[论文解读] Doppler dual-comb coherent Raman spectromicroscopy

Florian M. Schweizer, Hannah Terrasa+1 more|arXiv (Cornell University)|Mar 24, 2026

Spectroscopy Techniques in Biomedical and Chemical Research被引用 0

一句话总结

本文通过单一超宽带激光产生的多普勒效应生成的两个频梳，提出时域相干拉曼光谱学，借助叉相位调制和下换能，实现背景无、快速且高分辨成像。实现了毫秒级获取以及在约8 μm PMMA 球体上约280 nm 的衍射极限分辨率。

ABSTRACT

Chemical imaging enabled by Raman processes is crucial to investigating biological and chemical samples in a label-free manner. Stimulated Raman spectroscopy (SRS) overcomes the key limitation associated with low signal levels in spontaneous Raman spectroscopy, however, at the expense of probing only narrow Raman bands. Time-domain implementation of coherent anti-Stokes Raman spectroscopy (CARS) by dual frequency combs can achieve broad Raman bandwidths; nevertheless, its execution is demanding due to strenuous temporal-synchronization of two independent ultrashort laser sources. Here, we introduce time-domain coherent Raman spectroscopy utilizing two frequency combs generated by the Doppler effect from a single ultra-broadband laser source. In contrast to CARS, in our approach, the interference of impulsively launched vibrations by two broadband frequency combs (τ ~ 6 fs) periodically modulates the Kerr nonlinear response of the medium, leading to cross-phase modulation (XPM) experienced by both the combs. This phase modulation leads to spectral broadening and periodic modulation in the anti-Stokes region of the combs. Down-conversion by a factor of ~ 10-8 in the frequency of the vibrations enabled by the dual-comb approach empowered us to use photon-counting methodology in the anti-Stokes region. This makes our technique extremely versatile, background-free, sensitive and fast (millisecond acquisition times), in probing a range of samples from wide bandgap dielectrics and liquids to individual micro-particles with nondestructive pulse energies (~ 100 pJ) incident on the sample. Owing to the higher-order nonlinearity involved in the XPM process, we achieved ~ 2.5 times improvement in diffraction-limited spatial resolution (~ 280 nm) in ultra-broadband chemical imaging of a ~ 8 μm bead of poly-methyl-methacrylate.

研究动机与目标

• 通过在自发拉曼光谱中实现更宽的拉曼带宽来解决带宽窄的限制。
• 开发基于一束激光源产生的多普勒生成双梳的时域相干拉曼技术。
• 展示基于交叉相位调制的光谱展宽和反斯塔克调制以实现对光子计数探测的灵敏成像。
• 展示快速获取、低脉冲能量以及对从液体到微粒的多样样品的适用性。

提出的方法

• 由单一超宽带激光源（~6 fs 脉冲）通过多普勒效应生成两路频梳。
• 利用瞬时激发的振动引起的交叉相位调制，从而展宽光谱并调制反斯塔克区域。
• 通过~10^-8 的下转换将振动频率降频，以实现反斯塔克区域的光子计数探测。
• 在 XPM 的高阶非线性下实现光谱展宽，以在超宽带成像中获得改进的空间分辨率(~280 nm)。
• 以对样品无损的脉冲能量 (~100 pJ) 进行成像。
• 提供背景无、快速成像，毫秒级获取时间。

实验结果

研究问题

• RQ1 双梳方案（由多普勒产生）是否能实现带宽宽广且背景无的相干拉曼光谱？
• RQ2 在基于 XPM 的拉曼光谱显微中，空间分辨率与灵敏度的极限是什么？
• RQ3 振动频率的下转换将如何影响探测策略（光子计数）及噪声性能？
• RQ4 该方法是否可广泛应用于固体、液体和微粒，且脉冲能量较低？

主要发现

• 证明了用于相干拉曼成像的毫秒级获取时间。
• 在约8 μm 的 PMMA 球体上实现约2.5倍的衍射极限空间分辨率提升 (~280 nm)。
• 在下转换的反斯塔克区域实现背景无探测，通过光子计数进行探测。
• 以约100 pJ 的脉冲能量探测宽带隙介电体、液体和微粒。
• 显示 XPM 引起的光谱展宽有助于在双梳设置中改进拉曼信号处理。