Influence of Electronic Resonances on Mode Selective Excitation with Tailored Laser Pulses

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• 作者：J. Konradi ; A. Gaá ; l ; A. Scaria ; V. Namboodiri ; A. Materny
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：February 21, 2008
• 年：2008
• 卷：112
• 期：7
• 页码：1380 - 1391
• 全文大小：566K
• 年卷期：v.112,no.7(February 21, 2008)
• ISSN：1520-5215

文摘

Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) gives access to ultrafast moleculardynamics. However, the gain of the temporal resolution entails a poor spectral resolution due to the inherentspectral width of the femtosecond excitation pulses. Modifications of the phase shape of one of the excitingpulses results in dramatic changes of the mode distribution reflected in coherent anti-Stokes Raman spectra.A feedback-controlled optimization of specific modes making use of phase and/or amplitude modulation ofthe pump laser pulse is applied to selectively influence the anti-Stokes signal spectrum. The optimizationexperiments are performed under electronically nonresonant and resonant conditions. The results are comparedand the role of electronic resonances is analyzed. It can be clearly demonstrated that these resonances are ofimportance for a selective excitation by means of phase and amplitude modulation. The mode selectiveexcitation under nonresonant conditions is determined mainly by the variation of the spectral phase of thelaser pulse. Here, the modulation of the spectral amplitudes only has little influence on the mode ratios. Incontrast to this, the phase as well as amplitude modulation contributes considerably to the control processunder resonant conditions. A careful analysis of the experimental results reveals information about themechanisms of the mode control, which partially involve molecular dynamics in the electronic states.