A. A. Molavi Choobini1*, F. M. Aghamir1, S. S. Ghaffari-Oskooei2.1- Dept. of Physics, University of Tehran, Tehran 14399-55961, Iran,2- Department of Atomic and Molecular Physics, Faculty of Physics, Alzahra University, Tehran, Iran.Abstract: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, consideringvarious spatial profiles and polarization states. This phenomenon involves modification of the temporal andspatial characteristics of the laser pulse due to the presence of the magnetized plasma. The discussionreveals 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 howthey 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 profileimpact on pulse-shaping and plasma channel formation is also discussed. This exploration sheds light onthe intricate interplays and potential pulse-shaping applications in laser-plasma interactions.
Plasma-based compression techniques utilizing plasma gratings or plasma channels offer a means to induce precise phase modulation and achieve compression effects. These techniques leverage the unique properties of plasmas to control the phase of laser pulses, ultimately leading to pulse compression. In the case of plasma gratings, plasma structures are ingeniously engineered to serve as "gratings" for modulating the phase of the incident laser pulse. This modulation relies on the careful tailoring of electron density and plasma frequency within the plasma structure to achieve the desired compression effects. Figure 4 depicts the variations of the magnitude of normalized electric field as a function of normalized z coordinate over plasma length for different electron densities and Gaussian profile. As the figure indicates, electron density variations in the plasma create regions of different refractive indices. The plasma frequency determines the spacing of these regions and influences
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The self-phase modulation (SPM) occurs when the intensity-dependent refractive index induces a frequency shift in different parts of the pulse. By exercising precise control over the electron density within the plasma structure, one can govern the degree of phase modulation, thereby enabling pulse-shaping and compression through constructive interference. In other words, the plasma frequency introduces dispersion which refers to the dependence of a material refractive index on the frequency of the laser pulse. Different frequency components of pulse travel at different speeds due to the dispersion relation and the resulting spatial delays or spatial phase difference between components leading to pulse compression, affecting pulse-shaping.
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The effects of an external magnetic field on pulse compression in laser-plasma interactions are the result of intricate interplays between electromagnetic forces, plasma dynamics, and the characteristics of the laser pulse. In a high-intensity laser pulse interacting with a plasma, the laser can undergo pulse-shaping due to the ponderomotive force. This force can cause electrons to oscillate, forming density variations in the plasma and causing the density profiles and refractive properties of plasma altered, leading to changes in the laser spatial and temporal characteristics. In addition, the Lorentz force acting on charged particles due to the external magnetic field can compress the plasma. Charged particles experience a magnetic force perpendicular to their velocity and the magnetic field direction. This could affect the spectral components of the laser pulse, potentially leading to different compression dynamics. Therefore, an external magnetic field can alter the trajectories of
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Effect of various external magnetic field on the magnitude of the normalized electric field as a function of normalized z coordinate over plasma length for Gaussian profile is depicted in Fig 5. According to the figure, the presence of a static magnetic field in the plasma affects the speed of electrons in the plasma through cyclotron resonance, especially in the elliptically polarized state, and changes the direction of oscillation. This leads to enhanced relativistic nonlinearity near the gyro-resonance, significantly affecting the effective dielectric constant and other propagation parameters of the X-mode, In turn, it has a direct impact on pulse-shaping and compression. Furthermore, the X-mode has the advantage of being
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