Harmonic generation in gases by use of Bessel-Gauss laser beams

We have experimentally investigated the use of diffraction-free beams to ge nerate low-order harmonics in gas jets. Bessel-Gauss beams have been genera ted from a Ti:sapphire, 100-fs laser by use of annular apertures and then b y focusing of the ring-type-produced radiation. The conversion efficiencies for these beams for the third- and fifth-order harmonic generation in xeno n have been measured and compared with those of pure Gaussian beams of the same energy content. We have thus found that, by matching the gas medium le ngth to the range of the Bessel-Gauss beams, conversion efficiencies consid erably higher than those of Gaussian beams can be obtained. The experimenta l results have also been discussed and interpreted in terms of a simple num erical model that emphasizes the effects of phase matching in the two diffe rent geometries. (C) 2000 Optical Society of America [S0740-3224(00)01001-8 ] OCIS codes: 190.4160, 190.4180, 020.4180.