arXiv subjects

F. M. Aghamir

Publications and source records attributed to F. M. Aghamir.

6 recordsLinked to original sources

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

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

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

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

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↗