Nonlinear Optical Studies of Interfaces

Second-order nonlinear optical processes such as Second Harmonic Generation and Sum-Frequency Generation are excellent optical techniques for probing the interface phenomena due to their interface specificity and submonolayer sensitivity with non-invasive and in-situ advantages.

Sum-Frequency Generation (
SFG is a second-order nonlinear process in which visible (ωvis) and IR (ωIR) photons combine at the surface or interface and generate a third photon (ωSFG) whose frequency is the sum of the two frequencies: ωSFG = ωIR + ωvis.


Surface Vibrational Spectroscopy:

By tuning the IR frequency to match the vibrational mode of the molecule of interest, SFG provides the surface vibrational spectra of surface or interface species.



Surface vibrational dynamics (population dynamics):

IR pump-SFG probe is used to probe the rate of energy transfer and population relaxation of interfacial species. We have shown that the vibrational dynamics of interfacial water at a silica surface is different from bulk water and depends on the charged surface.


Surface vibrational dynamics (vibrational dephasing dynamics):

SFG-FID is used to probe the dephasing of the vibrational modes of interfacial species.


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