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

A surface plasma wave (SPW) of frequency ω1 and wave number k1 propagating along a metal-free space boundary exerts a ponderomotive force on the free electrons, creating an electron density perturbation at frequency 2 ω1. When a laser of frequency ω2 and wave number k2 is incident at a suitable angle on the metal surface, it gives rise to the oscillatory velocity of electrons at frequency ω2. This oscillatory velocity couples with the density perturbation to generate a nonlinear current at frequency 2 ω1 + ω2. The nonlinear current derives a radiating wave under suitable conditions. By measuring the amplitude of the radiating wave, the SPW field can be probed.