Self-focusing Of Beam Research Articles

Spatially nonuniformly correlated vortex beams and their arrays

We introduce a class of partially coherent sources with spatially nonuniformly correlation properties and an off-axis helicoidal phase. It is shown that the unique correlation and phase properties of such sources lead to radiated fields with extraordinary propagation characteristics, such as dark hollow with zero central intensity, self-focusing and lateral self-shifting light intensity. Based on such novel random sources, two types of nonuniformly correlated vortex beam arrays with radial and rectangular symmetry are explored. Analytical and numerical investigations for the evolutions of such light fields are made by the model decomposition representation of correlation function and fast Fourier transform method. The results demonstrate new opportunities for modeling off-axis self-focusing vortex beams and other beam shaping applications by joint modulation of coherence and phase.

Investigation of the Parameters of a Self-Focused Electron Beam Outputted Behind the Anode of a Vacuum Diode

Investigation of the Parameters of a Self-Focused Electron Beam Outputted Behind the Anode of a Vacuum Diode

Resonant second-harmonic generation of self-focused oblique incident laser beam in plasma

The present manuscript aims to realize the effect of self-focusing on second-harmonic generation (SHG) by oblique incident laser beams in plasma. When an intense laser beam is obliquely incident on the plasma, it is resolved into reflected and refracted components, and resonant SHG is produced in the reflected component on account of the self-focusing of the incident laser. With the help of paraxial approximation, we have obtained a mathematical expression for the beam width parameter and for the normalized amplitude of the second harmonic. It has been observed that the amplitude of the second-harmonic pulse is significantly influenced by the intensity of the incident laser beam, the wiggler magnetic field, and the normalized plasma frequency. The analysis was performed for different values of the angle of incidence and laser parameters. The results show stronger self-focusing and, hence, efficient SHG when the angle of incidence is the critical angle.

Propagation of intense catastrophe beams in air

This study uses numerical simulations to investigate the propagation of intense catastrophe beams in air. Our focus was on beams with high intensity below 1×1014W/cm2, which can cause the ionization of neutral atoms in air and create plasma paths. Due to the interaction between the Kerr effect, the self-focusing property of the catastrophe beam, and the defocusing caused by plasma, the propagation dynamics of the beam become very complicated. We analyzed three types of catastrophe beams with inward or outward main rings: ring Airy, ring Pearcey, and ring swallowtail. Additionally, our study also examined how these three self-focusing beams carrying orbital angular momentum behave in a plasma medium.

An Experimental Determination of Critical Power for Self-Focusing of Femtosecond Pulses in Air Using Focal-Spot Measurements

The filamentation of femtosecond pulses has attracted significant attention, owing to its unique characteristics and related applications. The self-focusing critical power of femtosecond pulses is one of the key parameters in the filamentation process and its application. However, the experimental determination of this power remains a challenging task. In this study, we propose an experimental approach to investigating the critical power for self-focusing of both femtosecond Gaussian and vortex beams with relatively low topological charges by analyzing the changes in the focal spot at different propagation distances. Our work offers a practical and convenient method for determining the self-focusing critical power of femtosecond pulses.

The influence of a self-focused laser beam on the stimulated Raman scattering process in collisional plasma

The influence of a self-focused beam on the stimulated Raman scattering (SRS) process in collisional plasma is explored. Here, collisional nonlinearity arises as a result of non-uniform heating, thereby causing carrier redistribution. The plasma density profile gets modified in a perpendicular direction to the main beam axis. This modified plasma density profile greatly affects the pump wave, electron plasma wave (EPW) and back-scattered wave. The well-known paraxial theory and Wentzel–Kramers–Brillouin approximation are used to derive second-order ordinary differential equations for the beam waists of the pump wave, EPW and the scattered wave. Further to this, the well-known fourth-order Runge–Kutta method is used to carry out numerical simulations of these equations. SRS back-reflectivity is found to increase due to the focusing of several waves involved in the process.

Enhanced self-focusing of q-Gaussian laser beam in underdense plasma under the combined effect of density ramp and axial magnetic field

Enhanced self-focusing of q-Gaussian laser beam in underdense plasma under the combined effect of density ramp and axial magnetic field

The effect of density ramp on self-focusing of q-Gaussian laser beam in magnetized plasma

The effect of density ramp on self-focusing of q-Gaussian laser beam in magnetized plasma

Combined effect of plasma density ramp and wiggler magnetic field on self-focusing of q-Gaussian laser beam in underdense plasma

Combined effect of plasma density ramp and wiggler magnetic field on self-focusing of q-Gaussian laser beam in underdense plasma

Evolution and particle trapping dynamics of circular Pearcey-Airy Gaussian vortex beams in tightly focused systems.

