arXiv subjects

A. A. Molavi Choobini

Publications and source records attributed to A. A. Molavi Choobini.

15 recordsLinked to original sources

arXiv2026

Second Harmonic Generation Through Backward Raman Scattering in Magnetized Plasmas Driven by Circularly Polarized Intense Lasers

A fluid-based theoretical framework is developed to describe the nonlinear cascade linking primary BRS-driven plasma wave amplification, oscillating two-stream instability (OTSI), nonlinear current generation within a self-formed ponderomotive channel, and radiation of the secondary electromagnetic mode. Systematic parameter studies reveal a strong sensitivity of the entire cascade to the relative handedness of laser polarization and axial magnetic field direction, as well as to cyclotron resonance strength. Resonant right-handed circular polarization significantly enhances ponderomotive expulsion, channel depth, BRS and OTSI growth rates, nonlinear current density, and the amplitude of the secondary harmonic, whereas non-resonant left-handed polarization effectively suppresses these processes. Fully kinetic particle in cell simulations using EPOCH, together with macroscopic finite-element modelling in COMSOL Multiphysics, corroborate the polarization- and magnetization dependent wake modulation and channelling efficiency across a wide range of laser wavelengths, pulse durations, and plasma densities. The temporal evolution and saturation of OTSI, resilience to density inhomogeneities, and wavenumber-resolved resonance tuning illustrate axial magnetization as a flexible control mechanism for adjusting the intensity, spectral position, bandwidth, and stability of multi peak Raman spectra. These findings demonstrate that cyclotron resonance and polarization control are effective methods for manipulating nonlinear Raman emission in high-intensity laser magnetized plasma interactions, offering predictive insights for forthcoming kinetic simulations and experimental implementations.

physics.plasm-ph↗

arXiv2026

Enhanced Harmonic Generation in Terahertz FELs: Influence of Pre-Bunching and Undulator Geometry on Spectral and Angular Emission

Both theoretical and numerical analyses are conducted to investigate terahertz (THz) radiation emission from free-electron lasers. The angular and spectral characteristics of radiation are analytically evaluated leveraging Linenard Wiechert field formalism, The analysis spanned across varying beam profiles and undulator parameters, including harmonic order, magnetic strength, period, and electron energy. Fourier analysis of the electric field reveals strong sensitivity of spectral content to underlying beam dynamics and undulator structure. Planar undulators tend to generate radiation with more prominent side lobes, especially at higher harmonics, while helical undulators produce narrower, more focused emission profiles. Importantly, the polarization and forward directed nature of the radiation are governed primarily by the resonant conditions and beam dynamics, rather than the undulator geometry itself. Building on these analytical insights, GENESIS simulations are employed to quantify the evolution of the bunching factor and radiation intensity under varying energy spread and plasma dispersion. The results show that increased undulator periods enhance radiation coherence, while transitions to wiggler regimes (at high magnetic parameters) lead to angular broadening and lateral lobe formation. Among all beam profiles studied Gaussian, Lorentzian, biGaussian, and prebunched the prebunched configuration demonstrates superior harmonic generation capabilities, albeit with high sensitivity to energy spread and plasma effects.

physics.acc-ph↗

arXiv2026

Spatiotemporal THz emission from radial and longitudinal wakefields by copropagating chirped lasers in magnetized rippled plasma

The excitation of radial and longitudinal wake-fields by two co-propagating chirped laser pulses in a rippled, magnetized plasma has been examined. This study aimed to clarify the spatiotemporal evolution of wake structures and assess their role in the generation of THz radiation. A Fourier-Bessel Particle-In-Cell (FBPIC) simulation framework, optimized for cylindrical geometries, has been employed to model the relativistic dynamics of plasma electrons under the combined influence of laser-induced ponderomotive forces and an external magnetic field. It has been shown that the beat frequency between the pulses modulates the ponderomotive force, driving nonlinear wake-field structures sustained by electron oscillations. Simulations performed with high spatial resolution have revealed that wake-field amplitude and coherence are strongly influenced by laser chirp, pulse duration, and plasma density. Distinct THz peaks have been identified in the Fourier-transformed spectra, with their amplitudes enhanced by resonant coupling between wake-field harmonics and the laser frequency modulation. Moreover, electron motion has been confined by the magnetic field, leading to improved energy gain and shaping of angular radiation patterns. These findings suggest that tailored laser and plasma configurations can be used to optimize energy transfer mechanisms, paving the way for more efficient wake-field usage and THz generation.

physics.plasm-ph↗

arXiv2026

Resonant RF Wakefield Coupling for Radiation-Reaction Control of 3D Betatron Dynamics in Hybrid Laser Plasma Accelerators

