CEP-stable Tunable THz-Emission Originating from Laser-Waveform-Controlled Sub-Cycle Plasma-Electron Bursts

TL;DR

This paper demonstrates a method to generate tunable, CEP-stable THz radiation using a two-color laser field with incommensurate frequencies, supported by a semi-classical model explaining the emission process.

Contribution

It introduces a new approach for continuous tuning of CEP-stable THz emission into the mid-IR range using incommensurate two-color laser fields, supported by a quantum-mechanical model.

Findings

THz emission frequency can be continuously tuned into the mid-IR range.

The experimental results align with the semi-classical transient electron current model.

The method achieves CEP-stable, tunable THz emission using incommensurate laser frequencies.

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.