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| Femtosecond Stimulated Raman Line Shapes: Dependence on Resonance Conditions of Pump and Probe Pulses |
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Cheng Chen1, Liang-dong Zhu1,2, Chong Fang1,2
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1.Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon, 97331-4003, USA;2.Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, Oregon, 97331-6507, USA
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| Abstract: |
| Resonance enhancement has been increasingly employed in the emergent femtosecond stimulated Raman spectroscopy (FSRS) to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint efforts by the technique-and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. During spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Raman pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodamine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by different resonance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence (HL) pathways. Meanwhile, on-resonance conditions of the Raman pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences. |
| Key words: Femtosecond stimulated Raman spectroscopy Resonance enhancement Raman pump and probe pulses Wavelength tunability Dispersive line shapes Stokes and anti-Stokes FSRS |
| FundProject:The work was supported by the U.S. National Science Foundation CAREER grant (CHE-1455353) and the Oregon State University (OSU) Research Equipment Reserve Fund (Spring 2014) to C. Fang (USTC 9603). We also thank the Wei Family Private Foundation in supporting C. Chen (USTC 0903) during his graduate studies at OSU Chemistry. |
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| 飞秒受激拉曼光谱线形:基于泵浦及探测脉冲光的共振条件研究 |
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陈成1, 朱良栋1,2, 方翀1,2
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1.美国俄勒冈州立大学化学系, 俄勒冈州, 科瓦利斯 97331-4003;2.美国俄勒冈州立大学物理系, 俄勒冈州, 科瓦利斯 97331-6507
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| DOI：10.1063/1674-0068/31/cjcp1805125 |
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