Effects of external static magnetic field (applied in $\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser $({\rm \omega} _0,\;\vec k_{0z})$ is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0 driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW $({\rm \omega}, \;\vec k_z)$ and produces nonlinear current to drive another counter propagating SPW $({\rm \omega} _1,\;\vec k_{1z})$ at the phase matching conditions of frequency ω = ω1 − 2ω0 and wavenumber $\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$ (by feedback mechanism). The parametric process becomes resonant at 2ω0 ≈ ωp and the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

A high-frequency surface plasma wave (SPW) excited over metallic surface irradiated by a laser beam, can undergo stimulated Compton scattering if phase velocity of daughter plasma wave is equal to the Fermi velocity for metal. The pump SPW ${\rm (}{{\rm \omega} _0},{\vec k_{0{\rm z}}})$ parametrically excites a quasi-electrostatic plasma wave ${\rm (\omega}, {\vec k_{\rm z}})$ and a backscattered sideband SPW ${\rm (}{{\rm \omega} _1},{\vec k_{1{\rm z}}})$ at resonance ω0 = ω − ω1 and ${\vec k_{0{\rm z}}} = {\vec k_{\rm z}} - {\vec k_{1{\rm z}}}$. The growth rate of Compton process increases with the frequency of incident laser and turns out to be 5.425 × 1010 rad/s at laser frequency ω0 = 0.7595 × 1015 rad/s for incident laser amplitude A0L = 11 × 1011 V/m, laser spot size b = 1.38 × 10−5 m, and free electron density of metal n0 = 5.85 × 1028/m3. The excitation of highly damped quasi-electrostatic plasma wave in this parametric process provide a better nonlinear option for surface heating as compared with direct laser heating. The process can also be used for diagnostics purposes.