Laser third-harmonic generation in clustered plasmas

An intense short pulse laser propagating through a gas jet comprised of clusters, quickly converts the clusters into plasma balls and causes oscillations of the electron cloud in the direction of the electric field of the laser. In each wave period, electrons spend a significant amount of their time outside the clusters, leaving behind a net positive charge and the clusters undergo Coulomb explosion and expand. During the expansion when the cluster electrons plasma frequency equals times the laser frequency, , the electron quiver velocity is resonantly enhanced. The nonlinear electron response gives rise to the generation of a third-harmonic. At a typical laser intensity of I L ≈ 10 15 W cm −2 at 1 μm wavelength, the normalized third-harmonic amplitude of the pump wave in a deuterium cluster of radius 100 Å, and density ∼10 14 cm −3 , turns out to be 1.7×10 −3 .