A Versatile Setup for Ultrafast Broadband Optical Spectroscopy of Coherent Collective Modes in Strongly Correlated Quantum Systems

TL;DR

This paper presents a versatile femtosecond pump-probe setup optimized for broadband transient reflectivity experiments, enabling detailed studies of coherent modes in strongly correlated quantum materials across a wide temperature range.

Contribution

The authors develop a broadband, high-resolution optical spectroscopy setup with single-shot CMOS detection, capable of resolving ultrafast coherent oscillations in strongly correlated systems.

Findings

Resolved coherent optical phonons in La$_2$CuO$_4$ up to 13 THz

Achieved temporal resolution of 45 fs and broad spectral detection from 1.75 to 2.85 eV

Demonstrated high frame rate detection at 10 kHz for ultrafast measurements

Abstract

A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide range of temperatures. By combining a temporal resolution of 45 fs and a broad detection range between 1.75 and 2.85 eV, this apparatus can provide insightful information on the interplay between coherent collective modes and high-energy electronic excitations, which is one of the distinctive characteristics of strongly interacting and correlated quantum systems. The use of a single-shot readout CMOS array detector at frame rates up to 10 kHz allows to resolve coherent oscillations with amplitudes below 10$^{-4}$ in $\Delta$R/R. We demonstrate the operation of this setup on the prototypical charge-transfer insulator La$_2$CuO$_4$, revealing the presence of coherent optical phonons with frequencies as high as 13 THz.