Noise in stimulated Raman scattering measurement: From basics to practice

TL;DR

This paper reviews laser intensity noise in stimulated Raman scattering (SRS), providing practical tools and models for assessing noise and detection limits in SRS microscopy, with experimental validation on commercial lasers.

Contribution

It offers a comprehensive tutorial with models, measurement methods, and analysis tools for laser noise in SRS, enhancing understanding and performance assessment.

Findings

Derived PSD, RIN, SNR, and sensitivity expressions for SRS systems.

Presented two methods for measuring RIN and system performance.

Validated noise assessment techniques on commercial lasers.

Abstract

We revisit laser intensity noise in the context of stimulated Raman scattering (SRS), which has recently proved to be a key technique to provide label free images of chemical bonds in biological and medical samples. Contrary to most microscopy techniques, which detect a weak photon flux resulting from light matter interactions, SRS is a pump-probe scheme that works in the high flux regime and happens as a weak modulation ($10^{-4}-10^{-6}$) in a strong laser field. As a result, laser noise is a key issue in SRS detection. This practical tutorial provides the experimentalists with the tools required to assess the amount of noise and the ultimate SRS detection limit in a conventional lock-in-based SRS system. We first define the quantities that are relevant when discussing intensity noise, and illustrate them through a conventional model of light detection by a photodiode. Stimulated Raman Scattering is then introduced in its lock-in-based implementation, and the model presented is adapted in this particular case. The power spectral density (PSD), relative intensity noise (RIN), signal to noise ratio (SNR), and sensitivity of the system are derived and discussed. Two complementary methods are presented that allow measurement of the RIN and assessment of the performance of a SRS system. Such measurements are illustrated on two commercial laser systems. Finally, the consequences of noise in SRS are discussed, and future developments are suggested. The presentation is made simple enough for under-graduated, graduated students, and newcomers in the field of stimulated Raman, and more generally in pump-probe based schemes.