arXiv subjects

S. S. Ghaffari-Oskooei

Publications and source records attributed to S. S. Ghaffari-Oskooei.

8 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

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

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↗

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

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↗