Laguerre-Gaussian Beams 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.

Saturated absorption spectroscopy of 87Rb atoms using structured light: Observation of narrow hyperfine and crossover resonances

Abstract An experiment on the saturated absorption spectroscopy (SAS) of 87Rb-D2 line is performed using the Laguerre-Gaussian (LG) beam as structured light. The theoretical simulation of which is done by considering a four-level atom-laser coupled system. The theoretically simulated spectra fairly match with the experimentally observed spectra. The line-width narrowing behavior of both the observed hyperfine and crossover resonances in the Doppler-broadened probe absorption spectra is attributed by the spatially dependent Rabi frequency of the pump LG beam irrespective of the characteristics of the probe beam. The results also illustrated that the narrowing behavior of the line shapes of the hyperfine structure using the LG beam is universal in nature, i.e. irrespective of hyperfine or crossover transitions. This structured light-induced narrowing of line-width of the sub Doppler hyperfine and crossover resonances can be utilized for high-precision laser frequency locking at a particular hyperfine or crossover transition. Moreover, a significant narrowing of hyperfine and crossover resonances with the variation of the orbital angular momentum (OAM) number of the LG beam shows that the generated SAS signal can be manipulated by using the OAM of the structured light as a control knob.

Angular Bloch oscillations and their applications

Abstract To advance inertial navigation, we present the scheme for a compact quantum sensor which is based on the quantum phenomenon of the angular Bloch oscillations and measuring exclusively the angular acceleration of slow external rotation. We study the dynamics of ultra-cold atoms confined in a toroidal trap with a ring-lattice along the azimuth angle, realized with the superposition of two copropagating Laguerre–Gaussian beams. In the presence of external rotation with a small angular acceleration, or a prescribed linear chirp between the two beams, the measured angular momentum of the trapped atoms exhibits a specific periodic behaviour in time, which we call as the angular Bloch oscillations. This quantum phenomenon is shown to be a key element of fruitful applications for (i) an efficient transfer of quantized angular momentum from the light to the atoms by controlling the chirp, and (ii) the direct determination of the angular acceleration of external rotation by measuring the Bloch period.

Coded communication study of Laguerre–Gaussian vortex beam and its superposition states in underwater turbulence

Using theoretical and experimental approaches, we have investigated coded communications for the Laguerre–Gaussian (LG) beam and its superposition states in an oceanic turbulent environment. We established an ocean turbulence transmission model and constructed an underwater vortex beam-coded communication experiment, generating light-intensity images of the LG beam and its superposition states transmitted in different simulated ocean turbulence environments. These simulated and experimentally obtained light-intensity images were grayed out, detected and identified, symbol coded, and decoded by the Visual Geometry Group neural network to study the bit error rate (BER) of the LG beam and its superposition states for coded communication in the simulated ocean turbulence environment. The study results show that the BER increases with increasing transmission distance and simulated ocean turbulence intensity. This study provides an important reference for the further development of optical communication and network technology in high-speed data transmission and communication capability enhancement.

Induction of orbital currents and Kapitza stabilization in superconducting circuits with Laguerre-Gaussian microwave beams

We investigate the effects of a Laguerre-Gaussian (LG) beam on the superconducting state. We show that the vortex angular momentum of a LG beam affects the superconducting state and induces currents. The induction of the current by microwave radiation is illustrated on a Josephson loop and SQUID devices. In particular, we establish that coupling a dc SQUID to the ac magnetic flux of a LG beam can stabilize the π phase in the SQUID. This can happen via developing a global or local minimum in the effective potential at π. In the latter case, this happens via the Kapitza mechanism. Published by the American Physical Society 2024

Elegant dihedral beams

Abstract Elegant Hermite-Gauss beams are a well-known family of structured beams. Although Siegman proposed them several decades ago, their properties continue to be studied and exploited. In this work, a group theory-based framework that introduces new classes of symmetric elegant beams is presented. Our formulation exploits the algebraic properties of the dihedral group of rotations and reflections to transform an input beam into a closed-form family of interference patterns with dihedral symmetry. Our approach is inspired by one of the outcomes of this work: elegant Hermite-Gauss beams can be described as a dihedral interference pattern of elegant traveling waves, a new set of solutions to the paraxial equation also developed in this paper. Taking elegant traveling waves as input beams, they are transformed into what we have called elegant dihedral beams. They have dihedral-symmetric transverse profiles and quasi-crystalline properties, including features like phase singularities, self-healing, and pseudo-nondiffracting propagation, as well as containing elegant Hermite and Laguerre-Gauss beams as special cases.

