title: Spatial properties of odd and even low order harmonics generated in gas.
abstract: High harmonic generation in gases is developing rapidly as a soft X-ray femtosecond light-source for applications. This requires control over all the harmonics characteristics and in particular, spatial properties have to be kept very good. In previous literature, measurements have always included several harmonics contrary to applications, especially spectroscopic applications, which usually require a single harmonic. To fill this gap, we present here for the first time a detailed study of completely isolated harmonics. The contribution of the surrounding harmonics has been totally suppressed using interferential filtering which is available for low harmonic orders. In addition, this allows to clearly identify behaviors of standard odd orders from even orders obtained by frequency-mixing of a fundamental laser and of its second harmonic. Comparisons of the spatial intensity profiles, of the spatial coherence and of the wavefront aberration level of 5ω at 160 nm and 6ω at 135 nm have then been performed. We have established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6ω spatial intensity distribution. This undesirable effect can be easily controlled. We finally conclude that the spatial quality of an even harmonic can be as excellent as in standard generation.
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: G
authors.initials: G
authors.lastname: Lambert
authors.affiliation: Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, 1, build.2, 119991, Moscow, Russia.
authors.forename: A
authors.initials: A
authors.lastname: Andreev
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: J
authors.initials: J
authors.lastname: Gautier
authors.affiliation: Unità Tecnica Sviluppo di Applicazioni della Radiazione - Modellistica Matematica, ENEA Centro Ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Giannessi
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: V
authors.initials: V
authors.lastname: Malka
authors.affiliation: Unità Tecnica Sviluppo di Applicazioni della Radiazione - Modellistica Matematica, ENEA Centro Ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Petralia
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: S
authors.initials: S
authors.lastname: Sebban
authors.affiliation: 1] Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory, 1, build.2, 119991, Moscow, Russia [2] National Research Centre "Kurchatov Institute", pl. Akademika Kurchatova, 1, Moscow, 123182 Russia.
authors.forename: S
authors.initials: S
authors.lastname: Stremoukhov
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: F
authors.initials: F
authors.lastname: Tissandier
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: B
authors.initials: B
authors.lastname: Vodungbo
authors.affiliation: Laboratoire d'Optique Appliquée, UMR 7639, ENSTA-CNRS-École Polytechnique, Chemin de la Hunière, 91761 Palaiseau, France.
authors.forename: Ph
authors.initials: P
authors.lastname: Zeitoun