Laguerre-Gaussian Laser Beams Research Articles

Nanoscale Helical Optical Force for Determining Crystal Chirality.

The deterministic control of material chirality has been a sought-after goal. As light possesses intrinsic chirality, light-matter interactions offer promising avenues for achieving non-contact, enantioselective optical induction, assembly, or sorting of chiral entities. However, experimental validations are confined to the microscale due to the limited strength of asymmetrical interactions within sub-diffraction limit ranges. In this study, a novel approach is presented to facilitate chirality modulation through chiral crystallization using a helical optical force field originating from localized nanogap surface plasmon resonance. The force field emerges near a gold trimer nanogap and is propelled by linear and angular momentum transfer from the incident light to the resonant nanogap plasmon. By employing Gaussian and Laguerre-Gaussian incident laser beams, notable enantioselectivity is achieved through low-power plasmon-induced chiral crystallization of an organic compound-ethylenediamine sulfate. The findings provide new insights into chirality transmission orchestrated by the exchange of linear and angular momentum between light and nanomaterials.

Laguerre-Gaussian Laser Beam Second Harmonic Generation in Arrays of Vertically Aligned Carbon Nanotube

Laguerre-Gaussian Laser Beam Second Harmonic Generation in Arrays of Vertically Aligned Carbon Nanotube

Collective effect of preformed plasma channel and plasma density ramp on second harmonic generation of Laguerre–Gaussian laser beam in plasma

Collective effect of preformed plasma channel and plasma density ramp on second harmonic generation of Laguerre–Gaussian laser beam in plasma

Vortex harmonic generation in indium tin oxide thin film irradiated by a two-color field.

When a two-color Laguerre-Gaussian laser beam propagates through an indium tin oxide (ITO) material, the spatial distributions of odd- and even-order vortex harmonics carrying orbital angular momentum (OAM) are studied. The origin of vortex harmonics can be directly clarified by investigating their dependence on the incident laser field amplitude and frequency. In addition, it is shown that the spectral intensities of vortex harmonics are sensitive to the epsilon-near-zero nonlinear enhancing effects and the thickness of ITO materials. Thus the vortex harmonics can be conveniently tunable, which provides a wider potential application in optical communications based on high-order OAM coherent vortex beams.

Excitation of electron plasma wave by self-focused Laguerre–Gaussian laser beams in axially inhomogeneous plasma: effect of orbital angular momentum of photons

Excitation of electron plasma wave by self-focused Laguerre–Gaussian laser beams in axially inhomogeneous plasma: effect of orbital angular momentum of photons

Self-focusing of Laguerre–Gaussian laser beams in collisionless plasma: paraxial-like approach

Self-focusing of Laguerre–Gaussian laser beams in collisionless plasma: paraxial-like approach

Self-focusing of low order LG laser beam in Gaussian plasma

Laguerre Gaussian (LG) laser beam propagations is presented to investigate the self-focusing in collision-less Gaussian plasma. This is by deriving the equations supporting self-focusing in plasma mediums by using WKB approximation. Additionally, a range of values of laser-plasma parameters which would fulfil these equations is considered. For the scenario of Gaussian and collision-less plasma, the study is contrasted. By utilizing a low order Laguerre Gaussian laser beam is more exciting as compare to using a Gaussian laser because it incorporates the propagation specific characters of Laguerre Gaussian Laser Beam. The observations are appeared in term of early self-focusing with LG laser beam. The investigation is expected to unfold the new and more effective scenario for self-focusing in plasma.

Study of particle acceleration by Laguerre–Gaussian ultra intense laser plasma interactions

In this work, simulations of multi-petawatt lasers in the range of ∼0.2 PW–∼100 PW with varying Laguerre–Gaussian (LG) azimuthal modes as well as linearly polarized (LP) and circularly polarized (CP) laser beams striking near critical density targets were studied by using three-dimensional particle in cell (PIC) codes. Particle acceleration mechanisms have a dependence on laser polarization and it affects the energy gained by the particles. It is known that laser pulses can be polarized helically by applying the LG distribution function to the fundamental Gaussian laser profile. In this study, differently polarized laser beams with varying powers were employed to study laser driven particle acceleration and compares accelerated charged particles’ energy spectra and angular distribution. It is seen that LG laser beams can accelerate higher energetic particles due to higher conversion efficiency compared to LP and CP laser beams. It is also seen that LG laser beams can collimate ions with a narrower spread compared to LP and CP beams. Furthermore, ions can have a smaller divergence angle with increasing azimuthal mode index when the laser is LG polarized. We also studied the energy deposition of these particles in a water cell obtained by the PIC codes for different laser parameters by using Geant4 Monte Carlo simulations which suggests that LG laser beam can be useful for the future hadron therapy applications.

