Low Frequency Collinear Pre-Resonant Impulsive Stimulated Raman Spectroscopy

TL;DR

This paper extends impulsive stimulated Raman spectroscopy to the pre-electronic resonance regime using a broadband collinear pump-probe scheme, overcoming noise challenges and demonstrating enhanced low-frequency vibrational detection in crystalline samples.

Contribution

It introduces a novel broadband collinear pump-probe method for low-frequency Raman spectroscopy in the pre-resonant regime, addressing noise issues from competing processes.

Findings

Successful reduction of noise from competing two-photon processes

Demonstration of low-frequency vibrational spectra under near-resonant conditions

Observation of spectral modifications due to electronic-vibrational coupling

Abstract

In this work we extend low frequency impulsive stimulated Raman microspectroscopy to the pre-electronic resonance regime. We use a broadband two color collinear pump probe scheme which can be readily extended to imaging. We discuss the difficulties unique to this type of measurements in the form of competing resonant two-photon processes and the means to overcome them. We successfully reduce the noise which arises due to those competing processes by eliminating the detected spectral components which do not contribute to the vibrational signature of the sample though introduce most of the noise. Finally, we demonstrate low-frequency spectroscopy of crystalline samples under near-resonant pumping showing both enhancement and spectral modification due to coupling with the electronic degree of freedom.