Polarized Laguerre Gaussian Research Articles

Polarization structure of optical vortices in inclined Laguerre–Gaussian beams passed through a uniaxial crystal

The work shows that in linearly polarized Laguerre–Gaussian beams passing through an anisotropic medium at an angle to the optical axis of the crystal, the distribution of optical vortices is devoid of axial symmetry. It is shown that the trajectories of movement of polarization singularities in the plane of the Laguerre–Gauss beam are different for different cases of input linear polarization at angles γ=±45∘ and there is an exchange of optical vortices, provided that the sign of the topological charge is preserved. It is shown that when the axis of an anisotropic medium is tilted, the movement of optical vortices occurs, accompanied by topological reactions of creation, destruction, or displacement of optical vortices to the periphery of the beam. It is characteristic that at angles of inclination by linear polarization γ=+45∘, topological reactions of creation and annihilation occur, and at angles γ=−45∘, topological reactions of displacement of optical vortices to the periphery of the beam occur.

Fine Structure of Optical Vortices in Linearly Polarized Laguerre–Gaussian Beams in Oblique Beams Propagating a Uniaxial Crystal

Traditional ideas about linearly polarized paraxial beam propagation along the optical axis of a uniaxial crystal suggest that at the crystal exit face, after propagation through the polarizer, the beam will form an intensity distribution in the form of a conoscopic pattern. Any violation of axial propagation was considered as a perturbation of the conoscopic pattern and was not taken into account. Nevertheless, this process opens up a wide variety of transformations of polarization singularities caused by weak perturbations. In this article, the behavior of linearly polarized low-order Laguerre–Gauss beams in a uniaxial crystal is considered. The existence of a fine structure of radiation on the output face of a uniaxial crystal and the dependence of this fine structure on the parameters of the crystal and the beam are shown.

Effects of primary aberrations on a dark-field microscopy imaging system with the sharper focusing lens

The effects of primary aberrations of the sharper focusing lens on the image quality is analyzed for a dark-field microscopy imaging system, which is illuminated by a left-circularly (LC) polarized Laguerre–Gaussian (LG) vortex beam. To confirm the aberration tolerance range of the sharper focusing lens for precise measurement, the analytical expression of the field distribution on the image plane is deduced. Then the dark-field image results corresponding to a defect with a scale of 6µm×6µm are simulated. The influence of the spherical error, coma, and astigmatism on the imaging quality is compared in detail. Then the verification test has been carried out to show the effects of different primary aberrations. Finally, both the simulation and experiment results help us to identify that the tolerance range of spherical aberration, astigmatism, and coma should be less than 1.5λ, 1λ, and 1.25λ, respectively.

Characteristics of electron beams accelerated by parallel and antiparallel circularly polarized Laguerre–Gaussian laser pulses

Characteristics of electron beams accelerated by parallel and antiparallel circularly polarized Laguerre–Gaussian laser pulses

Building Paraxial Optical Skyrmions Using Rational Maps

A simple mathematical expression based on rational maps to describe all optical paraxial skyrmion known to date, including Néel‐type and Bloch‐type skyrmions, bimerons, and anti‐skyrmions, is introduced. This expression is derived solely from topological considerations and outlines the rules that fully polarized paraxial light fields must obey to qualify as optical skyrmions. It is shown that rational maps can be implemented experimentally by superposing a pair of orthogonally polarized Laguerre–Gaussian modes. Novel optical skyrmion fields, called multi‐skyrmions, are obtained upon generalizing the proposed expression, laying the foundation for the exploration of skyrmion nucleation and annihilation mechanisms in optics.

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

The generation of a 33.7 W radially polarized output is demonstrated by way of double-pass amplification in a Ho:YAG thin-slab crystal. The amplifier system was seeded with the radially polarized output beam from a continuous-wave 13.2 W, 2.1 µm Ho:YAG rod laser, which exploited gain medium bifocusing and a ring-shaped pump spot to promote preferential lasing on the radially polarized Laguerre–Gaussian mode. By compensating for both the thermally induced stress birefringence in the thin-slab crystal and the Gouy phase shift resulting from astigmatic focusing of the 13.2 W seed, only marginal beam degradation was observed across the 95 W range of pump power into the amplifier.

