Laser harmonic generation from a thin metallic foil

A high-power p-polarized laser, obliquely incident on a thin metal foil (i.e., an overdense plasma), induces periodic charge on the surface by emitting electrons into vacuum during a quarter cycle. The electrons are pulled out by the normal component of laser field. As these electrons travel in vacuum, they see the laser field, as well as a direct current field due to surface charge, giving rise to strong anharmonicity in orbits. These anharmonic oscillating dipoles produce coherent radiation at several harmonics. The power of harmonics goes as square of laser spot size and square of pump power for all the harmonics. It scales as sin⁶ θ_i with the angle of incidence θ_i. However, it decreases with harmonic number.