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<div align="center"><font face="Times New Roman"
color="#000000"><b>Seminar on</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Modern Optics and Spectroscopy</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><i><b>Two dimensional femtosecond stimulated Raman
spectroscopy: A new technique to probe vibrational
anharmonicity</b></i></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>David McCamant</b>,</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">University of Rochester</font></div>
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<div align="center"><font face="Times New Roman"
color="#000000">Tuesday, March 30, 2010</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">12:00
- 1:00 p.m.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">A new
methodology for two-dimensional Raman spectroscopy -termed
two-dimensional femtosecond stimulated Raman spectroscopy (2D-FSRS)-
will be discussed, including recent experimental results for
acetonitrile and chloroform. This technique uses three different
ultrafast laser pulses to perform an experiment similar to previous
5th-order Raman experiments. 2D-FSRS can potentially observe
molecular anharmonicity by measuring the modulation of the frequency
of a probed Raman mode, at frequency</font><font face="Symbol"
color="#000000"> Š</font><font face="Times New Roman"
color="#000000">hi, by the coherent motion of an impulsively driven
mode, at frequency</font><font face="Symbol" color="#000000">
Š</font><font face="Times New Roman" color="#000000">low. For
instance, in acetonitrile, the signal is generated by driving the CCN
bend (379 cm-1) and CC stretch (920 cm-1) into coherence via impulsive
stimulated Raman scattering and subsequently probing the stimulated
Raman spectrum of the CC stretch, the CN stretch (2250 cm-1) and the
CH stretch (2942 cm-1). The resultant signal can be generated by
two alternative mechanisms: a fifth-order Raman process that would
directly probe anharmonic coupling between the two modes, or a
third-order cascade in which a third-order coherent Raman process
produces a field that goes on to participate in a third-order
stimulated Raman transition. Our theoretical and experimental
results show that the third-order cascade dominates the spectra in the
current implementation of 2D-FSRS. Our classical model shows
that the cascade signal can be accurately predicted using the known
parameters of the 1D Raman spectrum. However, understanding the
mechanism of cascade generation is important for those interested in
developing higher-order Raman techniques.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">Grier
Room, MIT Bldg 34-401</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Refreshments served after the lecture</font></div>
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