induce excitations of electrons of a selected symmetry. More specifically, while s-polarized light (polarization vector perpendicular to the xz plane) excites electrons corresponding to all the three hole bands, p-polarized light excites electrons essentially from , bands which are responsible for magnetic order. Interestingly, within the magnetically ordered phase, the excitation due to the p-polarized pump pulses occur at a time scale of 50 fs, which is significantly faster than the excitation induced by s-polarized light (∼200 fs). These results suggest that the relaxation of different ordered phases occurs at different time scales and this method can be used to achieve selective excitations to disentangle complexity in the study of quantum materials.

Production of dichromatic light with a rotating polarization vector using a single Bragg cell

We propose an approach for producing a rotating polarization vector of dichromatic light controlled by the acoustic frequency. This approach is based on diffraction of one of the eigenmodes for each monochromatic component during two passes of dichromatic light through a gyrotropic acousto-optical cell and is demonstrated using rotation in the polarization of dichromatic light generated by an Ar laser at wavelengths of 0.488 µm and 0.514 µm using a paratellurite acousto-optical cell operating at 108 MHz.

Effects of geometric optics in conformal Weyl gravity

We have investigated effect of geometric optics as the rotation of polarization vector of light in spacetime of gravitational compact object in the fourth-order theory of conformal Weyl gravity. The Pineault–Roeder method is applied to the rotating Weyl metric, and analytical results are obtained in the limit of weak field and or slow rotation. For the photon traveling parallel to the symmetry axes from the equatorial plane to infinity, the rotation of the polarization plane depends on the Weyl parameter gamma on the contrary to the Kerr spacetime where there is no rotation of polarization plane for this case.

Raman spectroscopy regulation in van der Waals crystals

Raman spectroscopy is a versatile tool widely used for comprehensive probing of crystal information. However, generally when applied in narrow-band-gap van der Waals crystals, it is liable to form a “bug,” especially in transition-metal-dichalcogenides (TMDs). That is, several resonant Raman-scattering (RS) modes will inevitably appear in the Raman spectra with strong intensity, interfering with the desired signal of optical-phonon modes. Here, we propose cross-sectional polarized Raman scattering capable of regulating the intensity of RS modes in accordance with quasi-sinusoidal rules. Typically, for MoS2 and WS2, when the polarization vector of excited light is along the c axis of the crystal, all RS modes are nearly completely “expunged” from the Raman spectra. The mechanism is that the absorption of most TMDs with a space group of R3m for the light polarized along the c axis is infinitesimal, thus forming a small coupling intensity of electronic states excited optically and acoustic-phonon modes at point M, which in turn restrain the appearance of RS modes. The regulating strategy proposed can be applied to other van der Waals crystals so as to obtain a high signal-to-noise ratio Raman spectrum.

Theoretical study on the nondipole asymmetries of Kr 1s1/2 and 4p3/2 photoelectrons

A theoretical study has been conducted on nondipole asymmetry parameters and angular distribution of Kr 1s1/2 and 4p3/2 photoelectrons with Dirac-Fock method based on the density matrix theory, with a focus on the impacts of nondipoles on the photoelectron angular distribution. The results show that the electric-dipole–electric-quadrupole E1 and E2 interference has a significant influence on the spatial angular distribution of Kr 1s1/2 and 4p3/2 photoelectrons. To be specific, the photoelectron characteristics relevant to the direction of the polarization vector of the incident light can be destroyed by the E1 and E2 interference. For the Kr 4p3/2 photoelectron, it is suggested that the non-dipole effects of photoelectron distribution be measured in two energy positions where the electric dipole β parameter equals to zero. Higher order nondipole effects are negligible according to the investigations. Our calculations consist well with the available experimental and theoretical results.

Template-Free Synthesis of Periodic Three-Dimensional PbSe Nanostructures via Photoelectrodeposition.

