受激拉曼相移光谱：获取超精细指纹光谱的新途径
Stimulated Raman phase shift spectroscopy: a pathway to hyperfine fingerprint spectra
AI总结：
本研究提出受激拉曼相移（SRPS）光谱技术，通过测量SRS引发的斯托克斯光场相移获取超窄δ函数型谱线，实验证实其谱峰更多、线宽窄4个数量级、信噪比提升14.3 dB，为材料超精细指纹表征提供新途径。
摘要：
本文论证了名为受激拉曼相移（stimulated Raman phase shift, SRPS）光谱的新型拉曼光谱技术的原理与实验实现。该技术通过测量受激拉曼散射（stimulated Raman scattering, SRS）引发的斯托克斯光场相移（Δϕ）实现检测，该相移与SRS的三阶非线性极化率的实部相关。理论上，1/|Δϕ|的谱线形状为δ函数波形，对斯托克斯光强波动、材料中声子的退相干以及非均匀荧光背景均不敏感。为测量1/|Δϕ|，研究人员研发了一套包含马赫-曾德尔干涉仪与信号处理装置的SRPS光谱仪。利用该光谱仪，研究人员同时检测了纯二甲基亚砜的SRPS光谱与受激拉曼增益（stimulated Raman gain, SRG）光谱。在SRPS光谱中观测到对应特定分子振动与转动模式的7个拉曼峰，而在无先验知识的情况下，SRG光谱中仅能识别出2个峰。在测得的SRPS光谱中，对应甲基的v_s(CH₃)伸缩模式、中心位于2913.283 cm⁻¹的拉曼峰线宽小于0.00036 cm⁻¹，比测得的SRG光谱中的该峰线宽窄近4个数量级。同时，该2913.283 cm⁻¹处拉曼峰的检测信噪比为25.3 dB，较SRG光谱提升了14.3 dB。10次独立测量验证了SRPS技术的可靠性，拉曼峰频率的标准偏差小于±0.338 cm⁻¹。SRPS技术为表征材料的超精细指纹特征开辟了新路径。
英文摘要：
The principle and experimental realization of a novel Raman spectroscopic technique entitled stimulated Raman phase shift (SRPS) spectroscopy was demonstrated. This technique depends on the measurement of the stimulated Raman scattering (SRS) induced phase shift of Stokes light field ($Δ$ $ϕ$) that is related to the real part of the third order nonlinear susceptibility of SRS. In principle, the spectral lineshape of 1/|$Δ$ $ϕ$| is a delta function waveform, which is insensitive to the fluctuation of Stokes light intensity, the decoherence of phonon in materials, as well as the inhomogeneous fluorescence background. In order to measure 1/|$Δ$ $ϕ$|, a SRPS including a Mach-Zender interferometer and a signal processing device was developed. Using the developed spectrometer, the SRPS and stimulated Raman gain (SRG) spectra of neat dimethyl sulfoxide were detected simultaneously. Seven Raman peaks corresponding to specific molecule vibrational and rotational modes were observed in the SRPS spectra, while only two peaks could be identified in the SRG spectra without a priori knowledge. The linewidth of the Raman peak centered at 2913.283 cm$^{-1}$ indicating the v$_s$(CH$_3$)stretching mode of the methyl groups was less than 0.00036 cm$^{-1}$ in the measured SRPS spectra, which was almost four orders of magnitude narrower than that in the measured SRG spectra. Meanwhile, the detection signal-to-noise ratio of the Raman peak centered at 2913.283 cm$^{-1}$ was 25.3 dB, representing an increase of 14.3 dB compared to the SRG spectra. The reliability of SRPS technique was verified by 10 independent measurements, and the standard deviation of the Raman peak frequency was less than $\pm$0.338 cm$^{-1}$ . The SRPS technique paves the way for characterizing the hyperfine fingerprint of materials.
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