Applications of field-enhanced near-field optical microscopy

Abstract

Metal nanostructures such as sharp tips can enhance emission yields through shape-induced local field enhancement. The enhancement originates from two mechanisms: surface plasmons and electrostatic lightening rod effects. We present fluorescence imaging using the strong local field created at the apex of a gold tip and demonstrate optical resolution of 25 nm: The enhancement effect gives also rise to photoemission from the tip itself. Measured spectra of the tip emission show a broad band continuum together with a second-harmonic peak. Both continuum and secondharmonic are confined at the apex of the tip. We find that, depending on the spectral position, the photoluminescence originates either from intraband or from interband transitions. The nonlinear response can be described by a single dipole oscillating at the second-harmonic frequency and oriented along the tip axis. These unique properties can be used to map focal fields distributions. r

Spectroscopic properties of a two-level atom interacting with a complex spherical nanoshell

“…The theory presented earlier in Ref. [12] with numerical results shown here may also stimulate design of coated tip geometries for applications in near-field optical microscopy [35].…”

“…(An expression for the dipole source intensity detected by a point detector has been provided by Dung et al [8] (see Eqs. (34)(35)(36) …”

“…Note also that metals per se have inherent photoluminescence [57]. However, since metal photoluminescence results in a broad band continuum [35,57], it can easily be filtered out.…”

Coupling of surface waves in highly defined one-dimensional porous silicon photonic crystals for gas sensing applications

“…In the past years, surface plasmon resonance 1 ͑SPR͒ phenomena reached wide popularity in a number of different domains such as nonlinear optics, 2 near-field microscopy/ spectroscopy, 3,4 and gas sensing. 5 This large interest is mainly connected to two important features of surface plasmon polaritons ͑SPPs͒: their strong electromagnetic field enhancement and their sensitivity upon changes of the refractive index at metal/dielectric interfaces.…”

Fabrication of nanostructures with high electrical conductivity on silicon surfaces using a laser-assisted scanning tunneling microscope

“…The simulation results show that an electric field in parallel with the tip axis is required to achieve a strongly enhanced optical field underneath the tip apex, which is in agreement with the previous reports. 29,30 Lightning rod effects can be used to explain this enhancement phenomenon. The free electrons in the tip react to the external electromagnetic excitation by inducing surface charges.…”