Talbot-effect-based multiplication of Laguerre–Gaussian beams with non-zero radial indices: From theory to experimental realization

We present a Talbot self-imaging inspired method for multiplying Laguerre-Gaussian (LG) beams of non-zero radial indices. We explore theoretically and experimentally the LG beam diffraction from two-dimensional (2D) periodic structures. In particular, we determine near-field LG diffraction patterns from a 2D binary grating of a small opening ratio (OR). We demonstrate that incident LG beam intensity patterns are reproduced as images of individual square apertures of the grating in certain Talbot planes. We also investigate the impact of the number of fractional-Talbot and Talbot planes on the quality of the generated 2D array of multiplexed LG modes. Our theoretical predictions are in good agreement with our experiments. Our method can find applications in optical communication, optical tweezing, multi-particle trapping, screening, and micro-manipulation.

Revealing the propagation dynamic of a Laguerre-Gaussian beam with two Bohm-like theories

By employing x-Bohm theory and p-Bohm theory, we construct the position and momentum trajectories of single-mode and superposed-mode Laguerre-Gaussian (LG) beams. The dependence of divergence velocity and rotation velocity on the initial position and propagation distance is quantified, indicating that LG beams exhibit subluminal effects, even in free space. Additionally, we clarify the formation of the petal-shaped intensity distribution of the superposed-mode LG beam in terms of motion trajectory, where the particle-like trajectory and wave-like interference are “simultaneously” observed. Our work provides an intuitive way to visualize the propagation characteristics of LG beams and deepen the comprehension of Bohm-like theory.

Theoretical analysis of on-axis obstructed Laguerre-Gauss beams

Theoretical analysis of on-axis obstructed Laguerre-Gauss beams

Azimuthally Modulating Surface Plasmon Polaritons

Abstract We suggest a scheme for the lossless excitation of surface plasmon polaritons (SPPs) at a metal-dielectric interface using a Laguerre Gaussian (LG) beam. We consider a three-layer structure consisting of a top transparent medium, a middle metal thin film, and a dielectric bottom layer. The dielectric medium contains three-level atoms exhibiting electromagnetically induced transparency (EIT). By applying a control field, a LG beam, and a microwave field, we induce azimuthally varying permittivity, which leads to the azimuthal modulation of SPPs. The propagation length of SPPs is increased when excited by a LG beam carrying optical angular momentum (OAM). Moreover, the group velocity of SPPs can be effectively controlled by adjusting the OAM and azimuthal angle of the LG beam, allowing for both slow and fast propagation of SPPs.

Theory of angular momentum transfer from light to molecules

We present a theory describing the interaction of structured light, such as light carrying orbital angular momentum, with molecules. The light-matter interaction Hamiltonian we derive is expressed through couplings between spherical gradients of the electric field and the (transition) electric multipole moments of a particle of any nontrivial rotation point group. Our model can therefore accommodate an arbitrary complexity of the molecular and electric field structure, and it can be straightforwardly extended to atoms or nanostructures. Applying this framework to rovibrational spectroscopy of molecules, we uncover the general mechanism of angular momentum exchange between the spin and orbital angular momenta of light, molecular rotation, and its center-of-mass motion. We show that the nonzero vorticity of Laguerre-Gaussian beams can strongly enhance certain rovibrational transitions that are considered forbidden in the case of nonhelical light. We discuss the experimental requirements for the observation of these forbidden transitions in state-of-the-art spatially resolved spectroscopy measurements. Published by the American Physical Society 2024

Twists through turbidity: propagation of light carrying orbital angular momentum through a complex scattering medium