Post-Flood UAV-Based Free Space Optics Recovery Communications with Spatial Mode Diversity

The deployment of unmanned aerial vehicles (UAVs) for free space optical communications is an attractive solution for forwarding the vital health information of victims from a flood-stricken area to neighboring ground base stations during rescue operations. A critical challenge to this is maintaining an acceptable signal quality between the ground base station and UAV-based free space optics relay. This is largely unattainable due to rapid UAV propeller and body movements, which result in fluctuations in the beam alignment and frequent link failures. To address this issue, linearly polarized Laguerre–Gaussian modes were leveraged for spatial mode diversity to prevent link failures over a 400 m link. Spatial mode diversity successfully improved the bit error rate by 38% to 55%. This was due to a 10% to 19% increase in the predominant mode power from spatial mode diversity. The time-varying channel matrix indicated the presence of nonlinear deterministic chaos. This opens up new possibilities for research on state-space reconstruction of the channel matrix.

Clarification for the fields of different radially polarized Laguerre-Gaussian light beams.

Radially polarized light beams have found many applications in particle manipulation, laser processing, and microscopy. Just as with linear polarization, radially polarized light beams can have higher-order transverse modes that involve Laguerre polynomials. Fields of a radially polarized Laguerre-Gaussian light beam have been calculated before, even beyond the paraxial approximation. However, there are in fact multiple solutions to the paraxial wave equation that involve Laguerre polynomials with different properties and propagation characteristics. We therefore clarify the discrepancies among three valid radially polarized solutions to the paraxial wave equation that involve Laguerre polynomials.

High order modes of intense second harmonic light produced from a plasma aperture

Because of their ability to sustain extremely high-amplitude electromagnetic fields and transient density and field profiles, plasma optical components are being developed to amplify, compress, and condition high-power laser pulses. We recently demonstrated the potential to use a relativistic plasma aperture—produced during the interaction of a high-power laser pulse with an ultrathin foil target—to tailor the spatiotemporal properties of the intense fundamental and second-harmonic light generated [Duff et al., Sci. Rep. 10, 105 (2020)]. Herein, we explore numerically the interaction of an intense laser pulse with a preformed aperture target to generate second-harmonic laser light with higher-order spatial modes. The maximum generation efficiency is found for an aperture diameter close to the full width at half maximum of the laser focus and for a micrometer-scale target thickness. The spatial mode generated is shown to depend strongly on the polarization of the drive laser pulse, which enables changing between a linearly polarized TEM01 mode and a circularly polarized Laguerre–Gaussian LG01 mode. This demonstrates the use of a plasma aperture to generate intense higher-frequency light with selectable spatial mode structure.

Bright γ-ray source with large orbital angular momentum from the laser near-critical-plasma interaction

We propose a new laser-plasma-based method to generate bright γ-rays carrying large orbital angular momentum by interacting a circularly polarized Laguerre–Gaussian laser pulse with a near-critical hydrogen plasma confined in an over-dense solid tube. In the first stage of the interaction, it is found via fully relativistic three-dimensional particle-in-cell simulations that high-energy helical electron beams with large orbital angular momentum are generated. In the second stage, this electron beam interacts with the laser pulse reflected from the plasma disc behind the solid tube, and helical γ beams are generated with the same topological structure as the electron beams. The results show that the electrons receive angular momentum from the drive laser, which can be further transferred to the γ photons during the interaction. The γ beam orbital angular momentum is strongly dependent on the laser topological charge l and laser intensity a 0, which scales as . A short (duration of 5 fs) isolated helical γ beam with an angular momentum of −3.3 × 10−14 kg m2 s−1 is generated using the Laguerre–Gaussian laser pulse with l = 2. The peak brightness of the helical γ beam reaches 1.22 × 1024 photons s−1 mm−2 mrad−2 per 0.1% BW (at 10 MeV), and the laser-to-γ-ray angular momentum conversion rate is approximately 2.1%.

Simultaneous Detection of Spin and Orbital Angular Momentum of Light through Scattering from a Single Silver Nanowire

AbstractIn recent times the spin angular momentum (SAM) and orbital angular momentum (OAM) of light have gained prominence because of their significance in optical communication systems, micromanipulation, and sub‐wavelength position sensing. To this end, simultaneous detection of SAM and OAM of light beam is one of the important topics of research from both application and fundamental spin‐orbit interaction (SOI) point of view. While interferometry and metasurface based approaches have been able to detect the states, the presented approach involves elastic scattering from a monocrystalline silver nanowire for the simultaneous detection of SAM and OAM state of a circularly polarized Laguerre–Gaussian beam. By employing Fourier plane (FP) microscopy, the transmitted scattered light intensity distribution in the FP is analyzed to reconstruct the SAM and OAM state unambiguously. The SAM and OAM induced transverse energy flow as well as the polarization dependent scattering characteristics of the nanowire is investigated to understand the detection mechanism. This method is devoid of complex nanofabrication techniques and to the authors' knowledge, is a first example of single nano‐object based simultaneous SAM and OAM detection. The study will further the understanding of SOI effects and can be useful for on‐chip optical detection and manipulation.

