Plasma wakefield excitation driven by two color Laguerre Gaussian laser pulses carrying orbital angular momentum is investigated analytically and through quasi-cylindrical particle in cell simulations. Using a perturbative framework together with the quasistatic approximation, the influence of the transverse laser mode structure on the longitudinal and transverse wakefields in an underdense plasma is examined in the weakly relativistic regime. The results show that drivers with finite azimuthal index produce reduced and less regular on-axis longitudinal wakefields compared to conventional Gaussian drivers. However, radial longitudinal field distributions reveal that this reduction originates from a redistribution of the wakefield energy toward finite radii rather than a simple loss of wake excitation. Orbital angular momentum carrying modes generate hollow and ring shaped wake structures accompanied by strongly modified transverse electric fields and broader plasma density perturbations. Mixed Gaussian Laguerre Gaussian configurations exhibit intermediate behavior, combining weak on-axis acceleration with pronounced off axis wake excitation. The study demonstrates that structured two-color laser drivers fundamentally modify the topology of plasma wakefields and provide an additional mechanism for controlling transverse plasma dynamics, off-axis acceleration, and angular momentum mediated wakefield structures in plasma based accelerator schemes.

An analytical formulation of a radially polarized laser pulse propagating in a homogeneous, magnetized plasma is presented using Lorentz force, continuity, and Maxwell's equations. The perturbation technique and quasi-static approximation have been used to study the generated fields in a nonlinear regime. The generated slow, oscillating, transverse electric and magnetic fields (Eh and Br) having equal amplitude constitute a radiation field having frequency in the terahertz (THz) range. Particle-in-cell simulation code Fourier-Bessel particle-in-cell is used to validate analytical findings. Simulation studies also show that the generated THz radiation field propagates beyond the plasma boundary, indicating coherent electromagnetic radiation emission. Furthermore, the field amplitude scales nonlinearly with plasma density and increases linearly with external magnetic field strength, highlighting the role of these parameters in controlling radiation amplitude.

This study presents an investigation of second-harmonic generation (SHG) resulting from interaction of radially polarized laser beam propagating in homogeneous, unmagnetized plasma. Lorentz force and continuity equations have been used to derive the radial and axial current density components. Further, using these densities in the wave equation leads to analytical expressions for the SHG field amplitudes. These amplitudes exhibit periodic oscillations along the propagation axis, characterized by detuning length dependent on plasma density and laser parameters. Radial and axial contributions to SHG are found to be highly enhanced near the beam axis due to the Gaussian beam profile of the laser. The analytical findings are validated using Fourier-Bessel particle-in-cell (FBPIC) simulations. Notably, unlike linearly or circularly polarized beams which require either inhomogeneous or magnetized plasma, radially polarized beams facilitate efficient harmonic generation in homogeneous unmagnetized plasmas. Copyright c 2025 EPLA All rights, including for text and data mining, AI training, and similar technologies, are reserved.

We present an analytical and simulation study of twisted terahertz (THz) radiation generation through the propagation of a circularly polarized Laguerre–Gaussian laser pulse in homogeneous plasma embedded in an axial magnetic field. The analytical formulation is based on the perturbation technique and quasi-static approximation. Longitudinal and transverse wakefields generated via laser–plasma interactions are evaluated using the Lorentz force and Maxwell's equations in the mildly nonlinear regime. It is observed that two linearly polarized twisted THz radiation beams are generated in mutually perpendicular planes. The superposition of these two beams results in a single linearly polarized twisted THz radiation beam with modified amplitude and polarization direction. Three-dimensional particle-in-cell simulations are performed for this configuration using the Fourier-Bessel particle-in-cell code. A graphical comparison of the amplitude of the resultant THz beam, obtained from both analytical and simulation studies, is presented.

This paper deals with the evolution of longitudinal wakefields generated behind two-color asymmetric laser pulses through homogeneous plasma, using numerical model. The two laser pulses are linearly polarized and are assumed to have frequency difference equal to the plasma frequency. Laser pulses are either positively skewed or negatively skewed with respective asymmetric parameters. Combinations of asymmetric parameters are varied for two laser pulses to optimize the amplitude of wakefield. Maximum enhancement of wake amplitude is reported when both asymmetric laser pulses are positively skewed. Further, particle-in-cell simulations have been performed using Vsim code. The simulation study validates the results obtained via numerical model.