Hybrid laser plasma radiofrequency (RF) acceleration architectures signify a promising advancement in addressing the stability challenges associated with traditional laser wakefield accelerators. A thorough theoretical and numerical analysis of the three-dimensional dynamics of ultra-relativistic electron bunches in these hybrid systems is presented, clearly explaining how transverse beam stability, betatron oscillation polarisation, and radiative cooling work. By combining analytical models of spatiotemporal plasma wakefield modulation and phase dependent RF-driven oscillations with fully self-consistent 3D particle in cell (PIC) simulations, incorporating classical radiation reaction (RR) via the Landau Lifshitz model (with quantum parameter to account for synchrotron like losses during betatron oscillations. The findings indicate that the external RF fields operate as a tunable lattice, allowing for exact adjustment of amplitude, frequency, and carrier-envelope phase, which facilitates deterministic regulation of transverse focussing gradients and betatron amplitudes. A regime of resonant alignment between RF fields and natural betatron frequencies is established; this resonance enhances controlled transverse excursions while concurrently diminishing parasitic oscillations via increased radiative damping, resulting in substantial emittance reduction and the alleviation of synchrotron-like energy losses. Also, the detailed stability maps and 3D force landscapes show that the gamma factor growth rates change over time depending on the interaction between longitudinal field gradients and initial injection conditions. The paper's results give a clear picture of the nonlinear, resonant, and damping events that happen in hybrid accelerators. They also make it possible to get ultra stable, high-quality electron beams with the right polarisation states.

physics.acc-ph↗

arXiv2026

Mechanisms of THz Radiation Generation in Multi-Color Laser-Plasma Interactions: A Review Across Diverse Media

The exploration of Terahertz (THz) waves has captivated researchers across diverse scientific disciplines such as physics, spectroscopy, chemistry, biology, and engineering, driven by the myriad applications these waves offer. Within this expansive landscape, the development of efficient and reliable THz sources stands as a paramount objective. In the pursuit of this goal, a multitude of approaches have been undertaken, with a notable contender emerging in the form of laser-induced plasma. Harnessing the advancements in ultrafast pulses, laser-induced plasma has proven to be a promising tool for generating THz waves. Its appeal lies in the robust attributes of a high power threshold, intense THz signal, and an broadband THz spectrum. This paper delves into a comprehensive review of the physics and progress underlying THz generation from laser-induced plasmas, exploring scenarios where plasmas are induced in gases, liquids, and solids. The interactions between lasers and plasmas involve complex physical processes, resulting in a variety of laser plasma scenarios for THz generation. In this review, the focus is specifically placed on classifying THz generation based on different physical mechanisms and also examines the characteristics of the emitted THz waves. By categorizing the processes, a deeper understanding of the underlying principles can be attained.

physics.plasm-ph↗

arXiv2025

Terahertz Wave Generation in Two-Dimensional MXenes under Femtosecond Pulsed Laser Illumination

The efficient generation of terahertz (THz) waves in two-dimensional (2D) MXene layers driven by near-infrared femtosecond laser pulses is demonstrated through predictive simulations. Employing a novel hydrodynamic model that self-consistently captures nonlinearities from electric, magnetic, and convective interactions with a minimal set of material parameters. The coupled hydrodynamic-Maxwell equations are solved via finite-difference time-domain (FDTD) methods to resolve the spatiotemporal dynamics of laser-induced carriers and THz emission. The results reveal strong, tunable THz output dependent on laser (intensity, polarization, incidence angle), material (composition, carrier density, temperature), and struc-tural (layer thickness, substrate) parameters. These predictions offer verifiable guidelines for experiments and position MXenes as versatile platforms for compact, broadband THz sources in on-chip photonics and 6G communications. This work establishes a robust, self-contained framework for modeling ultrafast nonlinear optics in 2D materials.

physics.optics↗

arXiv2025

Tailored Three Dimensional Betatron Dynamics in UltraStable Hybrid Laser Plasma RF Accelerators

The detailed theoretical and numerical investigation of hybrid laser plasma RF accelerators, elucidating the mechanisms governing transverse beam dynamics, betatron polarization, and radiation reaction in ultra-relativistic electron bunches is presented. This framework combines analytical models of spatiotemporal plasma wakefield modulation, phase-dependent RF-driven oscillations, and quantum-corrected Landau Lifshitz radiation reaction with fully self-consistent 3D particle in cell simulations using EPOCH. The results demonstrate that RF amplitude, frequency, and phase enable precise control over transverse focusing strengths, betatron oscillation amplitudes, and polarization states. Resonant alignment between RF fields and natural betatron frequencies amplifies transverse excursions while damping parasitic oscillations through enhanced focusing gradients and radiation reaction, yielding reductions in emittance and mitigation of synchrotron-like energy losses. Stability maps and 3D force landscapes reveal strong phase sensitivity, where initial conditions and RF component ratios govern the temporal evolution of betatron amplitudes, and longitudinal field gradients modulate γ growth rates. These findings provide a comprehensive picture of nonlinear, resonant, and damping phenomena in hybrid laser plasma RF systems, highlighting the full spectrum of controllable transverse, longitudinal, and polarization dynamics in ultra relativistic electron beams.

