Does femtosecond time-resolved second-harmonic generation probe electron temperatures at surfaces?

TL;DR

This study investigates whether femtosecond time-resolved second-harmonic generation can probe electron temperatures at metal surfaces, revealing that the sensitivity depends on material-specific factors like nonlinear susceptibility and Fresnel effects.

Contribution

It demonstrates that SHG sensitivity to electron temperature varies between materials, highlighting the importance of nonlinear susceptibility and Fresnel factors in surface electron dynamics detection.

Findings

Ag and Au show electron temperature dependence in nonlinear susceptibility.

Cu's electron temperature dependence appears in Fresnel factors.

SHG sensitivity to electron dynamics is material-dependent.

Abstract

Femtosecond pump-probe second-harmonic generation (SHG) and transient linear reflectivity measurements were carried out on polycrystalline Cu, Ag and Au in air to analyze whether the electron temperature affects Fresnel factors or nonlinear susceptibilities, or both. Sensitivity to electron temperatures was attained by using photon energies near the interband transition threshold. We find that the nonlinear susceptibility carries the electron temperature dependence in case of Ag and Au, while for Cu the dependence is in the Fresnel factors. This contrasting behavior emphasizes that SHG is not a priori sensitive to electron dynamics at surfaces or interfaces, notwithstanding its cause.