Terahertz frequency conversion at plasma-induced time boundary

TL;DR

This paper demonstrates how ultrafast plasma-induced time boundaries can be used to achieve broadband frequency conversion of terahertz waves, offering new avenues for spectral engineering and temporal control in THz photonics.

Contribution

It introduces a novel method of terahertz frequency conversion using femtosecond laser-induced plasma time boundaries, combining experimental and theoretical insights.

Findings

Red and blue shifts observed across broadband THz spectrum

Temporal boundaries outperform spatial boundaries in spectral manipulation

Potential for applications in THz technology and photonic time crystals

Abstract

We report on the frequency conversions of terahertz (THz) waves at ultrafast time boundaries created via femtosecond laser-induced air-to-plasma phase transitions. Our combined experimental and theoretical approach reveals that the abrupt change in refractive index at the ultrafast time boundaries drives both the red and blue shifts over the broadband THz spectrum due to the dispersive plasma, with distinctive amplitude variations. The present study contrasts these effects with those from spatial boundaries, highlighting the superior efficacy of temporal manipulations for spectral engineering. These findings not only deepen the understanding of light-matter interactions in time-varying media but also pave the way for innovative applications in THz technology and lay the groundwork for the observation of temporal reflection effects, photonic time crystals, and spatio-temporally modulated matter.