Excitation and propagation of surface plasmon polaritons on the gold covered conical tip

Shape effects in tapered metal rods during adiabatic nanofocusing of plasmons

“…This phenomenon is called nanofocusing and it cannot be achieved in conventional optics using dielectric focusing elements that are subject to the diffraction limit of light ͑which does not allow concentration of light energy into regions that are much smaller than the wavelength of light in the medium͒. 15,18,19 Nanofocusing in metallic nanostructures such as tapered rods and tapered optical fibers with metal coating have been studied and analyzed [20][21][22][23][24][25][26][27][28] along with other numerous structures such as tapered circular paraboloidal, 29 metallic gaps and nanowedges, [30][31][32][33][34][35] tapered metal films, 36 nanoparticle lenses, 37,38 and pyramid tips covered in a metal film. 39 A tapered optical fiber coated in thin metal film with a small nanosized hole at the tip ͑optical probe͒ is a wellknown and important component in the near-field scanning optical microscopy, capable of achieving nanoscale resolution.…”

“…In addition, the presence of the metal film covering the tapered fiber usually introduces significant perturbations in the optical signals obtained from the described probes. 15,16 A possible solution of these difficulties is offered by plasmon nanofocusing in a tapered metal rod [22][23][24][25][26][27][28] which could be used instead of the tapered optical fiber with a metal film. Tapered rods are capable of focusing light energy into regions as small as a few nanometers with a substantial local electromagnetic field enhancement ͑up to hundreds of times͒ near the tip.…”

Local electric field enhancement during nanofocusing of plasmons by a tapered gap

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] It offers unique opportunities for the development of near-field optical microscopy with subwavelength resolution, [7][8][9][10][11][12][13][14][15] high-resolution lithography, 16 coupling of light into and out of photonic nanocircuits, 5,17 new sensors and detection techniques based on surface-enhanced Raman scattering, 8,[18][19][20] etc. Different metal structures have been suggested for nanofocusing of plasmons.…”

“…One of the major features of these structures is the possibility of strong local field enhancement in regions that are much smaller than the wavelength. [3][4][5][6][7][8][9][10][11][12]20 This opens unique opportunities for observation of nonlinear plasmonic effects and development of new sensors, for example, based on surfaceenhanced Raman scattering in metal structures with nanofocusing. 8,[18][19][20] At the same time, it is still not clear which of these structures will be most efficient in terms of achieving the largest possible local field enhancement.…”

Novel SNOM Probes Based on Nanofocusing in Asymmetric Structures

“…At a certain value of 1 r , the wavevector of the WGM can match the one of the SPP mode: in these conditions, energy transfer from the WGM into the SPP mode is possible and, as a result, surface plasmons are excited bringing about nanofocusing. The transfer of energy and the field profiles can be determined with this approach using the coupled mode theory [41,42]. In this way, the SPPs can be excited using the WGM, thereby overcoming the problem of background inherent in the use of fully metal probes under external illumination.…”