Non-linear phase-mismatch compensated by focusing for efficient THG in gases

A possibility of removing the limitation imposed by non-linear refraction on the attainable conversion efficiency is considered for third-harmonic generation (THG) in gaseous media. A numerical analysis has shown that by a proper focusing, the THG efficiency can approach values close to unity in spite of a substantially large value of the inhomogeneos non-linear refraction. The dependence of the conversion efficiency and the optimum linear phase-mismatch on the focusing tightness is presented for the steady- state and pulsed regimes. (Author)