Linear absorption of electromagnetic wave injected in a hot plasma is usually associated with non-normal incidence; here, it is shown that absorption can take place at normal incidence as well. By developing a kinetic model based on integral form of dielectric tensor in the presence of static electric field sustaining the density gradient, the mechanism of energy deposition by an injected electromagnetic wave in strongly inhomogeneous plasma is investigated, taking into account the kinetic effects of wave-particle interaction. Two key features of power absorption by plasma particles are explained successfully: (i) For steep-density-gradient plasma, absorption is nonzero and nonresonant in overdense regions for perpendicular as well as oblique injection, thereby heating the plasma due to abrupt change of wave electric field near critical density layer; and (ii) for shallow gradients, resonant absorption takes place at oblique angles due to Landau damping of an electrostatic wave excited near the resonance point. The developed model establishes the conditions for power absorption over a range of density scale lengths with evaluation of self-consistent stochastic heating in a hot plasma.

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• Electromagnetic waves & oscillations
• Evanescent waves
• Laser-plasma interactions
• Plasma waves
• Plasma-particle interactions
• Wave-wave, wave-particle interactions
• Hot dense plasma
• Laboratory plasma
• Fokker-Planck & Vlasov model
• Plasma kinetic theory