A Langevin analysis of fundamental noise limits in Coherent Anti-Stokes Raman Spectroscopy

TL;DR

This paper presents a Langevin-based theoretical analysis of quantum noise limits in Coherent Anti-Stokes Raman Spectroscopy, providing analytic results across various experimental setups without relying on adiabatic approximations.

Contribution

It introduces a comprehensive Langevin approach to analyze quantum noise in CARS, deriving general expressions applicable to multiple experimental configurations.

Findings

Medium noise is negligible for short interaction times.

Signal efficiency is fundamentally limited by quantum photon noise.

Analytic solutions are obtained without adiabatic assumptions.

Abstract

We use a Langevin approach to analyze the quantum noise in Coherent Anti-Stokes Raman Spectroscopy (CARS) in several experimental scenarios: with continuous wave input fields acting simultaneously and with fast sequential pulsed lasers where one field scatters off the coherence generated by other fields; and for interactions within a cavity and in free space. In all the cases, the signal as well as the quantum noise due to spontaneous decay and decoherence in the medium are shown to be described by the same general expression. Our theory in particular shows that for short interaction times, the medium noise is not important and the efficiency is limited only by the intrinsic quantum nature of the photon. We obtain fully analytic results \emph{without} making an adiabatic approximation, the fluctuations of the medium and the fields are self solved consistently.