Propagation of femtosecond light pulses through near-field optical aperture probes

• Published in: Ultramicroscopy Vol. 92; no. 3; pp. 251 - 264
• Main Authors: Pack, A, Hietschold, M, Wannemacher, R
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2002; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Metals and metallic alloys; Near-field scanning optical microscopes; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optics; Physics; Scanning probe microscopes, components and techniques; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter; Transmission and absorption; Wave optics; Wave propagation; Wave propagation, transmission and absorption; 42.25.Bs; 78.47.+p; 78.66.Bz Subject index terms: 019; Wave propagation; Transmission and absorption; Metals and metallic alloys; 07.79.Fc; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter; Near-field scanning optical microscopes; Femtosecond; Ultrafast technique; Measuring methods; Near-field scanning optical microscopy; Experimental study; Optical pulse; Ultrafast optics
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/S0304-3991(02)00141-9

The propagation of femtosecond light pulses through near-field optical fiber tips has been modelled numerically in three spatial dimensions by means of the finite integration technique. Ideally conducting as well as real metallic coatings of the tip have been considered, and the influence of surface plasmon polaritons (SPP) on shape, spectrum, and amplitude of the light pulse in the near and far fields of the tip have been investigated in this way. Special attention has been devoted to the superluminal tunneling of light through the fiber tip. The variation of phase and group velocities along the fiber axis has been characterized for a number of real metals and for different tip angles. A maximum of both velocities in the near field of the tip is characteristic for coatings of finite conductivity. For some tip angles negative values of the phase and/or group velocities are observed, which are caused by the propagation of SPP on the outer surface of the coating and their conversion into photons. It is shown, that the excitation of SPP on the metallic coating leads to strongly altered spatial emission characteristics of the tip.