Optical near-field absorption at a metal tip far from plasmonic resonance

We investigate the wavelength and the polarization dependence of the absorption of a subwavelength tip illuminated by an ultrashort laser pulse using laser-assisted atom-probe tomography. We show that it is possible to localize the absorption at the tip apex by choosing the appropriate laser polarization and wavelength even for excitation wavelength far from the plasmonic resonance. This effect can be explained by the diffraction theory of Sommerfeld applied on a tip geometry. Furthermore, numerical calculations are performed on a real subwavelength tip to confirm this absorption localization and to explain the role of the polarization and the wavelength.