Generation of tunable terahertz pulse carrying orbital angular momentum in non-uniform vortex plasma channel

An amplitude modulated Laguerre-Gaussian (LG) laser beam carrying orbital angular momentum (OAM) is considered for terahertz radiation using non-uniform plasma vortex channel under relativistic conditions. The suggested approach involves the exchange of angular momentum between a non-uniform vortex plasma and a laser beam. During the interaction of non-uniform vortex plasma with photons, the laser angular momentum changes and twisted terahertz radiation is generated. The resultant THz radiation is shown to be substantially dependent on the beam width parameter and non-uniformity in the plasma channel. The amplitude of THz increases with beam focusing and the orbital angular momentum parameter. Due to higher amplitude of THz this study is useful in THz applications like, detection of counterfeit drugs, explosive material, analyze and identify defects in materials, medical imaging and communication.

Laguerre-Gaussian beam and plasma interaction under relativistic and ponderomotive nonlinearities

Self-focusing of the laser plays a decisive role in achieving higher intensity. This article investigates the beam width evolution of the Laguerre-Gaussian laser beam in an underdense, cold, and collisionless plasma in the presence of weakly relativistic and ponderomotive nonlinearities. We consider pure radial mode of the LG beam (LG10) as it plays a key role in phenomenon like higher harmonic generation and can dominate diffraction effect in the self-focusing. Wentzel–Kramers–Brillouin (WKB) approach under paraxial approximation is used to reduce the nonlinear wave equation to a differential equation for the beam width parameter to study the self-focusing and defocusing phenomena. The optimum values of the initial intensity and beam waist of the laser beam are then calculated and plotted, for which the diffraction divergence is cancelled out by the self-focusing.

Role of fractional high harmonics with non-integer OAM on the generation of a helical attosecond pulse train.

Extreme-ultraviolet pulses of attosecond duration carrying orbital angular momentum (OAM) can be produced by spectrally filtering vortex high harmonics generated in a gas medium. Here we reveal that fractional high harmonics (FHHs) with non-integer OAM generated by a short duration Laguerre-Gaussian laser beam are origins for the change of helical attosecond pulse train (APT) with azimuthal angle. We show that these harmonics have gap and minimum structures in the annular intensity profile and discontinue phase distribution along azimuthal angle. And each FHH can be expressed as a superposition of OAM modes with integer topological charges. Features of FHH can be identified by coherently combining selected OAM modes. We also uncover that these features are formed after FHH is propagated in gas medium and in vacuum. We finally demonstrate that the generation of FHHs and the dependence of helical APTs on azimuthal angle are changed by varying the macroscopic condition.

Investigating pair-production by Breit–Wheeler process in a collisional plasma

Positrons have many potential applications in the field of high-energy nuclear and particle physics. For the generation of such high-energy positrons, we propose a mechanism via an interaction of optical vortex laser beams with collisional plasma. Based on the multiphoton Breit–Wheeler mechanism, the production of electron–positron pairs shows to be strongly dependent on the energy associated with the synchrotron radiation. Such radiations are emitted by accelerated charged particles in the plasma channel under quasistatic spontaneous magnetic field that confines the motion of the electrons. For the precise regulation of the accelerated positrons important quantities such as the probabilistic generation of positrons and the angular momentum of the plasma electrons are evaluated and discussed. It is observed that the use of the incident Laguerre–Gaussian laser beam helps to generate on-axis sheath formation to focus and accelerate the produced positrons.

Laguerre–Gaussian laser beam guiding and its second harmonics in plasma having density ramp

This paper presents the optical guiding of a laser beam in plasma by using a preformed plasma channel. The density ramp in plasma density due to the plasma pressure has also been considered. The effect of ponderomotive force has been taken into account which originates due to the intensity gradient present in the laser beam. This force produces a plasma gradient by expelling plasma electrons from a high-field to a low-field region, providing heavy ions remain immobile. Plasma oscillations result from a gradient in plasma density that excites an electron plasma wave. The equation governing the plasma wave excitation has been found by using linear perturbation theory. An in-phase mixing of an incident laser beam with this plasma wave generates its second harmonics. Laguerre–Gaussian laser profile has been used for harmonic production. Moment theory has been used to obtain a differential equation for beam waist, which has been solved numerically by Runge–Kutta's fourth-order method. The effect of different modes of Laguerre–Gaussian profile, beam intensity, plasma density, channel depth, and slope of density ramp has been explored.

