Ultrasensitive Doppler Raman spectroscopy using radio frequency phase shift detection

TL;DR

This paper presents a novel radio frequency Doppler Raman spectroscopy method that amplifies weak Raman signals by converting spectral shifts into phase changes in RF signals, enabling detection of signals previously obscured by laser damage limits.

Contribution

The paper introduces the first optical amplification technique for coherent Raman spectroscopy using RF phase shift detection, significantly enhancing sensitivity.

Findings

Enables detection of weaker Raman signals

Amplifies signals by converting spectral shifts to RF phase changes

Potential to observe signals limited by laser damage constraints

Abstract

We introduce the first method to enable an optical amplification of a coherent Raman spectroscopy signal called radio frequency Doppler Raman spectroscopy. Doppler Raman measurements amplify the optical signals in coherent Raman spectroscopy by converting a spectral frequency shift imparted by an impulsive coherent Raman excitation to a change in a probe pulse transit time. This transit time perturbation is detected through the phase of a radio frequency electronic signal measured at a harmonic of the probe pulse train. By exploiting this new capability to scale the signal of a coherent Raman spectroscopic signal, we open the potential to detect very weak Raman spectroscopy signals that are currently not observable due to limits of illumination intensity imposed by laser damage to the specimen.