[论文解读] Noise in stimulated Raman scattering measurement: From basics to practice

Xavier Audier, Sandro Heuke+3 more|arXiv (Cornell University)|Oct 28, 2019

Spectroscopy Techniques in Biomedical and Chemical Research参考文献 37被引用 77

一句话总结

本论文提供一个实用教程，用以表征 SRS 系统中的激光强度噪声，推导噪声如何限制 SRS 检测，并提供用基于锁相的 SRS 的噪声测量与优化 RIN 的实验方法。它将理论噪声模型与使用商用激光器的实际测量联系起来。

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.

研究动机与目标

• 定义光强检测中的关键噪声量，并将其与 SRS 检测极限联系起来。
• 将常规光电二极管噪声模型适配为基于锁相的 SRS 设置。
• 推导与 SRS 相关的 PSD、RIN、SNR 和系统灵敏度表达式。
• 提出并在两种互补的商业激光器上演示两种 RIN 测量方法。
• 提供切实可行的建议以最大化 SNR，并讨论未来的噪声降低方向。

提出的方法

• 给出带脉冲激光的光电探测的标准半经典模型。
• 在噪声源作用下推导探测器电流的 PSD、RIN 和 SNR 表达式。
• 将该模型适配为带幅度调制和解调的基于锁相的 SRS。
• 以 RIN 和系统参数表示推导 SNR 与最小可检测的 SRS 增益 beta_min。
• 描述在商业激光器上测量激光 RIN 的两种实验方法。
• 用两种商业激光系统的测量结果来说明这些方法。

实验结果

研究问题

• RQ1 在锁相系统中，激光强度噪声（电子噪声、散粒噪声及过剩噪声）如何限制 SRS 检测？
• RQ2 如何测量并最小化 RIN 以优化 SRS 的 SNR 与灵敏度？
• RQ3 调制频率、锁相带宽与 SRS 检测极限之间的关系是什么？
• RQ4 不同的激光源在实际中如何影响 RIN 与 SRS 性能？

主要发现

• 基于锁相的 SRS 系统中的 SNR 与在锁相带宽上积分的激光 RIN 成反比。
• SRS 灵敏度 beta_min 与锁相带宽与 RIN 的乘积的平方根成正比。
• 锁相检波将低频激光噪声迁移到调制频率，通过适当选择 f0 实现更高的 SNR。
• 两种实验性 RIN 测量方法可在频率和强度范围内表征 RIN 面。
• 在两套商业激光系统上测得的激光 RIN 在较高频率下与一个设备的散粒噪声极限一致，验证了该模型在实践中的有效性。
• 提供了一个明确的框架，通过平衡调制频率、带宽和平均探测电流来优化 SRS 性能。