Elliptically Polarized Research Articles

Elliptical polarization of the magnetic field of parallel currents and methods of their determination

Determination of positions and electrical currents of underground pipelines using the electro¬magnetic method allows us to draw conclusions about the quality of the insulation of pipelines. The analysis of the spatial characteristics of the magnetic field of the low-frequency current of the pipeline is carried out on the basis of the Biot-Savard-Laplace law, which determines the dependence of the components of the magnetic field on the given current in a homogeneous, boundless space. It is shown that for two or more parallel pipelines to each other placed close, it is necessary to take into account their total magnetic field. A mathematical model of the magnetic field of parallel rectilinear alternating electric currents was developed, taking into account the phase difference between them, which leads to the emergence of an elliptically polarized total magnetic field. The methods of determining the coordinates of the currents of parallel underground pipelines are analyzed. The relation of the components of the magnetic field for different coordinates of the pipelines, currents and the phase difference between the currents was obtained. Known methods of determining the coor¬dinates and currents of parallel underground pipelines are intended for the partial case of linear polarization of the magnetic field (with in-phase or anti-phase currents). In the general case of elliptic polarization of the magnetic field, a combination of tuning and scanning methods should be used.

3D digital holographic polarimetry of diffuse optically anisotropic biological tissue object fields

The experimental validation of methods for the digital holographic 3D layer-by-layer reconstruction of complex amplitude distributions in different phase planes of diffuse biological tissue histological section microscopic images with a subsequent reconstruction of azimuth and ellipticity polarization maps is presented. Polarization dependencies of the integral and layer-by-layer vector structure of the laser object field azimuth and ellipticity distributions in two types of biological layer samples—the fibrous myocardium and parenchymal liver—have been investigated. Scenarios and dynamics of changes in the values of statistical moments of the first to fourth orders, which characterize the integral and layer-by-layer polarization maps of diffuse biological tissue histological section microscopic images with different morphological structures, have been determined. Criteria for selecting the polarization components of the object field that are formed by acts of scattering of different multiplicities have been identified. An example of biomedical application in cancer detection of biological tissues is provided.

Spin angular momentum at the sharp focus of a cylindrical vector vortex beam

Sharp focusing of a light field with double (phase and polarization) singularity is studied. Using the Richards-Wolf method, an exact analytical expression for the longitudinal projection of the spin angular momentum (SAM) vector at the focus is obtained. The expression derived suggests that 4 (n –1) subwavelength regions are formed at the focus, where n is the cylindrical vector beam order, with their centers located on a certain circle centered on the optical axis. Notably, the SAM projections are found to have the opposite sign in the neighboring regions. This means that in the neighboring focal regions, the light has alternating left or right elliptical polarization (manifestation of a spin Hall effect). At the center of the focal spot near the optical axis, the field is right-handed elliptically polarized at m > 0, or left-handed elliptically polarized at m < 0, where m is the vortex charge. The total longitudinal spin, i.e., the longitudinal SAM component averaged over the beam-cross section, is zero and preserved upon focusing. Due to the beam containing an optical vortex with charge m, the transverse energy flow rotates on a spiral path near the focal plane, rotating on a circle in the focal plane. The rotation direction near the optical axis is counterclockwise for m > 0, and clockwise for m < 0.

Terahertz metasurface polarization detection employing vortex pattern recognition

The manipulation and detection of polarization states play a crucial role in the application of 6G terahertz communication. Nonetheless, the development of compact and versatile polarization detection devices capable of detecting arbitrary polarizations continues to be a challenging endeavor. Here, we demonstrate a terahertz polarization detection scheme by performing mode purity analysis and multidimensional analysis of the transmitted vortex field. The power of the proposed polarization recognition is verified by using three polarization trajectories, including linear polarizations, circular polarizations, and elliptical polarizations. Using the reconstructed complete polarization parameters, the detected polarization states are characterized using polarization ellipses, Poincaré sphere, and full-Stokes parameters. The experimental results validate the power of this scheme in polarization detection. This scheme holds promise for applications in polarization imaging and terahertz communication.

