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Download fileRelative Phase Change of Nearby Resonances in Temporally Delayed Sum Frequency Spectra
journal contribution
posted on 2015-12-16, 22:08 authored by Fadel
Y. Shalhout, Sergey Malyk, Alexander V. BenderskiiSurface-selective sum frequency generation (SFG) spectroscopy
has
been previously shown to benefit from a finite time delay between
two input laser pulses, which suppresses the nonresonant background
and improves spectral resolution. Here we demonstrate another consequence
of the time delay in SFG: depending on the magnitude of the delay,
nearby resonances (e.g., vibrational modes) can “flip”
their relative phase, i.e., appear either in-phase or out-of-phase
with one another, resulting in either constructive or destructive
interference in SFG spectra. This is significant for interpretation
of the SFG spectra, in particular because the sign of the resonant
amplitude provides the absolute molecular orientation (up vs down)
of the vibrational chromophore. We present results and model calculations
for symmetric and asymmetric CH-stretch modes of the methyl-terminated
Si(111) surface, showing that the phase flip occurs when the delay
matches half-cycle of the difference frequency between the two modes.