Highly periodic, geometrically directed, anisotropic Se-Pb films have been synthesized at room temperature from an isotropic aqueous solution without the use of physical templates by photoelectrodeposition using a series of discrete input illumination polarizations and wavelengths from an unstructured, uncorrelated, incoherent light source. Dark growth did not generate deposits with substantial long-range order, but growth using unpolarized illumination resulted in an ordered, nanoscale, mesh-type morphology. Linearly polarized illumination generated Se-Pb deposits that displayed an ordered, highly anisotropic lamellar pattern wherein the long axes of the lamellae were aligned parallel to the light polarization vector. The pitch of the lamellar features was proportional to the input light wavelength, as confirmed by Fourier analysis. Full-wave electromagnetic and Monte Carlo growth simulations that incorporated only the fundamental light-matter interactions during growth successfully reproduced the experimentally observed morphologies and quantitatively matched the pattern periodicities. Electrochemical postprocessing of the as-deposited Se-Pb structures resulted in the generation of stoichiometric, crystalline PbSe while preserving the nanopatterned morphology, thus broadening the genus of materials that can be prepared with controlled three-dimensional morphologies through maskless photoelectrodeposition.

Curvature effect on polarization of light emitted from chiral carbon nanotubes.

We investigate that effect of the curvature on induced hybridization and modification of emission profiles for each chiral's index single-wall carbon nanotubes (SWCNTs). According to the Schwinger two particle pair state method, we provide an analytical expression by calculating polar of spot intensity as a function of the polar angle. The emission profiles for indirect transition have an asymmetric shape as a function of the electron wave vector of the axis direction kt and depend on the chiral index. Here we show polarization-dependent, given analytically by expanding the matrix element into the scalar product of the light polarization vector and the dipole vector. These scalar products having a maximum value depend on the summation of phase factors of spinors of electrons in the conduction band Φc and valence band Φv. In the case of direct transition, dipole vector tube axis is maximum at the phase summation of Φc and Φv is 0 or 2π. In contrast, the maximum dipole vector circumference is obtained at the phase summation of π for the case of indirect transition. We can predict a strong emission peak and emission profiles which can be used to identify optical transitions in an individual SWCNT with different chiral indices experimentally.

Determination of Crystal Axes in Semimetallic T′‐MoTe2 by Polarized Raman Spectroscopy

Distorted octahedral T′ phase of MoTe2 has recently attracted significant interest due to its predicted topological states and novel charge transport properties. Here, we report a nondestructive method for determining the crystal orientation of few‐layer T′‐MoTe2 flakes by polarized Raman spectroscopy. The experimentally observed Raman modes are assigned to eigenmodes of vibrations predicted by density functional theory calculations. Polarized Raman measurements reveal four distinct types of angle‐dependent intensity variations. From group theory, it can be deduced that the intensity of the Bg mode reaches a maximum in the configuration when the polarization vector of the incident light is either parallel or orthogonal to the metal–metal zigzag chain direction. The intensity variation of the Bg mode cannot be used to unambiguously determine the crystal orientation. Using electron diffraction analysis, it is demonstrated that the intensity of the Ag mode at around 162 cm−1 reaches a maximum when the polarization vector of the incident light is parallel to the metal–metal chain direction in the configuration. Furthermore, a simple method is proposed for identifying crystal orientation in nonpolarized Raman spectroscopy.

Non-dipole effects in the angular distributions of photoelectrons on sodium-like ions

Photoionization processes widely exist in the astrophysical plasma and the high temperature laboratory plasma. Compared with the traditional photoelectron energy spectrum, the photoelectron angular distribution is not only related to the amplitude of the photoionization channels, but also sensitive to the phases of these channels. So the photoelectron angular distribution contains much more quantum information about the photoionization processes and is used to provide stringent tests of our understanding of basic physical processes underlying gas- and condensed-phase interaction with radiation, as well as a tool to probe physical and chemical structure in solids and surfaces. For a long time, the dipole approximation has been the basis in the study of the photoelectron angular distribution, but with the progress of light source, such as the fourth generation synchrotron facilities, more and more attention is paid to the non-dipole effect of the photoelectron angular distribution. In thispresent work, the photoionization processes of sodium-like ions (20Z92) are studied for the different incident photon energies based on the multiconfiguration Dirac-Fock method and the density matrix theory. The influences of the non-dipole terms on the photoelectron angular distributions, which arise from the multipole expansion of the electron-photon interaction, are discussed in detail. The relationship between the dipole and non-dipole parameters of the photoelectron angular distribution along with the atomic number is given. It is found that the influence of non-dipole terms on the photoelectron angular distribution is related to the incident photon energy and the atomic number of the target ion and the subshell of the ionized electron. In general, the influences of the non-dipole terms on the photoelectron angular distribution of p subshell are larger than those of the s subshell. In the electric dipole approximation, the s subshell photoelectron angular distribution is nearly independent of the photon energy and nuclear charge number, but this situation is not for the p subshell. With the increase of photon energy, an abnormal angular distribution is found for the p subshell photoelectron. However, if the non-dipole effects are included, the abnormal photoelectron angular distribution of p subshell disappears and the photoelectron distribution has maximum values respectively near 45o and 135o with respect to the polarization vector of incident light, that is, the photoelectron distribution has an obvious forward scattering characteristic.