physics.plasm-ph↗

arXiv2025

3D PIC simulation and theoretical modeling of RF Laser pulse in magnetized plasma for the generation of multidimensional relativistic Wakefields

The present study, investigates the modulation of plasma wakefields in dense magnetized plasma driven by relativistic electron beams under transverse RF excitation. A self consistent theoretical framework, comprising the RF vector potential, Maxwells equations, and relativistic electron motion, is extended through full 3D electromagnetic particle in cell simulations. The results reveal systematic amplification and reshaping of wakefields under the combined action of external magnetic fields and RF drivers. Variations in the cyclotron to plasma frequency ratio dictate the radial positioning and gyromotion of plasma electrons, sharpening transverse confinement and stabilizing blowout structures. The RF amplitude introduces progressive modulation of radial excursions and transverse forces, enhancing wakefield symmetry and depth. Current density distributions confirm the nonlinear scaling with RF strength, evolving from weak perturbations into sharply structured ion channels. Scalar potentials and longitudinal fields exhibit pronounced sensitivity to pulse shape, polarization angle, frequency ratio, and driver density, each parameter producing distinct oscillatory features and confinement regimes. Plasma density sets the field strength and radial localization, while the modulation parameter governs the emergence of fine scale oscillatory bands, producing smooth to multiband transitions in longitudinal electric fields. Across all conditions, simulations confirm the reinforcement of ponderomotive force, resulting in controlled narrowing of electron sheaths, sharper scalar potential gradients, and extended acceleration zones.

physics.plasm-ph↗

arXiv2025

Hydrodynamic PIC analysis of THz generation by two color laser in various plasma gases

In the present study, a theoretical and PIC numerical investigation of THz emission driven by two color femtosecond laser fields in gaseous plasmas is conducted. The model is formulated in cylindrical coordinates to capture the inherent radial symmetry of laser plasma interactions. Starting from a hydrodynamic description of plasma electrons coupled with Maxwells equations, the nonlinear photocurrent dynamics that underpin the emission process is derived. The results reveal that the asymmetry induced by the superposition of the fundamental and second-harmonic fields plays a central role in breaking inversion symmetry, thereby generating a net directional current that radiates in the THz regime. Systematic analysis demonstrates that gas composition, ionization fraction, and the intensity ratio of the two fields strongly influence both the spectral characteristics and efficiency of THz radiation.

physics.plasm-ph↗

arXiv2025

Forward Raman Scattering and Self-Modulation instabilities of lasers in magnetized tapered plasma channels

The propagation of laser pulses in tapered magnetized plasma channels is analyzed using the fluid theory of cold plasmas. This study focuses on laser propagation's key instabilities: forward Raman scattering and self-modulation instability. The influence of plasma density, laser intensity, dc magnetic field strength, and laser polarization on the growth rates of these instabilities is thoroughly examined. Analytical and numerical computations of the number of e-foldings for forward Raman scattering are performed to quantify its impact. The results reveal that increased plasma density and laser intensity significantly enhance the growth rates of these instabilities, leading to amplified Raman-scattered wave intensity and modulation of the laser envelope. Moreover, the strength of the dc magnetic field plays a pivotal role: it boosts instability growth rates for right-handed circularly polarized laser pulses while suppressing them for left-handed circularly polarized pulses. These findings highlight that reducing the growth rates of instabilities can facilitate the stable propagation of laser pulses in tapered plasma channels.

physics.plasm-ph↗

arXiv2025

Wakefield-induced THz wave generation in a hybrid dielectric-plasma cylindrical waveguide

