Phase matching and harmonic generation in Bessel Gauss–beams

Conversion efficiencies and far-field profiles for third-order harmonic generation in an atomic medium irradiated by an intense Bessel–Gauss beam are calculated with an integral method. The calculation takes into account the nonperturbative variation of the atomic polarizabilities, target depletion by photoionization, and the effect of the free electrons. Numerical results are presented for a pump beam of 355-nm wavelength and up to 3×1013 W/cm2 intensity incident on hydrogen. They are compared with equivalent results for a pure Gaussian pump beam. Significant differences are found that originate from the different phase-matching properties and intensity profile of Bessel–Gauss beams.