title: Evidence for third-harmonic generation in disguise of second-harmonic generation in extreme nonlinear optics.
abstract: In contrast with traditional nonlinear optics, a peak at the spectral position of the second harmonic of a laser can also be generated in an inversion-symmetric medium in the regime of extreme nonlinear optics. We describe the underlying mechanism of such third-harmonic generation in disguise of second-harmonic generation and compare theory with the optical as well as the radio-frequency spectra measured in recent experiments on thin ZnO films. The peak at twice the carrier-envelope offset frequency in the radio-frequency spectra is shown to be an unambiguous signature of such a process.
authors.affiliation: Institut für Angewandte Physik, Universität Karlsruhe (TH), Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Tritschler
authors.forename: O D
authors.initials: OD
authors.lastname: Mücke
authors.forename: M
authors.initials: M
authors.lastname: Wegener
authors.forename: U
authors.initials: U
authors.lastname: Morgner
authors.forename: F X
authors.initials: FX
authors.lastname: Kärtner