  Hot carrier dynamics in a dispersionless plasmonic structures over a broad
wavelength are studied by pump-probe measurements with 45 fs time resolution.
The role of direct excited as well as plasmon generated hot carriers on low
energy probe plasmons are studied by simultaneous measurement of differential
transmittance and reflectance. While the pump fluence dependence on the decay
times is linear for hot electrons and plasmon generated hot electrons, when
pump is near resonant with the X- symmetry point, decay time varied as square
of pump fluence. Decay times of 800 nm degenerate pump-probe measurements
highlight the difference in surface (reflection) and the bulk (transmission)
mechanisms. Decay time corresponding to the hot carrier relaxation is in the 1
-3 ps range for different excitation energies. Rise time, governed by the
plasmon to hot carrier conversion and electron - electron scattering processes,
is about 200 fs for the hot carrier and hot plasmon excitation cases which
increased to about 485 fs for when pump is resonant with interband transition
at X- symmetry point.
