arXiv subjects

G Ravindra Kumar

Publications and source records attributed to G Ravindra Kumar.

4 recordsLinked to original sources

arXiv2026

Quasi mono-energetic, relativistic electron acceleration in a femtosecond, high intensity laser excited solid magnet

The interaction of ultraintense lasers with magnetized overdense plasmas reveals a fundamentally new regime of laser-driven particle acceleration. Particle-in-cell simulations demonstrate the generation of directional, quasi-monoenergetic electrons in the MeV energy range superimposed on a broad thermal electron background with the estimated acceleration gradient of 3.6 MeV/μm, which is the highest till date. In contrast to conventional laser-plasma accelerators, which rely on underdense plasmas and are therefore constrained to relatively low plasma densities and limited beam charge, the present scheme operates in plasmas with densities orders of magnitude higher, opening new possibilities for the generation of high-flux energetic electron beams. A central result of this work is the demonstration of the excitation of electron Bernstein waves during relativistic laser interaction with magnetized overdense plasmas. The subsequent Landau damping of these electrostatic warm-plasma modes selectively transfers energy to resonant electrons, leading to the emergence of quasi-monoenergetic spectral peaks at energies that can be tuned through the applied magnetic field. To support the simulation results, we experimentally demonstrate the directional emission of energetic electrons from a simple permanent-magnet target irradiated by an ultraintense laser pulse, highlighting the practical feasibility of controlled electron-beam generation in dense plasma environments. These findings establish electron Bernstein waves as an efficient mediator of laser energy coupling in overdense plasmas and introduce a new paradigm for controlled particle acceleration and energy deposition in high-energy-density plasma systems.

physics.plasm-ph↗

arXiv2025

Impulsive excitation of a solid by extreme contrast, high intensity femtosecond laser pulses

We present the ultra-fast dynamics of the interaction between a high-intensity extreme contrast (expected to be around 1e-18 at hundreds of picoseconds timescale) femtosecond laser and a solid. Simultaneous measurements of probe Doppler spectrometry and reflectivity in pump-probe experiments reveal the presence of extreme pressure in the solid density region, which triggers a long-lived (about 15 ps) strong inward shock. Hydrodynamic simulations accurately replicate these observations, providing a detailed explanation of the underlying physics

physics.plasm-ph↗

arXiv2025

Efficient electron heating by laser in finite sized plasma micro-globular targets by repeated collisions of surface and bulk waves

A new mechanism of enhanced laser energy absorption in plasma microglobules is demonstrated with the help of two-dimensional Particle-In-Cell (PIC) simulations. The mechanism relies on the excitation of surface and bulk waves and the occurrence of repeated collisions in the confines of the finite-sized microglobular target. The episodic increase in the average particle energy correlates with the repeated collision of the surface and bulk waves that get excited by the laser on the target. It is shown that the size of the microglobular target governs the efficiency of absorption and the timings of episodic events of energy enhancement. This study thereby illustrates the novel efficient possibility that a closed plasma target provides for energy extraction. Parallels of such colliding waves creating havoc in terms of wave breaking etc. can be witnessed on the ocean surface, seismic disturbances traversing as body waves traverse reflecting and refracting in the interior of the Earth along with surface waves (propagating on the curved surface of the Earth) converge at the antipode to create destruction. Our studies here show the importance of choosing closed targets which aid in the process of repeated energy transfer to particles and often their thermalization. The waves keep propagating in the closed confines rather than getting dissipated over an extended region as would happen for extended targets.

physics.plasm-ph↗

arXiv2023

Mapping the complete evolution of magnetic excitation in beam-plasma system driven by an ultra-intense, femtosecond laser

Plasmas are beset with instabilities of all types, hydrodynamic, magneto-hydrodynamic, and electromagnetic. These instabilities are complex, occur over a large range of temporal and spatial scales, are most often unmanageable, and have seriously challenged our efforts at applications, even as they have shed light on the understanding of the physics of plasmas in the laboratory and astrophysical environments. A major reason for our limited success in their containment is the lack of direct experimental information on their origins and evolution, both temporal and spatial. In plasmas produced by high-intensity, short, and ultrashort pulse lasers, our knowledge of the instability stems from the (secondary) signals they generate e.g. scattering of electromagnetic waves in the form of Raman or Brillouin scattering. Rarely, if ever, has a direct measurement been made of the instantaneous evolution of the instabilities in plasmas. In this paper, we present direct measurements of the femtosecond evolution of the electromagnetic beam-driven instability that arises from the interaction of forward and return currents in an ultrahigh-intensity laser-produced plasma on a solid target.

physics.plasm-ph↗