A planar cloverleaf antenna for circularly polarized microwave fields in atomic and molecular physics experiments

We report on the design and characterization of a compact microwave antenna for atomic and molecular physics experiments. The antenna is comprised of four loop antennas arranged in a cloverleaf shape, allowing for precise adjustment of polarization by tuning the relative phase of the loops. We optimize the antenna for left-circularly polarized microwaves at 3.5 GHz and characterize its near-field performance using ultracold NaCs molecules as a precise quantum sensor. Observing an unusually high Rabi frequency of 2π × 46.1(2) MHz, we extract an electric field amplitude of 33(2) V/cm at 22 mm distance from the antenna. The polarization ellipticity is 2.3(4)°, corresponding to a 24 dB suppression of right-circular polarization. The cloverleaf antenna is planar and provides large optical access, making it highly suitable for quantum control of atoms and molecules and potentially other quantum systems that operate in the microwave regime.

Elliptically polarized, nanosecond dual-pulse Raman laser with tunable pulse interval and pulse amplitude ratio

Dual-pulse solid state lasers with pulse interval of tens nanoseconds have been applied in laser-induced breakdown spectroscopy, laser drilling, medical treatment, and atmospheric monitoring. Here, a Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman laser has been developed for generating dual-pulse lasers with tunable pulse interval and elliptical polarization. Pulse interval and pulse amplitude ratio between peaks of satellite pulse and main pulse are controlled by adjusting the incident pump power (Pin). As Pin increases from 1.3 to 5.9 W, the pulse interval decreases from 63.1 to 36.3 ns, and the pulse amplitude ratio between peaks of satellite pulse and main pulse increases from 0.1 to 1.1 for dual-pulse Raman lasers. At Pin = 4.9 W, dual-pulse Raman laser with equal peak power of 1.7 kW and pulse interval of 40.2 ns is obtained. The pulse widths are 2.7 and 3.6 ns, and the pulse energy are 4.6 and 6.2 μJ for the main pulse and satellite pulse, respectively. The elliptical polarization with ellipticity tunable from 0.08 to 0.54 is obtained for dual-pulse passively Q-switched Raman laser as Pin increases. Such a nanosecond dual-pulse laser source has the potential to expand simple, compact portable and economical laser applications in various fields.

Polarization helicity and the optical spin-orbit Hall effect

The optical spin-orbit Hall effect manifests the separation of the spin angular momentum (SAM) and the orbital angular momentum (OAM), yet it can be obtained for the radially polarized light and well controlled by the initial phase of the polarization state which leads to the twist of its distribution. In this paper, we introduce the polarization helicity to characterize the effect of the initial phase of the polarization states in the optical spin-orbit Hall effect. We find the polarization helicity of the radial polarization state can be modulated by changing its initial phase, and the polarization helicity of the high-order polarization state always is zero. We show that the separation magnitude of the SAM and the OAM reach the maximum value when the initial phase of the radial polarization state equals π/4 (or −π/4). The sign of the SAM and the OAM are determined by the polarization helicity of incident light and the anisotropy of uniaxial crystal, and its evolution follows a sinusoidal function. Furthermore, the polarization state of the incident radially polarized light will evolve into the left-handed (or right-handed) elliptical polarization state as the change of the polarization helicity of incident light. Our studies further deepen the understanding of the spin-orbit coupling of the vector beams, and provide a potential technique for modulating the polarization state of the light in uniaxial crystal.