A dead-zone free ⁴He atomic magnetometer with intensity-modulated linearly polarized light and a liquid crystal polarization rotator.

We demonstrate an all-optical (4)He atomic magnetometer experimental scheme based on an original Bell-Bloom configuration. A single intensity-modulated linearly polarized laser beam is used both for generating spin polarization within a single (4)He vapor and probing the spin precessing under a static magnetic field. The transmitted light signal from the vapor is then phase-sensitively detected at the modulation frequency and its harmonics, which lead to the atomic magnetic resonance signals. Based on this structure, a liquid crystal is added in our magnetometer system and constitutes a polarization rotator. By controlling the voltage applied on the liquid crystal, the light linear polarization vector can be kept perpendicular with the ambient magnetic field direction, which in turn provides the maximum resonance signal amplitude. Moreover, the system exhibits a magnetic-field noise floor of about 2pT/√Hz, which is not degraded due to the presence of the liquid crystal and varying magnetic field direction. The experiment results prove that our method can eliminate the dead-zone effect, improve the system spatial isotropy, and thus be suitable in mobile applications.

Simulation of molecular imaging using nanowire optical probe with flat end face

In this paper, the output near field of nanowire with flat end face is calculated, and the nanowire as light-emitting probe for near-field imaging of 30nm diameter spherical gold nanoparticles representing biomarkers for labeling biological cells or molecules is simulated by using the three-dimensional finite-difference time-domain (3D FDTD) method. Due to the near-field enhancement effect at the edge of the nanowire and the local surface plasmon enhancement effect of gold nanoparticles induced by the output near field of the nanowire, the near field at the nanoparticles has the strongest peak when the x–y positions of the nanoparticles are close to the perimeter of the nanowire. Simulation results also show that the near field at the gold nanoparticles highly depends on the polarization vector of the incident light and the nanowire can work effectively as optical probe for molecular imaging. Results presented here can offer valuable references for molecular imaging technology with nanowires as optical probes.

Accurate treatment of total photoabsorption cross sections by an ab initio time-dependent method

A detailed discussion of parallel and perpendicular transitions required for the photoabsorption of a molecule is presented within a time-dependent view. Total photoabsorption cross sections for the first two ultraviolet absorption bands of the N2O molecule corresponding to transitions from the X1 A′ state to the 21 A′ and 11 A′′ states are calculated to test the reliability of the method. By fully considering the property of the electric field polarization vector of the incident light, the method treats the coupling of angular momentum and the parity differently for two kinds of transitions depending on the direction of the vector whether it is: (a) situated parallel in a molecular plane for an electronic transition between states with the same symmetry; (b) situated perpendicular to a molecular plane for an electronic transition between states with different symmetry. Through this, for those transitions, we are able to offer an insightful picture of the dynamics involved and to characterize some new aspects in the photoabsorption process of N2O. Our calculations predicted that the parallel transition to the 21 A′ state is the major dissociation pathway which is in qualitative agreement with the experimental observations. Most importantly, a significant improvement in the absolute value of the total cross section over previous theoretical results [R. Schinke, J. Chem. Phys. 134, 064313 (2011), M.N. Daud, G.G. Balint-Kurti, A. Brown, J. Chem. Phys. 122, 054305 (2005), S. Nanbu, M.S. Johnson, J. Phys. Chem. A 108, 8905 (2004)] was obtained.