In the present study, the generation of THz radiation through wakefield excitation in a cylindrical dielectric plasma waveguide is investigated. The proposed hybrid dielectric-plasma wakefield structure combines the advantages of dielectric materials and plasma, creating a versatile platform for high-performance applications and advanced THz radiation generation. By leveraging the strengths of both techniques, this hybrid configuration achieves enhanced gradients and optimized THz wave output. The mechanism involves a high-energy laser pulse propagating through a plasma-loaded dielectric waveguide, inducing wakefields that drive THz wave emission. This dual capability underscores the versatility of the proposed structure, offering significant advancements in THz wave generation technologies. To support the theoretical analysis, numerical simulations were employed using the Fourier-Bessel Particle-In-Cell (FBPIC) method and the COMSOL Multiphysics package. The simulation modeled the wakefield generation process and validated the propagation of electromagnetic waves. A comprehensive parametric study examined the effects of various parameters including dielectric thickness, an external DC magnetic field, laser pulse length, driver beam radius, and total current, on the wakefield generated THz radiation. Through systematic variation of these parameters, the study aims to elucidate the controlled features of the resulting fields and optimize THz radiation.

physics.plasm-ph↗

arXiv2024

Two-plasmon decay instability and 3/2 harmonic generation in inhomogeneous magnetized plasma

Two-plasmon decay instability emerges as the parametric decay of laser beams into two plasma waves which is expected for hohlraum in inertial confinement fusion. The behavior of this instability in magnetized plasma is investigated in the present study where the thermal effects are considered. The study demonstrates that the applying of a dc magnetic field significantly increases the rate at which the instability develops, while the increase of electron temperature has the opposite effect. The generation of 3/2 harmonic, which results from the beating of the incident laser and plasma wave, is also studied in the present study. The intensity of this harmonic, which appears in the spectrum as a sideband derived analytically, indicates that an increase in the dc magnetic field increases the intensity of this sideband.

physics.plasm-ph↗

arXiv2024

Generation of THz waves through interaction of the wakefield of two-color laser pulses with magnetized plasma

The present study explores radiation in THz spectrum region through the interaction of the wakefield of two-color laser pulses with magnetized plasma. The interaction of the two-color laser with plasma electrons induces transverse nonlinear current in two dimensions, resulting in generation of a wakefield and a forward wave. The investigation revealed that during the non-relativistic regime of laser-plasma interaction, interdependence exists between the electric fields of the forward wave and the wake. Conversely, in the relativistic regime, the dynamic of interaction changes, and plasma electrons are influenced not only by the electric field of the laser pulse but also by relativistic effects like Lorentz contraction, responding to both the electric and magnetic field components. This leads to generation of wake and forward wave radiations. The interplay between various laser and plasma parameters is analyzed, shedding light on the conditions leading to radiation angular distribution patterns in the forward and backward directions. The impact of spatial laser profile, a DC external magnetic field, polarization states, and plasma interaction length on the generated wake and forward wave patterns has been investigated. Through systematic variation of these parameters, the objective is to elucidate the controlled directional features of the resulting fields and radiation patterns.

physics.plasm-ph↗

arXiv2024

Investigation of self-focusing of Gaussian laser beams within magnetized plasma via source-dependent expansion method

Self-focusing emerges as a nonlinear optical phenomenon resulting from an intense laser field and plasma interaction. This study investigates the self-focusing behavior of Gaussian laser beams within magnetized plasma environments utilizing a novel approach, source-dependent expansion. By employing source-dependent expansion, we explore the intricate dynamics of laser beam propagation, considering the influence of plasma density and external magnetic fields. The interplay between the beam's Gaussian profile and the self-focusing mechanism through rigorous mathematical analysis and numerical simulations, particularly in the presence of plasma-induced nonlinearities are elucidated here. Our findings reveal crucial insights into the evolution of laser beams under diverse parameters, the ponderomotive force, relativistic factors, plasma frequency, polarization states, external magnetic field, wavelength, and laser intensity. This research not only contributes to advancing our fundamental understanding of laser-plasma interactions but also holds promise for optimizing laser-driven applications.

physics.plasm-ph↗

arXiv2024

Pulse-shaping in the interaction of an elliptically-polarized laser and magnetized-plasma

Pulse shaping provides a significant level of control and precision when optimizing laser-plasma interactions. Pulse shaping enables precise control and manipulation, resulting in enhanced energy deposition, optimized particle acceleration, controlled polarization, and exploitation of resonant effects. The present study investigates the interaction of structured light with magnetized plasma, considering various spatial profiles and polarization states. This phenomenon involves modification of the temporal and spatial characteristics of the laser pulse due to the presence of the magnetized plasma. The discussion reveals how the electric field and electron velocity evolve within the plasma both spatially and temporally. Factors such as absorption, dispersion, collisions, and scattering are taken into account to understand how they influence the evolution of the pulse. The effects of electron density, external magnetic fields, relativistic velocities, and polarization states on pulse compression are examined. The spatial laser profile impact on pulse-shaping and plasma channel formation is also discussed. This exploration sheds light on the intricate interplays and potential pulse-shaping applications in laser-plasma interactions.

physics.plasm-ph↗