Parametric excitation of surface plasma waves over a metallic surface by laser in an external magnetic held

摘要

Effects of external static magnetic field (applied in gamma-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser (omega(0), (k)over-right-arrow(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 2 omega(0). The electron density perturbation at frequency 2 omega(0) driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW (omega, (k)over-right-arrow(z)) and produces nonlinear current to drive another counter propagating SPW (omega(1), (k)over-right-arrow(1z)) at the phase matching conditions of frequency omega = omega(1) - 2 omega(0) and wavenumber (k)over-right-arrow(z) = (k)over-right-arrow(1z) - (k)over-right-arrow(0z), (by feedback mechanism). The parametric process becomes resonant at 2 omega(0) approximate to omega(p) and the maximum growth rate is achieved for an incidence angle of laser theta = 40 degrees. 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.