Effect of light ellipticity and polarization angle on the transient dynamics of the ground-state Hanle effect

We report theoretical investigations on the transient dynamics of the ground-state Hanle effect in the Voigt geometry, where a time-varying scanning magnetic field B (t) is applied perpendicular to the light propagation direction. Transient Hanle signals are calculated for different light polarizations using a theoretical model based on the density matrix approach. First, we study the ellipticity dependence of transient Hanle signals in two configurations in which the major axis of the light polarization ellipse () is aligned either perpendicular or parallel to the field B . For B , elliptical polarization of the light produces oscillations of frequencies 2ΩL(t) and ΩL(t) simultaneously, where ΩL(t) is the Larmor frequency of the corresponding field B (t). On the other hand, in the case of || B , only ΩL(t) oscillation is observed using elliptically polarized light. Second, we vary the tilt angle between the polarization vector of a linearly polarized light and the orientation of the field B and study its effect on the transient response of Hanle signals. Both the amplitude and the decay rate of the oscillations show a strong dependence on the light ellipticity and tilt angle of the polarization vector. In addition, the influence of the magnetic field sweep rate on the transient signals is demonstrated for given values of light ellipticity and polarization angle.

All-dielectric six-foci metalens for infrared polarization detection based on Stokes space.

The detection technology of infrared polarization has gained significant attention due to its ability to provide better identification and obtain more information about the target. In this paper, based on the expression of the full polarization state in Stokes space, we designed micro-nano metasurface functional arrays to calculate the polarization state of the incident light by reading the Stokes parameters (a set of parameters that describe the polarization state). Metalens with linear and circular polarization-dependent functions are designed based on the propagation and geometric phases of the dielectric Si meta-atoms in the infrared band, respectively. The device exhibits a high polarization extinction ratio. The influence of incident angle on polarization-dependent metalens is discussed, and the analysis of incident angle is of great significance for the practical application. An infrared six-foci metalens is proposed, each corresponding to the Poincaré sphere's coordinate component (a graphical polarization state method). By matching the six polarization components of the incident light and the Stokes parameters, the polarization detection function can be realized by calculating the polarization state of the incident light. There is a slight error between the theoretical value and the calculated value of the unit coordinate component of the Stokes parameters. At the same time, the intensity distribution of different incident light polarization azimuth angles and ellipticity angles on the focal plane agrees with the theory. The advantage of the device is that the polarization state of the incident light can be directly calculated without passing through other components. The six-foci metalens have potential applications in polarization detection and imaging, space remote sensing, etc.

Generating Angular-Varying Time Delays of THz Pulses via Direct Space-to-Time Mapping of Metasurface Structures.

We experimentally demonstrate the generation of double terahertz (THz) pulses with tailored angular-dependent time delays from a nonlinear metasurface excited by a near-infrared femtosecond pulse. The tailored temporal properties of the generated pulses emerge from a direct mapping of the nonlinear spatial response of the metasurface to the emitted THz temporal profile. We utilize the Pancharatnam-Berry phase to implement symmetric and antisymmetric metasurface configurations and show that the emitted patterns present spatiotemporal "X-shaped" profiles after collimation by a parabolic mirror, with angular-dependent pulse delays corresponding to the intended design. In addition, we show that the addition of polarization multiplexing presents the opportunity to achieve a full range of elliptical THz polarizations. Double pulse generation and spatiotemporal shaping of THz waves in general show potential for THz spectroscopy and molecular dynamics applications, particularly in pump-probe experiments.

Complete light polarization control using a chiral-nematic cell with tangential-conical boundary conditions

Light polarization control by the chiral-nematic cell with hybrid tangential-conical boundary conditions has been studied by means of photo- and electrically induced transformations of the orientational structure. The polarization azimuth changes due to the power ratio of ultraviolet and blue radiations, at which the director twist angle in the chiral nematic varies smoothly. The light polarization ellipticity is controlled by an electric field applied perpendicular to the liquid crystal cell changing the effective anisotropy of the refractive index. The optical material under study is promising to develop the devices for the light polarization converter over the entire visible range, as well as for photo-controlled rotators of linear polarization of white light.

