Self-focusing Of Beam Research Articles

Self-focusing of q-Gaussian beam in unmagnetized plasma and its impact on second harmonic generation

Self-focusing of q-Gaussian beam in unmagnetized plasma and its impact on second harmonic generation (SHG) is explored in present work. Here, relativistic nonlinearity is taken in to consideration. The charge carriers get redistributed on account of relativistic nonlinearity. Further, the intensity gradients are generated in transverse direction to propagation of beam. Electron plasma wave (EPW) gets excited at frequency of input wave as a result of these intensity gradients. Excited EPW and input beam interacts nonlinearly thereby producing second harmonics (SHG). The second order ODE for beam width and expression for yield of SHG are derived by adopting WKB & paraxial ray approximations. The established laser and plasma parameters are used for acquiring numerical solutions for these equations. The beam’s ability to focus and SHG yield gets improved with increment in intensity of beam, beam radius, plasma density and q-values.

Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

THz generation by self-focused Gaussian laser beam in the array of anharmonic VA-CNTs

THz generation by self-focused Gaussian laser beam in the array of anharmonic VA-CNTs

Experimentally determined critical power for self-focusing of femtosecond vortex beams in air by a fluorescence measurement.

The filamentation of the femtosecond vortex beam has attracted much attention because of the unique filamentation characteristics, such as annular distribution and helical propagation, and related applications. The critical power for self-focusing of the femtosecond vortex beams is a key parameter in the filamentation process and applications. But until now, there is no quantitative determination of the critical power. In this work, we experimentally determine the self-focusing critical power of femtosecond vortex beams in air by measuring fluorescence using a photomultiplier tube. The relation between the self-focusing critical power and the topological charge is further obtained. Our work provides a simple method to determine the self-focusing critical power not only for vortex beams but also for Airy, Bessel, vector, and other structured laser beams.

Self-Focusing and Defocusing of Lorentz-Gauss Laser Beam in Collisionless Plasma

Self-Focusing and Defocusing of Lorentz-Gauss Laser Beam in Collisionless Plasma

Strong self-focusing of an intense cosh-Gaussian laser beam in magnetized plasma under relativistic effect

Strong self-focusing of an intense cosh-Gaussian laser beam in magnetized plasma under relativistic effect

Optical Force of Bessel Pincer Light-Sheets Beam on a Dielectric Sphere of Arbitrary Size.

In the framework of Generalized Lorenz-Mie theory (GLMT), based on the expansion results of electromagnetic field radiation components of Bessel pincer light sheets beam acting on dielectric particles of arbitrary size, the expression of radiation force components in a Cartesian coordinate system is obtained by using the Maxwell stress tensor method. On the one hand, the effects of the refractive index and the equivalent radius of spherical particles on the distribution of radiation force are discussed; On the other hand, the influence of beam scaling parameter and beam order of Bessel pincer light sheets beam on the distribution of radiation force are investigated. The results indicate that the changes of particle's refractive index and effective radius only affect the distribution of radiation force. However, the beam scaling parameter and beam order of Bessel pincer light sheets beam have a very sharp impact on the convergence position, distribution range and bending degree far away from the wave source of the radiation force. Single-beam optical tweezers using the self-focusing and self-bending Bessel pincer light-sheets beam are crucial for applications such as single molecule biophysics, optical manipulation and particle separation/clearing.

Influence of self-focused high power Cosh-Gaussian beam on second harmonic generation in cold quantum plasma

The objective of present work is to investigate influence of self-focused high power Cosh-Gaussian (ChG) beam on second harmonic generation (SHG) in cold quantum plasma (CQP). WKB and Paraxial approximations are utilized for acquiring 2nd order differential equation representing propagation characteristics of ChG beam with normalized propagation distance. The modification in dielectric function of plasma is observed on account of relativistic nonlinearity causing self-focusing of ChG beam. The density gradients are produced in transverse direction. These density gradients cause electron plasma wave (EPW) excitation at main wave frequency. Further, the nonlinear interaction between pump wave and excited EPW produces 2nd harmonics in plasma. We have performed numerical simulations for exploring impact of various laser & plasma parameters on beam waist of ChG beam and conversion efficiency of 2nd harmonics. We have also made the comparison of given work with classical relativistic plasma (CRP) regime.

