<title>Imaging of surface plasmons with a near-field microscope</title>

Abstract

Imaging of surface plasmon polaritons (SPP's) with a photon scanning tunneling microscope (PSTM) combined with shear force feedback is experimentally investigated. A contrast correction factor, that accounts for spatial frequency filtration performed by an uncoated fiber tip of the PSTM (when detecting the SPP intensity distribution), is introduced and evaluated from the measurements of a standing wave interference pattern formed by two counterpropagating evanescent waves, that are generated by total internal reflection of light beams inside a glass prism. Influence of propagating field components stemming from inelastic SPP scattering on the resultant intensity distributions and, consequently, on the near-field optical images obtained with the PSTM is discussed. Optical images taken at different tip-surface distances are used to evaluate the contribution from propagating field components in near-field optical images taken with shear force feedback. The approach developed is applied to experimental studies of elastic scattering of SPP's excited at the wavelength of 633 nm along smooth and rough surfaces of gold and silver films.

Elastic scattering of surface plasmon polaritons: Modeling and experiment

“…21 Such an approach allows one to circumvent the very complicated problem of SPP scattering by surface inhomogeneities and concentrate the efforts on various phenomena that were experimentally observed in ͑multiple͒ elastic SPP scattering. 4,8,[11][12][13]16 In this paper, we present numerical simulations of elastic SPP scattering by randomly located and specifically configured isotropic pointlike scatterers, and compare our calculations with the previously reported and additionally obtained experimental results. The paper is organized as follows.…”

“…The first assumption is justified by the experimental observations showing the appropriate interference patterns, whose periods corresponded to the interference between the incident and scattered SPP's, 4,[11][12][13]16 and signal ͑tip-surface͒ distance dependencies, that exhibited exponential behavior related to the evanescent decay of the SPP field. 8 In addition, recent theoretical results for an individual surface defect indicated that the elastic SPP scattering becomes dominant over the scattering out of the surface plane in the case of resonant SPP scattering. 18 The second assumption is primarily based on the circumstance that wellpronounced parabolic interference fringes were observed with SPP scattering by individual defects.…”

“…7 Lately our detailed experimental investigations demonstrated convincingly that, for the SPP being resonantly excited at a relatively smooth surface, near-field optical images ͑obtained with an uncoated fiber tip͒ can be indeed directly related to the intensity distributions of the total SPP field, i.e., field of the excited and ͑in-plane͒ scattered SPP's. 8 Hereafter, SPP scattering in the surface plane is denoted as elastic SPP scattering, since SPP scattering into a free space is an unwanted process leading to the additional ͑radiative͒ losses experienced by the SPP.…”

Direct observation of localized dipolar excitations on rough nanostructured surfaces

“…In general, one has to determine the transfer function of the fiber tip used ͑assuming that it can be considered as a passive probe 29 ͒, which is a challenging problem itself. 43 Taking into account that, for the spatial period of ϳ300 nm of the intensity interference pattern, the contrast correction factor is ϳ2, 43 one can deduce that the enhancement corresponding to the experimental images is at least 40 times. Alternatively, one can consider the imaging of bright spots with uncoated fiber tips that has been modeled theoretically.…”

Classical Plasmonics: Wave Propagation Control at Subwavelength Scale

“…1 were measured by using an illumination wavelength ¼ 632:8 nm and for two metallic smooth¯lms in order to determine the resonant excitation angle for the corresponding SPP. 52 The shape of the ATR curve was quantitatively described by using the three layer Fresnel equation. The calculated curve allows one to extract the dielectric constant of the¯lm from a¯t to the measured resonance spectrum.…”