A tunable time-resolved spontaneous Raman spectroscopy setup for probing ultrafast collective excitation and quasiparticle dynamics in quantum materials

TL;DR

This paper introduces a versatile ultrafast time-resolved Raman spectroscopy setup capable of probing collective excitations and quasiparticle dynamics in quantum materials with broad tunability and high efficiency.

Contribution

The authors develop a flexible, high-efficiency Raman spectroscopy system with tunable energy and time resolution, enabling detailed study of ultrafast dynamics in quantum materials.

Findings

Demonstrated phonon and hole dynamics in silicon.

Detected unequal phonon softening at different Brillouin zone points.

Observed magnon softening and broadening in Cu2OSeO3.

Abstract

We present a flexible and efficient ultrafast time-resolved spontaneous Raman spectroscopy setup to study collective excitation and quasi-particle dynamics in quantum matter. The setup has a broad energy tuning range extending from the visible to near infrared spectral regions for both the pump excitation and Raman probe pulses. Additionally, the balance between energy and time-resolution can be controlled. A high light collecting efficiency is realized by high numerical aperture collection optics and a high-throughput flexible spectrometer. We demonstrate the functionality of the setup with a study of the zone-center longitudinal optical phonon and hole continuum dynamics in silicon, and discuss the role of the Raman tensor in time-resolved Raman scattering. In addition, we show evidence for unequal phonon softening rates at different high symmetry points in the Brillouin zone of silicon by means of detecting pump-induced changes in the two-phonon overtone spectrum. Demagnetization dynamics in the helimagnet Cu2OSeO3 is studied by observing softening and broadening of a magnon after photo-excitation, underlining the unique power of measuring transient dynamics in the frequency domain, and the feasibility to study phase transitions in quantum matter.