Surface‐Plasmon‐Assisted Control of Ultrafast Optical Relaxation Traces

Abstract The time‐dependent response of a material to a short laser pulse excitation directly reflects ultrafast physical processes within the material. In optical pump‐probe experiments these processes can be observed due to laser‐induced modification of material dielectric permittivity. In nanostructured systems resonant sensitivity of optical response to dielectric permittivity may provide a strong dependence of the relaxation trace on the probe wavelength. In this work, an anomalous wavelength‐dependent temperature nonlinearity of the optical response of a plasmonic crystal on the picosecond timescale is shown, controlled by the system parameters and observed in the spectral vicinity of a surface plasmon resonance. A practical method for adjusting the picosecond relaxation traces of optical response is proposed on the basis of resonant probe. The effect is demonstrated experimentally and numerically. The phenomenological description is proposed.