Quantitative time-resolved buildup in coherent anti-Stokes Raman scattering

TL;DR

This paper demonstrates how to control and measure the gradual buildup of the CARS signal using laser pulse shaping, providing insights into its dynamics and potential for species-specific sensing.

Contribution

It introduces a time-resolved CARS technique with shaped laser pulses to control and observe signal buildup, advancing quantitative understanding of CARS processes.

Findings

CARS signal buildup can be delayed with pulse shaping.

Resonant CARS buildup is tunable by probe pulse width.

Off-resonant water molecules do not show buildup delay.

Abstract

Since its first demonstration in the sixties, coherent anti-Stokes Raman scattering (CARS) has become a powerful spectroscopic sensing tool with broad applications in biology and chemistry. However, it is a complex nonlinear optical process that often leads to the lacks of quantitative data outputs. In this letter, we observe how CARS signal builds up gradually and demonstrate how to control its deferral with laser-pulse shaping. A time-resolved three-color CARS that involves a pair of driving broadband femtosecond pulses and delayed shaped probe pulse is realized experimentally. Driving pulses are tuned to the Raman-resonance onto the vibrational ring modes of pyridine and benzene molecules. As a result, CARS-buildup is deferred in picoseconds as delayed probe pulse width varies from 50 down to 10 cm-1. With off-resonant driving of water molecules this effect, in contrary, does not occur. Laser control predicting deferred resonant processes can serve as a novel and important species-specific indicator in, e.g., machine learning applications for future nonlinear optical spectroscopy.