Universal properties of locally generated terahertz waveforms from polarization-controlled two- and multi-color ionizing fields

TL;DR

This paper investigates the polarization properties of terahertz radiation generated in a gas by strong multi-frequency fields, revealing a universal linear increase in ellipticity with frequency and demonstrating control over polarization states.

Contribution

It uncovers a universal linear chirp of ellipticity in THz waveforms from plasma sources and provides a general expression for their polarization control.

Findings

Ellipticity of THz waveforms increases linearly with frequency.

Polarization states can be manipulated via pump pulse polarization.

The linear chirp is a unique property of plasma-based THz generation.

Abstract

The polarization states of terahertz (THz) radiation generated in a photo-ionized gas driven by strong two- or multi-frequency fields with locally controlled polarization are studied. We reveal a universal property of the resulting THz waveforms: the ellipticity of their polarization state increases linearly with the frequency. This ``linear chirp of ellipticity'' makes plasma-based THz generation unique among other THz sources. However, it also puts some constraints on the polarization properties of the generated THz radiation. We derive a general expression for the THz ellipticity and demonstrate how the polarization states of the generated THz waveforms can be manipulated and controlled by the polarization of the pump pulses.