CC BY
0Ultrafast hot electron diffusion in nickel one-dimensional
plasmonic crystals
M.A. Kiryanov*, I.A. Novikov, A.Y. Frolov. T.V. Dolgova. A.A. Fedyanin
Faculty of Physics, Lomonosov Moscow State University, Moscow, 119991 Russia
* kiryanovma@my.msu.ru
One of the promising fields of nanophotonics is studying plasmonic crystal optical response on external stimulus such as a femtosecond laser radiation. An ultrashort "pump" pulse heats electron gas of metals and modifies dielectric permittivity. The induced changes can be observed by measuring reflectance or transmittance of a "probe" pulse. Plasmonic crystals reflectance or transmittance spectra are sensitive to dielectric permittivity changes near a resonance, therefore they can be used to significantly enhance thermooptical response. Evolution of a plasmonic crystal optical response is described by hot electron dynamics inside a metal. In case of a nanostructured surface electric field localization of "pump" and "probe" pulses inside plasmonic crystal may be spatially inhomogeneous, which allows detection of hot electron diffusion along surface.
In this work, ultrafast differential reflectance of reference nickel plate and three nickel one-dimensional plasmonic crystals with the sinusoidal surface shape, the same spatial period, and different corrugation depths were measured by femtosecond spectroscopy "pump-probe" technique. Differential reflectance time traces at resonant wavelength of plasmonic crystals showed considerably slower dynamics compared to reference plate and literature: both rise and relaxation of differential reflectance took longer time. The lag became more pronounced with corrugation depth increase. The effect is associated with inhomogeneous absorbing of pump pulse by nickel concentrated at the bottoms of the plasmonic crystal, consequent transfer of hot electrons along sides of the plasmonic crystal up to the tops and detection of entire surface temperature by resonant probe pulse. To confirm this interpretation combined two-temperature and electromagnetic calculation were done.
