title: Extended phase matching of high harmonics driven by mid-infrared light.
abstract: We demonstrate that phase-matched frequency upconversion of ultrafast laser light can be extended to shorter wavelengths by using longer driving laser wavelengths. Experimentally, we show that the phase-matching cutoff for harmonic generation in argon increases from 45 to 100 eV when the driving laser wavelength is increased from 0.8 to 1.3 microm. Phase matching is also obtained at higher pressures using a longer-wavelength driving laser, mitigating the unfavorable scaling of the single-atom response. Theoretical calculations suggest that phase-matched high harmonic frequency upconversion driven by mid-infrared pulses could be extended to extremely high photon energies.
authors.affiliation: JILA, University of Colorado at Boulder and National Institute of Standards and Technology, Boulder, CO 80309, USA. popmintchev@jila.colorado.edu
authors.forename: Tenio
authors.initials: T
authors.lastname: Popmintchev
authors.forename: Ming-Chang
authors.initials: MC
authors.lastname: Chen
authors.forename: Oren
authors.initials: O
authors.lastname: Cohen
authors.forename: Michael E
authors.initials: ME
authors.lastname: Grisham
authors.forename: Jorge J
authors.initials: JJ
authors.lastname: Rocca
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kapteyn