title: Probe of high-order harmonic generation in a hollow waveguide geometry using counterpropagating light.
abstract: We use counterpropagating light to directly observe the coherent buildup of high harmonic generation in a hollow waveguide geometry. We measure, for the first time, coherence lengths for high photon energies that cannot be phase matched using conventional approaches. We also probe the transition through phase matching, the ionization level at which different harmonic orders are generated, and the change in the coherence length as the driving laser is depleted. These results directly prescribe the optimal structures or pulse trains required for implementing quasiphase matching.
authors.affiliation: JILA and Department of Physics University of Colorado at Boulder, 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: J
authors.initials: J
authors.lastname: Peatross
authors.forename: M M
authors.initials: MM
authors.lastname: Murnane
authors.forename: H C
authors.initials: HC
authors.lastname: Kapteyn
authors.forename: O
authors.initials: O
authors.lastname: Cohen