The paper presents a study of wakefield generation and electron injection via propagation of radially polarized laser pulses in homogeneous pre-ionized plasma. The analytical study is based on Lorentz force and continuity equations. Perturbation technique and quasi-static approximation are used for evaluating the generated longitudinal wakefields. Trapping and acceleration of electrons are examined by injecting a test electron in the generated wakefields. The results are compared with those obtained via linearly polarized laser pulses. The validation of analytical results is performed using the Fourier-Bessel particle-in-cell (FBPIC) simulation code. It is seen that there is a significant enhancement in amplitude of the longitudinal wakefield generated and electron energy gain via radially polarized laser pulses as compared to linearly polarized laser pulse case.

A study of the generation of terahertz (THz) radiation by propagation of a circularly polarized laser pulse in a parabolic plasma channel is presented. The laser–plasma system is embedded in a uniform axial magnetic field. Transverse electric and magnetic wakefields are evaluated using a perturbation scheme and quasi-static approximation. Nonlinear plasma electron velocities arise along the longitudinal and transverse directions as a result of interaction with the laser pulse. This results in the generation of an electromagnetic wave oscillating at THz frequency. The frequency of the obtained THz radiation can be controlled using the plasma channel parameters and can be tuned by varying the transverse position of observation. The THz radiation amplitude is enhanced in the presence of the parabolic channel compared to the homogeneous plasma configuration. The possibility of obtaining a tunable range of THz frequencies is presented. The analytical results have been validated using three-dimensional particle-in-cell simulations.

This study deals with the generation of terahertz (THz) to near infrared (NIR) radiation fields using two-colour linearly polarized copropagating laser pulses having either counter or co-polarization state. The frequency difference between the two laser pulses is considered to be integral multiple of the plasma frequency. Perturbation technique and quasistatic approximation have been used to obtain radiation field equations. Analytical and two-dimensional particle in cell simulation studies of the proposed configuration show that the transverse and axial plasma electron velocities arising due to nonlinear coupling of the two pulses are responsible for generation of off-axis linearly polarized radiation fields which propagate through plasma into vacuum. The frequency of generated radiation is similar to 40 THz (similar to 60 THz), when the frequency difference of the laser pulses is two (three) times the plasma frequency. Analytical results are validated using VSim particle in cell simulation code.

A study of generation of wakefield and particle acceleration via propagation of linearly polarised, chirped, Gaussian laser pulse in preformed plasma channel is presented. Perturbation technique is used to separate slow and fast varying plasma electron velocities and density. Considering the laser pulse length and amplitude to be evolving along the propagation distance, nonlinear fluid equations are used to derive longitudinal electric wakefields at varying propagation distances for chirped as well as unchirped pulses. It has been seen that longitudinal wakefield amplitude generated by positively (negatively) chirped laser pulses is higher (lower) than the amplitude obtained by unchirped laser pulses. The wakefield amplitudes are optimized with respect to the propagation distance. Further, trapping and acceleration of electrons by the generated wakes, is analysed. Comparing the energy of an accelerated test electron using chirped and unchirped laser pulses, it is shown that positively chirped laser pulses are capable of accelerating test electron to maximum energy using minimum injection energy. Hence, highest energy gain can be obtained by propagation of positively chirped laser pulse in plasma.

This paper presents an analytical and simulation study of terahertz (THz) radiation generation using short, circularly polarized laser pulses propagating in plasma embedded in arbitrarily oriented magnetic field. Perturbation technique is used to obtain generated electric and magnetic wakefields within and behind the laser pulse. Coupling of components of the obliquely applied magnetic field with transverse and axial plasma electron velocities leads to the generation of linearly as well as elliptically polarized transverse electromagnetic radiation oscillating at THz frequency, under appropriate conditions. The amplitude of these fields and ellipticity of the elliptically polarized THz radiation can be varied with the help of the obliqueness of the external magnetic field. Analytical results are validated using VSim PIC simulation code.

