Spectral Shift Of The Plasmon Resonance Between The Optical Extinction And Absorption Of Gold And Aluminum Nanodisks

Comparing the optical properties of plasmonic nanoparticles in terms of scattering, absorption and extinction is an active and delicate issue in nano-optics. Absorption cross sections are usually difficult to be reliably measured. In this work, the absorption of gold and aluminum nanodisks was measured using quantitative wavefront sensing. We evidence a spectral shift between the retrieved absorption and the extinction maxima. Discrete dipole approximation calculations enabled us to unravel the origins of the spectral shifts, which are different depending on the material. In the case of gold nanodisks, the mismatch between extinction and absorption (similar to 15 nm) is related to the frequency shift of the plasmonic field intensity between near-field and far field regimes, respectively probed through the heat generated within the nanoparticles and the optical extinction. For aluminum nanodisks, displaying dipolar plasmon resonances in the wavelength range 700 to 850 nm, the spectral shift between extinction and absorption is ascribed to the presence of interband transitions located on the low energy side of the surface plasmon