Generation of superthermal electrons by self-focused Cosh Gaussian laser beams in inertial confinement fusion plasma

Generation of superthermal electrons by self-focused Cosh Gaussian laser beams in inertial confinement fusion plasma

Turbulence-resistant self-focusing vortex beams

We consider recently introduced self-focusing fields that carry orbital angular momentum (OAM) [2021 Opt. Lett. 46 2384–87] and in particular, their propagation properties through a turbulent ocean. We show that this type of field is especially robust against turbulence induced degradation, when compared to a completely coherent beam. In moderately strong oceanic turbulence, the self-focusing OAM beam features over five orders of magnitude higher peak intensities at the receiver plane, an ∼80% detection probability for the signal mode, as well as an energy transmission efficiency in excess of 70% over a link of ∼100 m. Counter-intuitively, the focusing properties of such fields may be enhanced with increasing turbulence, causing the mean squared waist to become smaller with greater turbulence strength. Our results demonstrate that certain types of partial coherence may be highly desirable for optical telecommunication employing OAM.

Second harmonic generation of zeroth-order Bessel-Gaussian laser beam in collisionless plasma

The objective of present work is to investigate second harmonic generation (SHG) of zeroth-order Bessel-Gaussian (B-G) laser beam in collisionless plasma. The ponderomotive force produces density gradients in plasma by expelling the plasma electrons from high field portion to low field portion thereby modifying plasma’s refractive index. This modification causes self-focusing of main beam. The density gradient further causes excitation of electron plasma wave (EPW) at the main beam frequency. The excited EPW couples with input beam thereby generating second harmonics. The well known WKB approximation and moment theory are employed for obtaining non-linear differential equation for laser beam’s spot size and expression for SHG yield. Further, numerical solutions of these equations are obtained by well known RK-4 method. It has been concluded from the present analysis that transverse component of wave parameter μ, normalized laser intensity and plasma density plays a significant role in affecting laser beam self-focusing and its SHG yield. Results from the present study are important for the laser induced plasma.

Characterization of Pseudospark Discharge-Based Multigap Plasma Cathode Electron Source for the Generation of Short Pulsed Energetic Electron Beam

Pseudospark (PS) discharge-based devices are known as excellent source for the generation of high current density and energetic self-focused electron beam in the hollow cathode (HC) phase. In this article, short pulsed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!\!\!&lt; 100$ </tex-math></inline-formula> ns) and high energetic (~20 keV) electron beam has been generated and propagated (up to ~60 mm) in the drift region without using any external guiding magnetic field from the four-gap configuration of PS discharge-based plasma cathode electron (PD-PCE) source. The particle-in-cell (PIC) simulation code OOPIC Pro has been employed, whose results have shown the strong dependence of beam propagation into the drift region on the penetration and distribution of potential lines. The combined experimental and simulation investigations have also been carried for the multigap (four-gap) with wide range of external storage capacitor (40 pF–18 nF) and operating voltages (5–35 kV). The circuit parameter controls the appearance of HC phase for the energetic (50%–70% applied voltage) electron beam and conductive phase for the high current (~10 A to ~0.5 kA) electron beam. The potential distribution has clearly indicated that the electron beam with higher applied voltages can propagate more focused in the drift region. The investigations have evidently shown the generation of low energy and high current to high energy and low current electron beams suitable to cover the potential applications in the field of extreme ultraviolet (EUV)/soft X-ray radiation generation, surface modification, and microwave-terahertz radiation generation.

