Effect of self-focusing on laser third harmonic generation in a clustered gas

An intense Gaussian laser beam propagating through a gas embedded with atomic clusters creates a nanoplasma medium which supports self focusing of the laser beam. The laser beam produces a third harmonic due to nonlinear electron response. The efficiency of the process is sensitive to the focusing of the fundamental laser beam. The harmonic generation yield increases as the clusters expand under hydrodynamic pressure and attains a maximum at the instant when plasma density inside clusters equals three times the critical density. Further, the self-focusing of the laser enhances the efficiency of harmonic generation by ten times.