Diffractionless beams and their use for harmonic generation

Use of diffraction-free beams to generate low-order harmonies in xenon jets has been investigated. Nearly diffractionless beams have been generated from a Ti: sapphire, 100 fs, laser system by focussing ring-type radiation. which has been produced in two different ways: either, by inserting an annular slit into the incident Gaussian beam, or by placing a doublet of axicons in a vertex-to-vertex configuration before the focussing lens. The results obtained with the first scheme are discussed and interpreted in terms of a simple perturbative model of the harmonic generation (HG) process. The first measurements performed with the doublet of axicons are also reported and discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.