Relativistic-ponderomotive effect on the self-focusing of a high-intensity cosh-Gaussian laser beam in plasma: higher-order paraxial regime

Relativistic-ponderomotive effect on the self-focusing of a high-intensity cosh-Gaussian laser beam in plasma: higher-order paraxial regime

Electron plasma wave excitation by self-focused cosh gaussian laser beams in axially inhomogeneous plasma: effect of density ramp

Electron plasma wave excitation by self-focused cosh gaussian laser beams in axially inhomogeneous plasma: effect of density ramp

Effect of Asymmetry in the Modulation Parameters on Self-Focusing of Asymmetric Finite Airy-Gaussian Laser Beam in Collisionless Plasma

The self-focusing/defocusing of asymmetric finite Airy-Gaussian (AiG) laser beam has been investigated by employing standard Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations in a nonrelativistic regime for underdense plasma. The second-order non-linear coupled differential equations have been solved numerically by using the fourth-order Range-Kutta method. The effect of asymmetry in the modulation parameters on the self-focusing/defocusing of the asymmetric finite AiG laser beam in collisionless plasma has been studied. It is observed that the self-focusing/ defocusing of asymmetric finite AiG laser beam is strongly connected with the initial values of the laser and plasma parameters such as modulation parameters and plasma frequency.

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

Effect of self-focusing of an intense cosh-Gaussian laser beam on second harmonic generation in a collisionless plasma: Higher-order paraxial theory

This paper presents the study of second harmonic generation in a collisionless plasma by an intense self-focused cosh-Gaussian laser beam under the combined effect of relativistic and ponderomotive nonlinearities. The second harmonics of a cosh-Gaussian laser beam is generated by the excitation of an electron plasma wave at the pump frequency. The excited electron plasma wave coupled with the pump laser beam and generate the radiation of double frequency. This study is carried out in a higher-order paraxial ray approximation where higher order terms are taken into account in the expansion of the dielectric function and the eikonal. Nonlinear differential equations have been established for the self-focusing of cosh-Gaussian laser beam in the plasma, the generation of electron plasma wave at the pump frequency, and the second harmonic generation. Numerical simulations have been carried out to investigate the effects of laser and plasma parameters such as decentred parameter (b), incident laser intensity (a), and relative plasma density (ωp0/ω0) on the self-focusing of the cosh-Gaussian laser beam and the electric field associated with electron plasma wave and second harmonic wave. A well-established set of laser and plasma parameters have been used in numerical analysis. The results show that the focusing of the cosh-Gaussian laser beam leads to an increase in the electric field of the electron plasma wave and the second harmonic wave. The results are also compared to the paraxial-ray approximation. The focusing of the cosh-Gaussian laser beam in the plasma is strengthened in the higher-order paraxial region, which increases the electric field of both the electron plasma wave and the second harmonic wave at high values of b, a, and ωp0/ω0.

Self-Focusing of Gaussian Laser Beam in an Axially Magnetized Plasma

A well established parabolic equation approach to study the evolution of self-focusing of Gaussian laser beam in underdense, magnetized plasma has been presented. The uniform external magnetic field is assumed to be applied along (forward) as well as opposite (reverse) to the direction of propagation of laser beam. The nonlinear differential equation governing dimensionless beam-width parameter is derived under WKB and paraxial approximations. It is observed that forward (reverse) magnetic field increases (decreases) the self-focusing of Gaussian laser beam as compared to the unmagnetized case of reference.

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Relativistic self-focusing of cosh-Gaussian laser beams in a warm quantum plasma

This paper presents an investigation of the self-focusing of cosh-Gaussian laser beams in warm quantum plasma while taking into account the effects of relativistic nonlinearity. The non-linear differential equation governing the beam width parameter under the weakly relativistic nonlinearity in this study was derived from the cylindrical coordinate system. The equation has been solved numerically by using the fourth-order Runge–Kutta method. Numerical analysis has shown that the present model's parameters, such as the decentered parameter, laser intensity, electron density of plasma, and Fermi temperature of electrons, play a vital role in propagation characteristics. Furthermore, comparisons were made for the cosh-Gaussian laser self-focusing in warm quantum plasma, cold quantum plasma, and classical relativistic plasma. It has also been found that the cosh-Gaussian laser beam has caused better focusing in the warm quantum plasma in comparison with the Gaussian laser beam; a fact that is very important for some applications in high-power laser-dense plasma interactions.