Simultaneous measurement of polarization rotation angle and ellipticity at the quantum noise limit

An experiment has been proposed for laser polarization signal measurement, with the rotation angle and ellipticity being measured simultaneously. The proposed experiment is immune to signal-to-noise ratio degradation due to the finite extinction ratio of polarizing elements used to construct the composite polarization measurement setup. Noise analysis is carried out to show that the proposed scheme allows one to reach the quantum noise limit in the simultaneous measurement of the polarization angle and ellipticity. This work should be of great interest for experiments such as observation of vacuum magnetic birefringence, spin-orbital interaction, material characterization, polarization microscopy, or biomedical optics.

Effect of wave polarization on ionospheric Ohmic heating and optimal polarization

The paper starts from the polarization of the electromagnetic wave launched by the transmitter, develops an ionospheric heating model for a wide range of launching angles and polarizations of powerful heating radio waves. The electric field polarization is characterized by Q and ϕ, where Q characterizes the relative amplitude of the electric field components and ϕ characterizes the relative phase of the electric field components. We use similarity transformation and tensor calculation in our calculations and give the optimal polarization equation using the idea of finding the maximum value of a binary function. Combining the ionospheric background data of three widely separated locations—EISCAT (polar region), Beijing (mid-latitude), and Sanya (low latitude)—we have numerically calculated and discussed the three sites based on the heating model. The following conclusions are drawn from the calculations. The Q of the optimal polarization gradually decreases and tends to be stable when the collision frequency becomes negligible relative to the ionospheric cyclotron frequency. Q also depends on the angle between the radio wave launching angle and the magnetic inclination angle. The optimal polarization angle ϕ is generally π/2 in northern hemisphere heating experiments. With the angle between the radio wave launching angle and the magnetic inclination angle increasing from 0, the optimal polarization changes from left-handed circular polarization to left-handed elliptical polarization, and when it reaches π/2, the optimal polarization becomes east–west linear polarization. These results will provide some guidance in future experiments.

Generation of Light Fields with Controlled Non-Uniform Elliptical Polarization When Focusing on Structured Laser Beams

We study the sharp focusing of the input structured light field that has a non-uniform elliptical polarization: the parameters of the ellipse depend on the position in the input plane (we limited ourselves to the dependence only on the angular variable). Two types of non-uniformity were considered. The first type corresponds to the situation when the semi-axes of the polarization ellipse are fixed while the slope of the major semi-axis changes. The second type is determined by the situation when the slope of the major semi-axis of the polarization ellipse is constant, and the ratio between the semi-axis changes (we limited ourselves to the trigonometric dependence of this ratio on the polar angle). Theoretical and numerical calculations show that in the case of the first type of non-uniformity, if the tilt angle is a multiple of the polar angle with an integer coefficient, then the intensity distribution has rotational symmetry, and the energy flow is radially symmetric and has the negative direction near the optical axis. In this second case, the intensity symmetry is not very pronounced, but with an odd dependence of the ratio of the semi-axes of the polarization ellipse, the focused field at each point has a local linear polarization, despite the rather complex form of the input field. In addition, we investigate the distribution of the longitudinal component of the Poynting vector. The obtained results may be used for the formation of focused light fields with the desired distributions of polarization, Poynting vector density, or spin angular momentum density in the field of laser manipulation and laser matter interaction.

The Mechanism of the Formation of the Spin Hall Effect in a Sharp Focus

We have shown how the spin Hall effect is formed in a tight focus for two light fields with initial linear polarization. We have demonstrated that an even number of local subwavelength regions appear in which the sign of the longitudinal projection of the spin angular momentum (the third Stokes component) alternates. When an optical vortex with topological charge n and linear polarization passes through an ideal spherical lens, additional optical vortices with topological charges n + 2, n − 2, n + 1, and n − 1 with different amplitudes are formed in the converged beam. The first two of these vortices have left and right circular polarizations and the last two vortices have linear polarization. Since circularly polarized vortices have different amplitudes, their superposition will have elliptical polarization. The sign of this elliptical polarization (left or right) will change over the beam cross section with the change in the sign of the difference in the amplitudes of optical vortices with circular polarization. We also have shown that optical vortices with topological charges n + 2, n − 2 propagate in the opposite direction near the focal plane, and together with optical vortices with charges n + 1, n − 1, they form an azimuthal energy flow at the focus.

Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus

AbstractShocklets and short large‐amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady‐state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach‐number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.

Tunable birefringence and elliptical polarization eigenmodes in a biplate of two quarter-wave plates.

Birefringence of elliptical polarization eigenmodes can be conceptualized as a composite system comprising two distinct media: one with linear polarization eigenmodes and the other with circular polarization eigenmodes. However, the practical realization of such a system often involves the combination of two birefringent quarter-wave plates (QWPs). In this study, our objective is to characterize the variable retardation and variable elliptical polarization eigenmodes exhibited by a biplate consisting of two quarter-wave plates. Additionally, we aim to analyze the geometric properties of the transformation of one state of polarization on the Poincaré sphere, employing the emerging state's curve. This curve corresponds to the intersection between the Poincaré sphere and a cone. The outcomes of our study are presented as a function of the angle between the fast axes of the two QWPs. The findings have the potential to contribute to the configuration of q-plates and facilitate the development of quantum communication protocols.

Extending the capabilities of vectorial ptychography to circular-polarizing materials such as cholesteric liquid crystals.

The problem of imaging materials with circular-polarization properties is discussed within the framework of vectorial ptychography. We demonstrate, both theoretically and numerically, that using linear polarizations to investigate such materials compromises the unicity of the solution provided by this computational method. To overcome this limitation, an improved measurement approach is proposed, which involves specific combinations of elliptical polarizations. The effectiveness of this strategy is demonstrated by numerical simulations and experimental measurements on cholesteric liquid crystal films, which possess unique polarization properties. With the help of Pauli matrices algebra, our results highlight the technique's ability to discern between the different types of circular polarizers, uniform vs. non-uniform, and determine their handedness.

Metasurface‐Based Orbital Angular Momentum Multi‐Dimensional Demultiplexer and Decoder

AbstractLight beams possess various dimensions, such as wavelength, spin angular momentum (SAM), and orbital angular momentum (OAM), which are indispensable in numerous optical applications. However, traditional techniques entail multiple attempts to disclose desired optical information, utilizing unwieldy multi‐pass systems or mechanically moving parts that are cumbersome to integrate into compact and integrated optical systems. Here, a single‐layer dielectric metasurface platform is proposed that enables multi‐dimensional demultiplexing and decoding, circumventing the need for conventional bulk optical elements. The platform can demultiplex 3D light parameters (wavelength, SAM, and OAM) and focus them at distinct spatial positions on a designated focal plane, providing a superior alternative to far‐field beams for integration with optical fiber and communication chips. The study verifies 132‐bit independent channels for a multi‐dimensional demultiplexer and demonstrates the metasurface‐based component's ability to function as an elliptic polarization decoder through a 4‐bit elliptic polarization coding transmission experiment. This work provides a compact and efficient platform for demultiplexing multi‐dimensional SAM and OAM states over a broad wavelength range, with potential implications for optical communications, optical data storage, optical information encryption, and quantum information sciences.

Polarization states and far-field optical properties in dielectric photonic crystal slabs.

We study the role of topological singularities like Bound States in a Continuum (BICs) or Circularly Polarized States (CPSs) in determining ellipticity of the far-field polarization in dielectric metasurfaces. Using finite-difference time-domain as well as rigorous coupled-wave analysis simulations, we determine the behavior of the Stokes parameter S3 in the whole k space above the light cone, with special regard to the region close to the singularities. Moreover, we clarify the relation between the topological singularities and the circular dichroism in reflectivity.