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Hot carrier dynamics in a dispersionless plasmonic system

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.