Optical second-and third harmonic radiation generation in a laser-produced plasma

The harmonic generation of a laser in gases is strictly dependent on the ionization dynamics. In this work, we study optical second and third harmonic radiation generation of a laser in an ionizing gas incorporating the electron-ion recombination effects. Neutral gas is irradiated by an intense laser field which generates free-electrons by tunnel ionization. If the laser pulse is long enough, the electron-ion recombination effects need to be accounted for laser dynamics in plasmas. The laser is assumed to have intensity near the tunnel ionization threshold so as to get plasma density varying with time, which in turn gives rise to strong second and third harmonic radiation fields. Here we demonstrate enhanced second- and third-harmonic generation in tunnel-ionizing gas by an intense laser pulse incorporating the effect of electron-ion recombination. The results show that the inclusion of electron-ion recombination reduces the laser defocusing and hence enhances the harmonic radiation amplitudes. A systematic numerical analysis has been done to understand the underlined physics.