This study investigates the propagation and evolution of self-focusing circular Pearcey-Airy Gaussian vortex beams (CPAGVB) through high numerical aperture objective lenses. CPAGVB demonstrates a unique light field distribution compared to the circular Pearcey vortex beam and circular Airy Gaussian vortex beam. By adjusting optical distribution factors, main radii, and off-axis vortex pair positions, a variety of light field structures can be generated, including asymmetric micro-optical bottles, quasi-flat-top beam micro-optical bottles, and dual optical bottles. The particle trapping performance of CPAGVB is examined, revealing a gradient force eight orders of magnitude larger than its scattering force, up to twice the peak gradient force, and 2.5 times the scattering force of CAGVB. Further analysis of lateral power flow density, spin density vector, and total angular momentum distribution at the focal plane unveils the dynamics of particle motion toward the center. The Gouy phase difference under varying main radii reveals two types of normalized spin density vectors, characterized by helical and oscillating distributions. Additionally, the study examines the two-dimensional polarization ellipse distribution at the focal plane, elucidating the formation of central polarization singularities with axial vortices and the impact of peripheral polarization rearrangement on phase singularities. This research advances the comprehension of CPAGVB's distinctive properties and potential applications in micro-optical systems and particle manipulation.

Manipulating self-focusing beams induced by high-dimensional parabolic umbilic beams

The excellent property that the intensity of autofocusing beams in the focal plane increases exponentially, makes them especially beneficial for biomedical treatment. We experimentally generate tunable (2+1)-dimensional circular parabolic umbilic beams (CPUBs) for the first time based on the high-dimensional diffraction catastrophe integral, which is determined by the potential function. Such CPUBs have circular and symmetrical intensity distributions in space through radial symmetry transformation. Due to the flexibility of high dimensionality, these light beams have rich light field structures and self-focusing property. Where, the maximum intensity suddenly increases by orders of magnitude in the focal plane. Unlike the classical circular Airy beams, CPUBs exhibit multiple self-focusing points along the optical axis and a needle-like structure during propagation, which can be affected by manipulating the control parameters. The rich properties provide a new perspective for exploring the novel physical mechanisms and phenomena in autofocusing beams. The experimental results verify the correctness of the numerical simulations. CPUBs greatly enrich the autofocusing beam family and will be advantageous for medical treatments, optical micromanipulation, and microscopic imaging.

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 propagation of skew cosh Gaussian laser beam in attenuated magneto plasma

Self-focusing of a laser beam is one of the major consequences of nonlinear interaction of laser with plasma. In this paper, self-focusing of skew cosh Gaussian (skew-ChG) laser beam is studied in anisotropic, collisional plasma where in externally exponentially decreasing magnetic field is applied. Skewness parameters in the field profile of skew-ChG laser beam eventually determine intensity profile of the beam. The symmetry in skewness parameter in two transverse directions simplifies the calculations considerably. Second order, nonlinear, ordinary, coupled differential equations for Beam Width Parameters (BWP) are obtained using Akhmanovs approach under Wentzel–Kramers–Brillouin (WKB) and paraxial approximations which are solved numerically. For given amplitude of applied magnetic field, attenuated oscillatory self-focusing is observed with respect to change in attenuation coefficient.

Magnetically enhanced THz generation by self-focusing laser in VA-MCNTs

Magnetically enhanced terahertz (THz) radiations are generated on account of the self-focusing of the laser beam in the bunch of anharmonic Vertically Aligned Metallic Carbon Nanotubes (VA-MCNTs) embedded on the non-conductive sapphire or silicon on sapphire (SOS) substrate. The high-power Gaussian laser beam gets self-focused in the bunch of VA-MCNTs as the initial power of the propagating beam is greater than its critical power. The resulting laser beam interacts with the bunch of VA-MCNTs and as a result, the electrons of MCNTs experience a nonlinear ponderomotive force to show oscillatory behavior with resonant nonlinear transverse velocity. It produces the nonlinear current which drives the THz radiation generation. Enhanced THz generation is noticed in the regions where self-focusing becomes stronger. We have observed that an applied magnetic field, anharmonic behavior of MCNTs, self-focusing, and dimensions of MCNTs also pave the way for the enhancement of the normalized THz amplitude. The anisotropic behavior of the dielectric tensor in the presence of an externally applied static magnetic field also helps to enhance the THz amplitude. The results shown (by the beautiful graphs and well supported by the numerical simulation) in the present scheme indicate that the bunch of VA-MCNTs can play a diverse and significant role in the important applications of THz medical photonics by varying the values of various parameters. The emitted THz radiation has the ability to detect changes in the DNA of human beings because the frequency of the emitted radiation is observed to lie in the frequency region of molecular spectra of DNA and the corresponding energy of THz radiation is not high enough to damage the DNA by ionization.

