Probing of a surface plasma wave by an obliquely incident laser on the metal surface

A surface plasma wave (SPW) of frequency omega(1) and wave number k(1) propagating along a metal-free space boundary exerts a ponderomotive force on the free electrons, creating an electron density perturbation at frequency 2 omega(1). When a laser of frequency omega(2) and wave number k(2) is incident at a suitable angle on the metal surface, it gives rise to the oscillatory velocity of electrons at frequency omega(2). This oscillatory velocity couples with the density perturbation to generate a nonlinear current at frequency 2 omega(1)+omega(2). The nonlinear current derives a radiating wave under suitable conditions. By measuring the amplitude of the radiating wave, the SPW field can be probed.