title: Terahertz-pulse generation by photoionization of air with laser pulses composed of both fundamental and second-harmonic waves.
abstract: Intense radiation in the terahertz (THz) frequency range can be generated by focusing of an ultrashort laser pulse composed of both a fundamental wave and its second-harmonic field into air, as reported previously by Cook et al. [Opt. Lett. 25, 1210 (2000)]. We identify a threshold for THz generation that proves that generation of a plasma is required and that the nonlinearity of air is insufficient to explain our measurements. An additional THz field component generated in the type I beta-barium borate crystal used for second-harmonic generation has to be considered if one is to avoid misinterpretation of this kind of experiment. We conclude with a comparison that shows that the plasma emitter is competitive with other state-of-the-art THz emitters.
authors.affiliation: Physikalisches Institut der Johann Wolfgang Goethe-Universität Frankfurt am Main, Robert-Mayer-Strasse 2-4, D-60054 Frankfurt am Main, Germany. m.kress@physik.uni-frankfurt.de
authors.forename: Markus
authors.initials: M
authors.lastname: Kress
authors.forename: Torsten
authors.initials: T
authors.lastname: Löffler
authors.forename: Susanne
authors.initials: S
authors.lastname: Eden
authors.forename: Mark
authors.initials: M
authors.lastname: Thomson
authors.forename: Hartmut G
authors.initials: HG
authors.lastname: Roskos