We explore the propagation of structured vortex laser beams-shaped light carrying orbital angular momentum (OAM)-through complex multiple scattering medium. These structured vortex beams consist of a spin component, determined by the polarization of electromagnetic fields, and an orbital component, arising from their spatial structure. Although both spin and orbital angular momenta are conserved when shaped light propagates through a homogeneous, low-scattering medium, we investigate the conservation of these angular momenta during the propagation of Laguerre–Gaussian (LG) beams with varying topological charges through a turbid multiple scattering environment. Our findings demonstrate that the OAM of the LG beam is preserved, exhibiting a distinct phase shift indicative of the ‘twist of light’ through the turbid medium. This preservation of OAM within such environments is confirmed by in-house developed Monte Carlo simulations, showing strong agreement with experimental studies. Our results suggest exciting prospects for leveraging OAM in sensing applications, opening avenues for groundbreaking fundamental research and practical applications in optical communications and remote sensing.

Effect of evanescent wave on vector vortex beams on higher-order Poincaré sphere

Abstract Based on the vector angular spectrum representation, the contributions of the propagating and evanescent waves to the vector vortex Laguerre–Gaussian beams on the higher-order Poincaré sphere are investigated in the nonparaxial regime. The evolution properties of the propagating and evanescent waves are closely related to the topological charge, the radial order, the ellipticity angle, and the waist width. The influences of the evanescent waves on the intensity, the spin and orbital angular momenta of the vector vortex beams are discussed in detail.

Amplification of rotary photon drag using Laguerre-Gaussian beam of control field

Amplification of rotary photon drag using Laguerre-Gaussian beam of control field

Analysis of plasma wakefield generation by a Laguerre-Gaussian laser beam in laser-plasma accelerators with external injection

This study presents a comprehensive modeling of wakefield generation through external injection utilizing a Laguerre–Gaussian (LG) laser beam in a bubble/blowout regime. The wakefield dynamics are simulated in two dimensions using the particle-in-cell (2D-PIC) method via Wake-T tool, aiming to investigate the underlying mechanisms and characteristics of this process. The simulation results provide insights into the behavior of electrons within the wakefield, their acceleration, phase spaces of the electron beam, velocity distribution, and longitudinal and transversal profiles of the laser electric field in the plasma. The presented model serves as a valuable tool for further investigations into wakefield generation with external injection using LG laser beams, facilitating advancements in this field of study.

In-situ aberration correction for Laguerre-Gaussian optical tweezers via optimization of orbit shape

We introduce a concept of aberration correction under microscopy that is based on observation of circular Brownian motion of an object driven by orbital angular momentum of a Laguerre-Gaussian (LG) beam. Following the concept, we establish an aberration-correction scheme by using a holographic optical tweezers setup equipped with a spatial light modulator that produces the LG beam as well as corrects the light wavefront. The light wavefront is modified adaptively to improve circular symmetry and uniformity of the orbit of a colloidal dielectric sphere revolving in mid-water under the irradiation of the LG beam. We reveal that the proposed scheme is sensitive to tiny phase difference of less than the accuracy of a highest-grade optical flat, 0.05λ, and is applicable to aberrations of up to the first 21 terms of the Zernike series expansion. The scheme not only improves the quality of optical tweezers but also enables to distinguish individual objective lenses assigned a common product code from difference in aberration-correction patterns. The present contribution therefore provides a useful tool for microscopy and laser fabrication in addition to the immediate application to optical trapping.

