  Surface plasmon mediated hot carrier generation is widely utilized for the
manipulation of the electron-photon interactions in many types of
optoelectronic devices including solar cells, photodiodes, and optical
modulators. A diversity of plasmonic systems such as nanoparticles, resonators,
and waveguides have been introduced to enhance hot carrier generation; however,
the impact of the propagating surface plasmons on hot carrier lifetime has not
been clearly demonstrated. Here, we systematically study the hot carrier
relaxation in thin film gold (Au) samples under surface plasmon coupling with
the Kretschmann configuration. We observe that the locally confined electric
field at the surface of the metal significantly affects the hot carrier
distribution and electron temperature, which results in a slowing of the hot
electrons relaxation time, regardless of the average value of the absorbed
power in the Au thin film. This result could be extended to other plasmonic
nanostructures, enabling the control of hot carrier lifetimes throughout the
optical frequency range.
