近日，北京大学的熊汗青及其研究团队取得一项新进展。经过不懈努力，他们成功实现瞬态受激拉曼散射光谱与成像技术突破。相关研究成果已于2024年3月8日在国际知名学术期刊《光：科学与应用》上发表。

该研究团队报道了瞬态受激拉曼散射(T-SRS)，这是一种替代的时域策略，其绕过了所有基本共轭。T-SRS的实现依赖于量子相干操纵技术：研究人员通过精心设计的飞秒脉冲序列，成功激发了振动波包的干涉，并将这些干涉效应编码到受激拉曼损耗（SRL）信号中的振动振荡上。随后，通过对时域SRL信号进行傅里叶变换，便可获得拉曼光谱。由于T-SRS能够同时激发所有拉曼模式，因此具有自然线宽限制的谱线形状，光谱范围由激光带宽决定，并且灵敏度得到了显著提升。

使用约150飞秒的激光脉冲，研究人员成功将典型拉曼模式的灵敏度提高到了亚毫米级。借助全平面镜高速延时扫描技术，研究人员进一步展示了T-SRS在活细胞代谢的高光谱SRS成像以及高密度多路复用成像方面的卓越能力，其光谱分辨率达到了自然线宽极限。可以预见，T-SRS将在先进拉曼成像领域找到有价值的应用。

据悉，受激拉曼散射(SRS)近年来发展成为化学成像中必不可少的定量对比方法。然而，虽然最先进的自发拉曼显微镜可以常规地获得接近自然线宽极限的光谱线，但对于当前主流的SRS成像方法来说，光谱展宽是不可避免的。这是因为这些SRS信号都是在频域中测量的。在灵敏度和光谱分辨率之间存在妥协: 由于非线性过程受益于脉冲激励，基本的时间-能量不确定性限制了光谱分辨率。此外，光谱范围和捕获速度是相互制约的。

附：英文原文

Title: Transient stimulated Raman scattering spectroscopy and imaging

Author: Yu, Qiaozhi, Yao, Zhengjian, Zhou, Jiaqi, Yu, Wenhao, Zhuang, Chenjie, Qi, Yafeng, Xiong, Hanqing

Issue&Volume: 2024-03-08

Abstract: Stimulated Raman scattering (SRS) has been developed as an essential quantitative contrast for chemical imaging in recent years. However, while spectral lines near the natural linewidth limit can be routinely achieved by state-of-the-art spontaneous Raman microscopes, spectral broadening is inevitable for current mainstream SRS imaging methods. This is because those SRS signals are all measured in the frequency domain. There is a compromise between sensitivity and spectral resolution: as the nonlinear process benefits from pulsed excitations, the fundamental time-energy uncertainty limits the spectral resolution. Besides, the spectral range and acquisition speed are mutually restricted. Here we report transient stimulated Raman scattering (T-SRS), an alternative time-domain strategy that bypasses all these fundamental conjugations. T-SRS is achieved by quantum coherence manipulation: we encode the vibrational oscillations in the stimulated Raman loss (SRL) signal by femtosecond pulse-pair sequence excited vibrational wave packet interference. The Raman spectrum was then achieved by Fourier transform of the time-domain SRL signal. Since all Raman modes are impulsively and simultaneously excited, T-SRS features the natural-linewidth-limit spectral line shapes, laser-bandwidth-determined spectral range, and improved sensitivity. With ~150-fs laser pulses, we boost the sensitivity of typical Raman modes to the sub-mM level. With all-plane-mirror high-speed time-delay scanning, we further demonstrated hyperspectral SRS imaging of live-cell metabolism and high-density multiplexed imaging with the natural-linewidth-limit spectral resolution. T-SRS shall find valuable applications for advanced Raman imaging.

DOI: 10.1038/s41377-024-01412-6

Source: https://www.nature.com/articles/s41377-024-01412-6