Quasi-phase matching of high-order harmonic generation at high photon energies using counterpropagating pulses

摘要

We extend all-optical quasi-phase matching of high-order harmonic generation into spectral regions wherenconventional phase matching is not possible. The high laser intensities required to generate harmonics atnenergy u0001130 eV, coupled with the resulting high level of ionization, preclude conventional phase matchingnin all nonlinear media. Selective enhancement factors between 40 and 150 in the flux of harmonics at photonnenergies around 140 eV are demonstrated using a train of two counterpropagating pulses. © 2008 OpticalnSociety of America