KEYWORDS: Thin films, Gold, Surface plasmons, Near field, Metals, Waveguides, Near field scanning optical microscopy, Optical fibers, Near field optics, Light wave propagation
Randomly distributed small holes of various subwavelength sizes were fabricated in a thin gold film. We have studied the optical near-filed transmission of the film. In the wavelength spectrum from 350nm to 650nm, a number of strongly enhanced transmission peaks were observed. These transmission peaks can only been observed in the near field. We attribute the new phenomenon to the surface plasmon coupling inside the holes and between the surfaces on the two sides of the thin film. We have also observed that the thin film support two-dimensional wave guiding and the guided light has a red shift of 200nm. Finally, we have observed strong second-harmonic radiation from the thin films with a pulsed laser of wavelength 1064nm. Strong second-harmonic radiation was observed at the wavelength of 532nm with a halfwidth of 40nm.
KEYWORDS: Near field scanning optical microscopy, Optical spheres, Near field, Near field optics, Optical microscopy, Polarization, Silver, Optical engineering, Reflection, Radio propagation
KEYWORDS: Near field scanning optical microscopy, Optical spheres, Near field, Near field optics, Optical microscopy, Silver, Radio propagation, Wave propagation, Polarizability, Polarization
We present a numerical comparison between shear-force, constant-height and constant-intensity images in scanning near-field optical microscopy. We demonstrate the general difference between the three images. Two type of incident light are tested of polarization in perpendicular and parallel direction with respect to the mean plane of the surface. Merits and demerits of the three images are discussed.
We demonstrate theoretically that for polychromatic incident light of Gaussian spectrum, a dipole radiates with a redshifted spectrum. The degree of the shift depends on the radiation distance. The shift disappears in far field limit. These spectral changes are not caused by dispersive optical response of the source, nor stemming from correlations in distributions of source or scattering medium. Therefore, the demonstrated spectral changes are due to the nearness of the observation point. In other words, one states that the near field spectra, in general, bear a redshift with respect to the far field spectra.
KEYWORDS: Near field scanning optical microscopy, Reflection, Wave propagation, Optical spheres, Near field, Light wave propagation, Near field optics, Optical microscopes, Silver, Optical microscopy
A theory to decompose the propagating waves and the evanescent field in the optical dipole radiation is applied to analyze the reflection near-field optical microscopy. It is theoretically and numerically demonstrated that a local field vertically polarized toward the sample surface at the very end of the probe will provide a longer evanescent field tail into the gap between the probe and the sample and, hence, will improve the imaging quality of the microscope.
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