Longitudinal and transverse wakefields generated by the propagation of short laser pulses in preformed plasma is an important mechanism that finds applications in plasma based particle acceleration schemes as well as Terahertz (THz) radiation generation. When short, high intensity laser pulses propagate in underdense plasma, the ponderomotive force arising due to the intensity gradients in the laser pulse, pushes the plasma electrons away from the region of high intensity. The displacement of electrons creates a local charge separation, with the massive ions forming a stationary background. The electrostatic restoring force generated by the space charge tends to restore the perturbed plasma electron density distribution, leading to oscillatory electron motion inside and behind the laser pulse. These plasma oscillations follow the laser pulse in the form of a wakefield [1]. The acceleration of charged particles by plasma based accelerators utilizes the concept of generation of plasma waves or longitudinal wakefields either driven by an electron beam as in the plasma wakefield accelerator (PWFA), first proposed by Fainberg in 1956 [2] and observed experimentally by Rosenzweig et. al [3], or by an intense laser pulse. Tajima and Dawson [4] were the first to propose the concept of laser-plasma based acceleration technique which included laser wakefield accelerator (LWFA) and the plasma beat wave accelerator (PBWA). The former uses the concept of acceleration of externally injected electrons by wakefields generated by compact, short, high intensity laser pulses propagating in plasma while the latter uses two conventional long (~100 ps) laser pulses of modest intensity (~10-10 W/cm). Another laser plasma based accelerator system is the self-modulated laser wakefield accelerator (SMLWFA), in which enhanced acceleration of the charged particles is achieved via resonant self-modulation of the laser pulse [5]. Another laser-plasma based application of great interest is the emission of terahertz radiation via laser plasma interaction [6]. The first experimental observation [7] of laser-plasma-produced THz emission was reported in 1994. It was attributed qualitatively to laser-driven electron plasma oscillations. It is well known that mode conversion between electron plasma waves and their electromagnetic counterparts can occur in plasma under certain appropriate conditions. For example, when a laser pulse propagates obliquely through a tenuous inhomogeneous plasma, THz emission with a frequency nearly that of the plasma is produced, provided the plasma density increases with distance along the laser propagation direction [8]. Laser field ionization resulting from propagation of a short laser pulse in a gas target can also lead to THz emission, if the leading and trailing edges of the incident laser pulse are highly asymmetric as in the case of a frequency-chirped pulse [9]. THz emission occurs since a high transverse net current is produced. Such transverse currents can also be generated in pre-ionized plasma. The possibility of THz radiation generation due to transverse wakefields produced by propagation of short laser pulses in magnetized, homogeneous plasma has also been reported [10]. This presentation will focus on the theory of wakefield generation via laser-plasma interaction. Analytical studies of two applications based on such wakefields in plasma, namely, laser wakefield acceleration (LWFA) and terahertz radiation generation in magnetized-plasma will be discussed. Simulation studies validating the possibility of terahertz radiation emission by wakefields in magnetized plasma [11,12] will also be presented.

An analytical study of intense radiation generation at second harmonic frequency, by a circularly polarized laser beam propagating in plasma, in presence of an obliquely applied magnetic field, has been presented. Considering a mildly relativistic regime, a perturbation scheme is used for evaluation of transverse components of current density. The current density oscillating at twice the fundamental frequency of the laser field, drives the second harmonic radiation. The amplitude of the circularly polarized second harmonic radiation is derived and its variation with obliqueness of the applied magnetic field is graphically depicted.

An analytical theory is developed for the generation of phase-matched third harmonic radiation by bichromatic laser beams obliquely incident on a vacuum-plasma interface. A new perspective on the phase-matching condition between the bichromatic laser pump and harmonic fields has been presented. It is shown that phase matching can be achieved by varying the relative angle of incidence of the two laser beams. Phase-matched harmonic radiation generated by two-colour beams with linear, circular and elliptic polarization have been investigated and compared.

This paper deals with a two-dimensional simulation study of terahertz radiation emission in the wake of circularly polarized laser pulses propagating in uniformly magnetized plasma, using the XOOPIC code. The external magnetic field is applied along the direction of propagation of the laser pulse. It is seen that linearly polarized terahertz radiation is emitted off-axis, along the propagation direction, in plasma. This emitted radiation is also seen to be transmitted in vacuum. Simulation studies reveal that no such radiation is generated on-axis for the given configuration.

A theoretical model is developed for studying the generation of third-harmonic radiation by the interaction of obliquely incident, two-color p-polarized laser beams with spatially varying plasma density. The ratio of the fundamental frequencies of the two laser beams are considered to be an arbitrary integer. The amplitude of harmonic radiation obtained by oblique incidence of two-color laser fields propagating in homogeneous plasma is enhanced in comparison with that obtained by normal incidence of two-color laser beams. The periodicity of the plasma density allows the harmonic radiation to be phase-matched, leading to further increase in the amplitude of phase-matched harmonic radiation by an order of magnitude. The amplitude of the generated harmonic radiation increases with the increase in angle of incidence.

The evolution of the spot size and amplitude of a circularly polarized laser beam propagating in a plasma channel embedded in an obliquely applied magnetic field has been investigated. The wave equation describing the evolution of the radiation field is set up and a variational technique is used to obtain the equations governing the evolution of the spot size and amplitude. Numerical methods are used to analyze the evolution of the laser beam spot size and amplitude. It is seen that the amplitudes of the two transverse components of the electric field of the laser beam evolve differently, since they are driven by unequal current densities. This leads to the conversion of a circularly polarized laser beam into an elliptically polarized beam, under appropriate conditions.