Study of the skin depth and electromagnetic field evolution in laser-generated plasma with different density profiles

Electromagnetic waves absorption in plasma is primarily influenced by the electron density and the plasma's thickness. The oscillating electric field accelerates electrons, and then collides with neutral particles, dissipating energy. A thinner plasma layer results in fewer collisions, allowing more wave energy to pass through and potentially increasing energy absorption downstream. This paper presents a comprehensive study, using the classical Drude model, of skin depth and power absorption in plasmas with various electron density profiles under laser irradiation. The presence of a density gradient significantly affects laser absorption by shifting the resonance region, thus playing a crucial role in laser-plasma interactions. The behavior of skin depth and absorbed power is analyzed as functions of key plasma parameters, including electron density and collision frequency. Results indicate that reducing the plasma thickness enhances the maximum absorbed power. Additionally, this study examines the evolution of electric and magnetic fields during high-power laser interaction with inhomogeneous plasmas exhibiting linear and Epstein density profiles. Unlike the vacuum case, where electric and magnetic fields remain in phase (zero-phase difference), the phase relationship becomes spatially variable within the plasma. The negative gradient of the square of the electric field generates nonlinear forces that drive plasma ablation, expelling material outward toward the vacuum, while simultaneously compressing the plasma interior.