Technology Human Resource Support for SMEs Center, Korea Institute of Industrial Technology (KITECH), Cheonan 31056, Republic of Korea.
R&D Center, Uniotech, Daejeon 34013, Republic of Korea.
J Phys Chem B. 2023 May 4;127(17):3958-3968. doi: 10.1021/acs.jpcb.3c00926. Epub 2023 Apr 19.
The spectral congestion of highly overlapping vibrational peaks of molecules in condensed phases is a persistent challenge in conventional linear vibrational spectroscopy, making it difficult to accurately determine the spectroscopic parameters. This study demonstrates the utility of time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy with a time-delayed picosecond probe pulse in resolving congested C-H stretching vibrational peaks of condensed organic matters. The results show that the overlapping vibrational peaks of polymeric films and oily liquids, which are not easily distinguishable in spontaneous Raman spectroscopy, can be separated in the time-resolved CARS (tr-CARS) spectra. To understand the physical basis of the enhanced spectral resolution, we examine the time series of CARS spectra obtained by varying the delay time between the pump and probe pulses. The global fit analysis indicates that the effective suppression of faster Raman free-induction-decay components and instantaneous nonresonant background signals contributes to improved spectral resolution. Additionally, the present study reveals that the CARS spectra at a sufficient probe delay time are highly sensitive to the incident and detection polarizations, further improving vibrational peak distinguishability through polarization-controlled tr-CARS.
在凝聚相的分子中，高度重叠的振动峰的光谱拥挤是传统线性振动光谱学中的一个持续挑战，使得难以准确确定光谱参数。本研究展示了时间和频率分辨相干反斯托克斯拉曼散射（CARS）光谱学的实用性，该光谱学具有延迟皮秒探测脉冲，可用于解析凝聚态有机物质中拥挤的 C-H 伸缩振动峰。结果表明，在自发拉曼光谱中不易区分的聚合膜和油性液体的重叠振动峰，可以在时间分辨 CARS（tr-CARS）光谱中分离。为了理解增强光谱分辨率的物理基础，我们通过改变泵浦和探测脉冲之间的延迟时间来检查获得的 CARS 光谱的时间序列。全局拟合分析表明，对更快的拉曼自由感应衰减分量和瞬时非共振背景信号的有效抑制有助于提高光谱分辨率。此外，本研究表明，在足够的探测延迟时间下，CARS 光谱对入射和探测偏振高度敏感，通过偏振控制 tr-CARS 进一步提高了振动峰的可分辨性。
