title: Quasi-phase matching of high-order harmonic generation at high photon energies using counterpropagating pulses.
abstract: We extend all-optical quasi-phase matching of high-order harmonic generation into spectral regions where conventional phase matching is not possible. The high laser intensities required to generate harmonics at energy >130 eV, coupled with the resulting high level of ionization, preclude conventional phase matching in all nonlinear media. Selective enhancement factors between 40 and 150 in the flux of harmonics at photon energies around 140 eV are demonstrated using a train of two counterpropagating pulses.
authors.affiliation: JILA and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA. lytle@colorado.edu
authors.forename: A L
authors.initials: AL
authors.lastname: Lytle
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: P
authors.initials: P
authors.lastname: Arpin
authors.forename: O
authors.initials: O
authors.lastname: Cohen
authors.forename: M M
authors.initials: MM
authors.lastname: Murnane
authors.forename: H C
authors.initials: HC
authors.lastname: Kapteyn