Near-field Optical Excitation Research Articles

Fabrication of a Near-Field Optical Fiber Probe with a Nanometric Metallized Protrusion

We have developed a novel probe with a nanometric metallized protrusion extending through a subwavelength aperture to increase optical near-field excitation and collection efficiencies. The apex diameter of the fabricated metallized protrusion was 35 nm. The Intensity distribution of the optical near-field at the apex of the probe was measured by scanning another probe across the apex, and it was observed that strong optical near-field was generated at the apex of the metallized protrusion. The width of the intensity distribution was 150 nm including instrumental resolution. Probes with spherical and ellipsoidal metallized protrusion were also fabricated, by which enhancement of the optical near-field is expected due to localized plasmon excitation.

Near-Field Surface-Enhanced Raman Spectroscopy on Single Silver Nanoparticles

We report the development of a near-field Raman microscope for nanometer-scale vibrational spectroscopy at room temperature. With the use of surface-enhanced Raman scattering and tapered single-mode fiber probes, near-field Raman spectra have been obtained from single Ag colloidal nanoparticles with excitation intensities as low as 10 nW. Far-field confocal studies have also been carried out on spatially isolated, single Ag nanoparticles. A direct comparison of the near-field and confocal results shows that near-field optical excitation does not lead to significantly different selection rules in Raman spectroscopy. This work further demonstrates that single metallic nanoparticles can be attached to the tip of a near-field probe for potential application in surface-enhanced optical microscopy and nanofabrication.

Single molecule detection and photochemistry on a surface using near-field optical excitation.

We report the first photobleaching experiments of single molecules on a surface. Single molecules of rhodamine 6G are detected on a silica surface under ambient conditions using near-field scanning optical microscopy. Photobleaching of an individual molecule appears as an abrupt disappearance of fluorescence after seconds of constant excitation. Other reversible, upward and downward changes in fluorescence are observed, possibly due to reorientation of molecules on the surface.