Robustness of highly complex radial carpet beams in turbulent atmospheres

In this study, we report observations of propagating radial carpet beams (RCBs) through a turbulent atmosphere at ground level with a 120 m path length. RCBs are a class of nondiffracting, accelerating, self-healing, and self-amplifying beams, and generated in the diffraction of a plane wave from amplitude/phase radial gratings having different spoke numbers. Observations were made at different times of the day. The intensity profile of an RCB becomes complicated when the number of grating spokes used to generate the beam is large, and includes high intensity spots, called main intensity spots (MISs), which are symmetrically placed at the central area around the beam axis and whose number is equal to (twice) the number of spokes of the amplitude (phase) grating used to generate the beam. With the aid of a telescope and a CCD camera, successive frames of the intensity pattern of the RCBs having different levels of structural complexity are recorded at the end of the path. For the data recorded at different times of the day, we calculate the variance of displacements of MISs along the radial direction. We observe that displacements of the MISs increase with increasing mean temperature of the air; on the other hand, as the complexity of the beam intensity pattern increases, the displacements of the MISs decrease. In order to compare the resilience of different RCBs and a well-known structured beam against atmospheric turbulence, we investigate deformation of the intensity profiles of a Laguerre–Gaussian (LG) beam having a topological charge 20 and different RCBs at the end of the path. It is shown that under the same turbulence condition, highly complex RCBs are more resilient to the destructive effects of the atmospheric turbulence. In particular, for the RCBs generated with gratings having 30 spokes and more, the number of MISs of the received intensity patterns is changed by less than 1% even when the turbulence strength is high. But for the LG beam, its intensity ring is clearly broken in different places, which makes it impossible to follow its maximum intensity in the radial direction

Spectropolarimetric properties of vortex retarders

Vortex retarders are optical retarders with a uniform retardance, but with a fast axis that varies azimuthally over the area of the optic. This affects the radial and azimuthal polarization components of the incoming beam. The vortex retarders discussed here generate TEM10 and TEM20 Laguerre-Gaussian beams. While several varieties of these vortex retarders exist, designed to function at specific wavelengths, and a few studies have reported their use at those wavelengths, almost no data exists detailing their polarimetric properties outside those wavelengths. Using a Mueller matrix spectropolarimeter with dual-rotating retarders, the polarization properties of four zero-order half-wave vortex retarders have been measured across a broad wavelength range of 300–1100 nm. This data contributes to a more complete description of the spectral properties of these popular retarders.

Mapping structured Laguerre–Gaussian beam states onto the orbital Poincaré sphere in the form of controllable spatial trajectories

The structured Laguerre–Gaussian (LG) beam is a two-parameter superposition of 2n+ℓ+1 Hermite–Gaussian modes (where n and ℓ are a radial number and a topological charge of the initial LG beam) whose orbital angular momentum oscillations are controlled by phases and amplitude parameters. But we succeeded in reducing its representation to a simple sum of a standard LG mode and a hybrid Hermite–Laguerre–Gaussian (HLG) beam that is a key point in understanding a hidden geometry of the structured LG (sLG) beams and implementations of its unique prosperities. In assents, the hybrid HLG beam is mapped onto the orbital Poincaré sphere in the form of a plane trajectory along a main meridian of the sphere. However, the most intriguing thing is as follows. First, once we slightly perturb the HLG beam with a single LG mode, the flat trajectory turns into a complex multi-petalled tracery with multiple self-intersections due to cyclic variation of the phase parameter of the sLG beam. Moreover, the shape of the tracery as well as the birth and destruction of the self-intersection points can be controlled with the amplitude parameter. However, it is worth noting that when changing the beam parameters cyclically, the area outlined by the trajectory on the sphere is directly related to the geometric phase acquired by the sLG beam that can be treated as an additional degree of freedom for transmitting big data. In the article, we study the sLG beam properties and its mapping onto the orbital Poincarè sphere in the framework of a symplectic 4×4 matrix formalism while the orbital Stokes parameters are experimentally measured, and we have found good agreement between theory and experiment.

Interference of high-order perfect optical vortex beams

We investigate the interference of high-order perfect optical vortex (POV) beams with different topological charges. Through numerical simulations, we reveal a remarkable phenomenon: keeping the beam width, and beam radius fixed while changing the topological charge, the splitting of the composite POV beam into two distinct individual perfect vortices occurs exactly at the same inter-axial separation. The observed interference pattern exhibits pronounced sensitivity to factors such as axial separation, phase shift, beam radius, and topological charges of the constituent beams. Notably, our findings are contrasted with the interference of high-order Laguerre-Gauss (LG) beams, highlighting that the splitting of composite vortices into their individual components is more rapid in the case of LG beams. We also investigate the evolution of the interference pattern for both POV, and LG beams along the propagation direction in free-space. Our research provides significant insights into the distinct interference properties of high-order POV beams, presenting potential applications in the fields of optical manipulation and communication systems.