Electron pulse train accelerated by a linearly polarized Laguerre–Gaussian laser beam

Abstract A linearly polarized Laguerre–Gaussian (LP-LG) laser beam with a twist index $l = -1$ has field structure that fundamentally differs from the field structure of a conventional linearly polarized Gaussian beam. Close to the axis of the LP-LG beam, the longitudinal electric and magnetic fields dominate over the transverse components. This structure offers an attractive opportunity to accelerate electrons in vacuum. It is shown, using three-dimensional particle-in-cell simulations, that this scenario can be realized by reflecting an LP-LG laser off a plasma with a sharp density gradient. The simulations indicate that a 600 TW LP-LG laser beam effectively injects electrons into the beam during the reflection. The electrons that are injected close to the laser axis experience a prolonged longitudinal acceleration by the longitudinal laser electric field. The electrons form distinct monoenergetic bunches with a small divergence angle. The energy in the most energetic bunch is 0.29 GeV. The bunch charge is 6 pC and its duration is approximately $270$ as. The divergence angle is just ${0.57}^{\circ }$ (10 mrad). By using a linearly polarized rather than a circularly polarized Laguerre–Gaussian beam, our scheme makes it easier to demonstrate the electron acceleration experimentally at a high-power laser facility.

Rotation and Revolution of Optically Trapped Gold Nanorods Induced by the Spin and Orbital Angular Momentum of a Laguerre–Gaussian Vortex Beam

AbstractOptical trapping, spinning, and orbiting of nanoparticles allow the study of nanoscale mechanical, thermal, and optical effects. A circularly polarized Laguerre–Gaussian beam can simultaneously rotate a gold nanorod about its symmetry axis while revolving it around the beam's symmetry axis. The first motion is rotational in character, whereas the second is translational. Effective temperatures of each motion are experimentally obtained and compared with predictions from the Hot Brownian Motion theory. The results also show the optical‐to‐mechanical torque‐transduction efficiency to be equal for the spin and orbital angular momentum.

Evolution properties of partially coherent radially polarized Laguerre–Gaussian vortex beams in an anisotropic turbulent atmosphere

Analytical formulas for the cross-spectral density matrix of a partially coherent radially polarized Laguerre-Gaussian vortex (PCRPLGV) beam in anisotropic atmospheric turbulence are derived based on the extended Huygens-Fresnel principle. The evolution laws of statistical properties of a PCRPLGV beam in turbulence, such as the average intensity, degree of coherence (DOC) and degree of polarization (DOP), are investigated in detail. It is found that the atmospheric turbulence induces degeneration of the intensity distribution of a PCRPLGV beam on propagation, and some new properties, such as self-shaping and self-rotating, will appear on propagation due to vortex phase. In addition, in order to verify our theoretical results, we combined the complex screen method and multi-phase screens method to simulate the propagation of PCRPLGV beam in atmospheric turbulence. And the studies indicate that the simulation results are consistent with the theoretical predictions. Our results will be useful in some potential applications, such lidar detection, remote sensing and free-space optical communications.

Attosecond γ -ray vortex generation in near-critical-density plasma driven by twisted laser pulses

Ultra-short brilliant γ-rays have many potential applications in astrophysics, nuclear physics, and ultra-fast science. However, attosecond γ-ray beams with energy above 100 MeV are still very challenging. Here, we propose and numerically demonstrate an all-optical scheme to produce sub-GeV attosecond γ-rays in near-critical-density (NCD) plasma. When a left-hand circularly polarized Laguerre–Gaussian (LG) laser pulse irradiates the NCD plasma, dense attosecond electron bunches are produced, trapped by the LG laser, and accelerated to GeV energies. Subsequently, these electrons oscillate in the LG laser electric fields and emit a string of hundreds MeV attosecond (367 as) γ-ray pulses. Three-dimensional particle-in-cell simulations indicate that, at a laser intensity of 1022 W/cm2, the yield of γ-ray pulses with photon energies above 1 MeV is as high as 1013 with a peak angular momentum of 10−15 kg m2/s. This results in γ-ray vortex beams with an unprecedented peak brilliance of 1024 photons s−1 mm−2 mrad−2 per 0.1% bandwith at 1 MeV, which may offer a unique opportunity for diverse applications.

