[MOS] TODAY March 30, 2010

[Zina Queen]

Seminar on

Modern Optics and Spectroscopy

Two dimensional femtosecond stimulated Raman 
spectroscopy:  A new technique to probe 
vibrational anharmonicity

David McCamant,
University of Rochester

Tuesday, March 30, 2010

12:00 - 1:00 p.m.





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 Šhi, by the 
coherent motion of an impulsively driven mode, at 
frequency Šlow.  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.


Grier Room, MIT Bldg 34-401
Refreshments served after the lecture
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