We present a new scheme for near-field fluorescence imaging using a metal tip illuminated with femtosecond laser pulses of proper polarization. The strongly enhanced electric field at the metal tip (ø15 nm end diameter) results in a localized excitation source for molecular fluorescence. Excitation of the sample via two-photon absorption provides good image contrast due to the quadratic intensi...

A scanning near-field optical microscope (SNOM) is a powerful tool to investigate optical effects that are smaller than Abbe’s limit. Its greatest strength is the simultaneous measurement of high-resolution topography and optical near-field data that can be correlated to each other. However, the resolution of an aperture SNOM is always limited by the probe. It is a technical challenge to fabric...

The method of fluorescence resonance energy transfer scanning near-field optical microscopy (FRET SNOM) consists in the separation of a FRET pair between an SNOM tip and a sample. The donor (or acceptor) centre is located at the tip apex and scanned in the vicinity of a sample while acceptor fluorescence (or donor-fluorescence quenching) is detected. It is shown that the spatial resolution for ...

We discuss experimental studies of the interaction between a nanoscopic object and a photonic crystal membrane resonator of quality factor Q=55000. By controlled actuation of a glass fiber tip in the near field of the photonic crystal, we constructed a complete spatio-spectral map of the resonator mode and its coupling with the fiber tip. On the one hand, our findings demonstrate that scanning ...

We present a new method of measuring optical near-fields within ~1 nm of a metal surface based on rescattering of photoemitted electrons. With this method, we precisely measure the field enhancement factor for tungsten and gold nanotips as a function of tip radius. The agreement with Maxwell simulations is very good. Further simulations yield a field enhancement map for all materials, which sho...

The stress field near the tip of a crack in a plate subjected to membrane and bending loads and undergoing large deflections, is investigated by performing an asymptotic analysis in the context of von Karman plate theory. It is demonstrated that the character of the near tip fields is identical to those of the linear plate theory. However, the determination of the crack tip stress intensity fac...

Polarization properties of apertureless-type scanning near-field optical microscopy (a-SNOM) were measured experimentally and were also analyzed using a finite-difference time-domain (FDTD) simulation. Our study reveals that the polarization properties in the a-SNOM are maintained and the a-SNOM works as a wave plate expressed by a Jones matrix. The measured signals obtained by the lock-in dete...

Environmental noise restrictions play a role in the performance of wind turbines and the dominant source of noise on modern turbines is aeroacoustic noise produced by the blades. A 32 sensor acoustic array has been developed in cooperation between the National Renewable Energy Laboratory (NREL) and the University of Colorado to conduct measurements of aeroacoustic noise from a 100 kW wind turbi...

An apertureless near-field scanning optical microscope (ANSOM) that utilizes the enhanced field around a gold nanosphere, which is attached to the end of an atomic force microscope (AFM) tip, is used to image the local dielectric constant of the patterned metallic surfaces and local electric field around plasmonic nanosphere samples. A colloidal gold nanosphere (approximately 50 nm diameter) is...

Nanoscale ridge apertures provide a highly confined radiation spot with a high transmission efficiency when used in the near field approach. The radiation confinement and enhancement is due to the electric–magnetic field concentrated in the gap between the ridges. This paper reports the experimental demonstration of radiation enhancement using such antenna apertures and lithography of nanometer...