Terahertz emission from metal nanoparticles due to ultrafast heating

TL;DR

This paper theoretically demonstrates that ultrafast heating of metal nanoparticles by femtosecond laser pulses can generate coherent terahertz radiation through temperature gradient-induced polarization, with controllable waveforms based on nanoparticle geometry.

Contribution

It introduces a new mechanism for THz generation from metal nanoparticles driven by ultrafast heating and temperature gradients, explaining recent experimental observations.

Findings

Ultrafast heating induces low-frequency polarization in nanoparticles.

THz waveforms can be controlled by nanoparticle geometry.

The mechanism explains recent experimental THz emissions from nanostructures.

Abstract

We demonstrate theoretically that ultrafast heating of metal nanoparticles by the laser pulse should lead to the generation of coherent terahertz (THz) radiation during the heat redistribution process. It is shown that after the femtosecond laser pulse action the time-dependent gradient of the electronic temperature induces low-frequency particle polarization with the characteristic timescale of about fractions of picosecond. In the case of the directed metallic pattern, the THz pulse waveform can be controlled by changing geometry of the individual particle. The generation mechanism proposed in this Letter can be used for interpretation of the recent experiments on the THz generation from metallic nanoparticles and nanostructures.