Attosecond transient grating spectroscopy with near-infrared grating pulses and an extreme ultraviolet diffracted probe

TL;DR

This paper introduces attosecond transient grating spectroscopy using high-harmonic XUV pulses and NIR pulses to study ultrafast dynamics in materials, offering element-specific insights at unprecedented timescales.

Contribution

It develops a novel attosecond transient grating spectroscopy technique combining XUV and NIR pulses, enabling element-specific, background-free measurements of ultrafast carrier and lattice dynamics.

Findings

Observed coherent phonon generation in Sb thin films

Measured carrier thermalization and cooling timescales

Extracted complex dielectric constant during dynamics

Abstract

Transient grating spectroscopy has become a mainstay among metal and semiconductor characterization techniques. Here we extend the technique towards the shortest achievable timescales by using tabletop high-harmonic generation of attosecond extreme ultraviolet (XUV) pulses that diffract from transient gratings generated with 500-1000 nm sub-5 fs near-infrared (NIR) pulses. We demonstrate the power of attosecond transient grating spectroscopy (ATGS) by investigating the ultrafast photoexcited dynamics in an Sb semimetal thin film. ATGS provides an element-specific, background-free signal, unfettered by spectral congestion, in contrast to transient absorption spectroscopy. With the ATGS measurements in Sb polycrystalline thin films, we observe the generation of coherent phonons and investigate the lattice and carrier dynamics. Among the latter processes, we extract carrier thermalization, hot carrier cooling, and electron-hole recombination, which are on the order of 20 fs, 50 fs, and 2 ps, timescales, respectively. Furthermore, simultaneous collection of transient absorption and transient grating data allows us to extract the total complex dielectric constant in the sample dynamics, including the real-valued refractive index, from which we are also able to investigate carrier-phonon interactions and longer-lived phonon dynamics. The outlined experimental technique expands the capabilities of transient grating spectroscopy and attosecond spectroscopies by providing a wealth of information concerning carrier and lattice dynamics with an element-selective technique, at the shortest achievable timescales.