Laser shaping and optical power limiting of pulsed Laguerre-Gaussian laser beams of high-order radial modes in fullerene C60

We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60 molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60 molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a non-centrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect; the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.

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.

Pattern formation and evidence of quantum turbulence in binary Bose-Einstein condensates interacting with a pair of Laguerre-Gaussian laser beams

We theoretically investigate the out-of-equilibrium dynamics in binary Bose-Einstein condensate confined within two-dimensional box potentials. One species of the condensate interacts with a pair of oppositely wound, but otherwise identical Laguerre-Gaussian laser pulses, while the other species is influenced only via the interspecies interaction. Depending on the number of helical windings (or the magnitude of topological charge), the species directly participating in the interaction with lasers is dynamically segmented into distinct parts that collide together as the pulses gradually diminish. This collision event generates nonlinear structures in the related species, coupled with the complementary structures produced in the other species, due to the interspecies interaction. The long-time dynamics of the optically perturbed species is found to develop the Kolmogorov-Saffman scaling law in the incompressible kinetic energy spectrum, a characteristic feature of quantum turbulence. This study warrants the usage of Laguerre-Gaussian beams for future experiments on quantum turbulence in Bose-Einstein condensates.

Influence of self-focused Laguerre-Gaussian laser beam on second harmonic generation in collisionless plasma having density transition

The influence of self-focused Laguerre-Gaussian beam (L-G beam) on second harmonic generation (SHG) in collisionless plasma with density transition is explored in present work. In presence of collisionless nonlinearity, the ponderomotve force causes redistribution of electrons thereby establishing transverse density gradients inside plasma. These density gradients causes production of electron plasma wave(EPW) at main beam frequency. The nonlinear interaction of EPW with main beam produces 2nd harmonics. The authors have employed the moment theory in order to obtain differential equation controlling the growth of beam waist and second harmonic yield (SHY). It is perceived from results that L-G beam modes and density transition play a major role in increasing beam’s focusing behavior and SHY.

Effect of orbital angular momentum of light on self-action effects of Laguerre Gaussian laser beams in collisionless plasmas

Nonlinear optical self-action effects like self-focusing, self-trapping of intense laser beams propagating through underdense plasmas have been investigated theoretically. The optical nonlinearity of the plasma has been modelled by ponderomotive force originating through intensity gradient over the cross section of the laser beam. In order to investigate the effect of orbital angular momentum of the photons on propagation characteristics of the laser beam, the irradiance over the cross section of the beam has been considered to be Laguerre Gaussian (LG). Effect of self-focusing of the laser beam on the evolution of its axial phase also has been investigated. Formulation is based on finding semi-analytical solution for the wave equation for the field of laser beam with the help of moment theory approach.

Enhanced self-focusing of Laguerre-Gaussian laser beam in relativistic plasma under exponential plasma density transition

In the current work, self-focusing of Laguerre-Gaussian laser beam under the influence of exponential plasma density transition in relativistic plasma is studied. It is observed that the spot size of laser beam shrinks as beam propagates into the plasma because of exponential plasma density ramp. The exponential plasma density ramp reduces the beam width parameter due to its slowly variation ramp profile. Also, with the rise in intensity of the laser beam, self-focusing enhances significantly. Our results in the present manuscript may be helpful in the field where strong self-focusing of the laser is required such as high-power laser driven fusion, explanation of devices involved in beam propagation in the various applications.

Chirality-enabled optical dipole potential energy for two-level atoms

We consider the optical dipole potential energy, which arises from the interaction of a two-level atom with a circularly polarized Laguerre-Gaussian laser beam of small waist. The beam is characterized by the existence of a longitudinal electric field component which is responsible for the appearance of a chiral term in the optical dipole potential energy. This term reverses sign if either the winding number or the wave polarization of the beam reverses sign. We propose a scheme of a bi-chromatic vortex interaction with the two-level atom in which the resulting optical dipole potential is fully chiral.