Isolated intense half-cycle attosecond pulse generation with orbital angular momentum

A relativistic linearly polarized Laguerre–Gaussian (LG) laser pulse interacting with a combination of gas plasma and an oblique foil target is proposed to generate an intense attosecond pulse carrying large orbital angular momentum (OAM). The LG laser pulse firstly produces an ultra-thin relativistic electron sheet (RES) in underdense plasma and transfers the OAM to the latter at the same time. When the RES passes through the oblique foil, it radiates an intense half-cycle attosecond pulse carrying large OAM. Three-dimensional particle-in-cell simulation confirms that an isolated ultra-intense half-cycle attosecond pulse with a duration of 542 as and a peak electric field of 5 × 1012 V m−1 is produced. The average OAM per photon of the attosecond pulse is about −1ћ. Such an intense, isolated attosecond pulse with the large OAM would provide new possibilities in attosecond scientific research.

Orbital angular momentum density characteristics of tightly focused polarized Laguerre-Gaussian beam.

The orbital angular moment (OAM) of light has been proved to be useful in plenty of applications. By transmitting the OAM of the focused light field to a particle, it will be orbited around the optical axis. Therefore, it is necessary to study the OAM distribution of the focused light field used to manipulate the particles. In this application, the widely used paraxial approximation is no longer sufficient due to the tightly focused beam. We employ the higher-order Poincaré sphere to represent the Laguerre-Gaussian (LG) beams with arbitrary polarization. Then the Rayleigh-Sommerfeld integral method and the q-parameter method are used to derive the analytical expression of the light field on the focal plane. Based on this, the OAM density expression of the tightly focused LG beam is derived. In the numerical simulation, we study and analyze the unique intensity distributions and OAM distributions of tightly focused linear polarized, radial polarized, and circular polarized LG beams. The results could be leveraged to further explore the applications of the polarized vortex beam.

Generation of energetic ring-shaped ion beam from relativistic Laguerre–Gaussian laser pulse interacting with micro-structure targets

By using three-dimensional particle-in-cell simulations, we demonstrate that an energetic ring-shaped ion beam can be generated by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse interacting with micro-structure targets. The electron and ion dynamics of three different targets including a sleeve–wire target, wire target, and common planar target are investigated. It is found that an optimized sleeve–wire target can provide a remarkable increase in the maximum ion energy and laser-to-ion energy conversion efficiency. The reason can be attributed to the matched transverse profiles between the electric-field distribution of Laguerre–Gaussian laser and sleeve–wire structure, resulting in efficient laser-target energy coupling. In fact, using a laser pulse of intensity 2.74 ×1020 W/cm2, duration 66.7 fs, and energy ∼1 J, one can obtain ∼35 MeV protons, ∼5.8 MeV/u carbon ions, and ∼15% laser-to-ion energy conversion.

Low-divergence relativistic proton jet from a thin solid target driven by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse

We propose a new ion acceleration scheme of irradiating a thin solid target with an ultraintense circularly polarized Laguerre–Gaussian (LG) laser pulse. Three-dimensional particle-in-cell simulations are performed to demonstrate that this scheme can generate a low-divergence high-density relativistic proton jet. By this scheme, the number of protons emitted with a small angle (<1°) from the laser axis can be more than tens of times as high as that of the protons accelerated by a circularly polarized Gaussian pulse. The inward ponderomotive force of the LG pulse drives such a proton beam along the laser axis.

Three-dimensional isotropic STED microscopy generated by 4[formula omitted] focusing of a radially polarized vortex Laguerre–Gaussian beam

In this study, a method is proposed to generate a three-dimensional (3D) isotropic super-resolution spot using stimulated emission depletion (STED) microscopy. A focused radially polarized Laguerre–Gaussian (LG01) beam is used as the pump beam. A focused depletion spot is produced by a radially polarized vortex Laguerre–Gaussian beam in a 4π focusing system. The influences of the topological charge, the order of LG, the maximum aperture angle, and the ratio of the pupil radius to the beam waist (β) on the spherical symmetry of the fluorescent spot are analyzed in detail. With the optimization parameters, an isotropic fluorescent spot is realized. The full widths at half maximum (FWHM) value of the isotropic fluorescent spot are 0.0348λ in both the r and z directions in a saturated case. The proposed model can provide a useful and simple guideline to obtain the spherical spot in 3D microscopy, which is very useful for trapping specific pathological ultra-structures of spherical shaped molecules and related medical applications.