title: CEP-stable tunable THz-emission originating from laser-waveform-controlled sub-cycle plasma-electron bursts.
abstract: We study THz-emission from a plasma driven by an incommensurate-frequency two-colour laser field. A semi-classical transient electron current model is derived from a fully quantum-mechanical description of the emission process in terms of sub-cycle field-ionization followed by continuum-continuum electron transitions. For the experiment, a CEP-locked laser and a near-degenerate optical parametric amplifier are used to produce two-colour pulses that consist of the fundamental and its near-half frequency. By choosing two incommensurate frequencies, the frequency of the CEP-stable THz-emission can be continuously tuned into the mid-IR range. This measured frequency dependence of the THz-emission is found to be consistent with the semi-classical transient electron current model, similar to the Brunel mechanism of harmonic generation.
authors.forename: T
authors.initials: T
authors.lastname: Balčiūnas
authors.forename: D
authors.initials: D
authors.lastname: Lorenc
authors.forename: M
authors.initials: M
authors.lastname: Ivanov
authors.forename: O
authors.initials: O
authors.lastname: Smirnova
authors.forename: A M
authors.initials: AM
authors.lastname: Zheltikov
authors.forename: D
authors.initials: D
authors.lastname: Dietze
authors.forename: K
authors.initials: K
authors.lastname: Unterrainer
authors.forename: T
authors.initials: T
authors.lastname: Rathje
authors.forename: G G
authors.initials: GG
authors.lastname: Paulus
authors.forename: A
authors.initials: A
authors.lastname: Baltuška
authors.forename: S
authors.initials: S
authors.lastname: Haessler