Electron parametric instabilities in nonuniform plasma with a strong density gradient excited by femtosecond laser pulses of subrelativistic intensity

We consider the excitation of electron parametric instability in the oblique incidence of femtosecond laser radiation of subrelativistic intensity on a plasma with the nonuniformity scale length of the order of the radiation wavelength λ. Estimates are obtained for two-plasmon instability increments in this plasma, and the generation of plasma waves due to parametric instabilities is numerically simulated by the particle-in-cell technique. The spatial spectrum of these waves is shown to broaden to the level corresponding to several values of the wavenumber k₀ of the component aligned with the electron density gradient and the wavenumbers of the component normal to the gradient have values ~k₀.