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Junction Plasmon Driven Population Inversion of Molecular Vibrations: A Picosecond Surface-Enhanced Raman Spectroscopy Study
journal contribution
posted on 2018-07-31, 00:00 authored by Kevin T. Crampton, Alexander Fast, Eric O. Potma, V. Ara ApkarianMolecular
surface-enhanced Raman spectra recorded at single plasmonic
nanojunctions using a 7 ps pulse train exhibit vibrational up-pumping
and population inversion. The process is assigned to plasmon-driven,
dark, impulsive electron-vibration (e-v) excitation. Both optical
(Raman) pumping and hot-electron mediated excitation can be rejected
by the characteristic spectra, which allow the simultaneous measurement
of vibrational temperature of the molecules and electronic temperature
of the metal. Vibrational populations are determined from anti-Stokes
to Stokes intensity ratios, while the electron temperature is obtained
from the anti-Stokes branch of the electronic Raman scattering continuum.
Population inversion survives in high-frequency vibrations that effectively
decouple from the metal.