Relativistic Self-Focusing of a q-Gaussian Laser Beam in Plasma by the Influence of Magnetic Field

Relativistic Self-Focusing of a q-Gaussian Laser Beam in Plasma by the Influence of Magnetic Field

Explosive Effervescence and Ablation of Polymethyl Methacrylate Under Irradiation with a Self-Focusing High-Current Electron Beam

Explosive Effervescence and Ablation of Polymethyl Methacrylate Under Irradiation with a Self-Focusing High-Current Electron Beam

Self-focusing of asymmetric finite Airy-Gaussian laser beams in magnetized plasma

In this work, the role of asymmetry in the beam profile of finite Airy-Gaussian (AiG) laser is presented to explore its propagation dynamics in collisionless magnetized plasma. Emphasis is on analyzing the self-trapping condition for both extraordinary (E) and ordinary (O) modes of propagation of AiG laser beam. Theoretical formulation is based on obtaining nonlinear coupled differential equations for beam-width parameters in both transverse dimensions of the beam with the help of parabolic equation approach under WKB and paraxial approximations. It is found that asymmetry in the modulation parameters significantly affects self-focusing of finite AiG beam. Moreover, the same initial intensity parameter for simultaneous self-trapping of both modes of propagation is noteworthy.

Generation of terahertz radiation by a Hermite–Gaussian laser beam inside magnetoplasma with a density ramp

In the present scheme of work, the Hermite–Gaussian (HG) laser beam dynamics has been investigated under the influence of an upward density ramp inside magnetized plasma, where both relativistic and ponderomotive nonlinearities are operative. One can achieve self-focusing of laser beam due to the change in the medium's dielectric function, which comes into operation due to the expulsion of plasma electrons from the high intensity to the low-intensity region by ponderomotive force and their motion at relativistic speeds. The dynamics of the laser beam and terahertz generation have been investigated by using the moment theory approach. It has been observed from the present analysis that the dynamics of the laser beam and the production of terahertz radiations strongly depends upon the HG laser beam and plasma parameters. In addition to this, the effect of density ramp and magnetic field has also been investigated on the efficiency of terahertz generation. It has been observed that higher-order modes of the HG laser beam play a dominant role in the production of terahertz radiations.

Self-focusing of a q-gaussian laser beam under the influence of an exponential plasma density ramp in plasma

The goal of the current manuscript is to investigate how a plasma density ramp affects the ability of a q-Gaussian laser beam (q-GLB) to self-focus in plasma. The laser beam exhibits oscillatory self-focusing and defocusing behaviour with increasing distance of propagation. We used an exponential plasma density ramp to combat this defocusing tendency, allowing the particular laser beam to achieve a minimal spot size and nearly retain it up to several Rayleigh lengths. In addition to that, it has been observed that self-focusing increases with increasing q-values and the laser intensity. However, the lower values of q suggest strong self-focusing. By warily selecting the plasma and laser parameters, the density ramp could play a key role in the self-focusing of q-Gaussian laser. Self-focusing is seen to become stronger as propagation distance increases and the q-parameter affects the behaviour of the beam-width parameter in the plasma as shown.

Effect of an external magnetic field on the self-focusing of a cosh-Gaussian laser beam in plasma under the relativistic-ponderomotive effect

This work presents an analytical and numerical study of the relativistic-ponderomotive effect on self-focusing of an intense cosh-Gaussian laser beam in a collisionless magnetized plasma by considering an external magnetic field in the direction of propagation of the laser beam. The nonlinear differential equation for the beam width parameter/intensity of a cosh-Gaussian laser beam in a magnetized plasma is obtained by Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations. The self-focusing of the cosh-Gaussian beam at different values of the magnetic field parameter is investigated. The results have also been compared to relativistic nonlinearity. The results show that the self-focusing effect of cosh-Gaussian beam in magnetized plasma becomes stronger, when relativistic and ponderomotive nonlinearities acts together. In addition, the self-trapping of cosh-Gaussian beam in magnetized plasma has also been studied. Numerical results are presented for the well-established laser and plasma parameters.