Near-Field Scanning Optical Microscopy
For ultra-high optical resolution, near-field scanning optical microscopy (NSOM) is currently the photonic instrument of choice. Near-field imaging occurs when a sub-micron optical probe is positioned a very short distance from the sample and light is transmitted through a small aperture at the tip of this probe. The near-field is defined as the region above a surface with dimensions less than a single wavelength of the light incident on the surface. Within the near-field region evanescent light is not diffraction limited and nanometer spatial resolution is possible. This phenomenon enables non-diffraction limited imaging and spectroscopy of a sample that is simply not possible with conventional optical imaging techniques.
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Near-Field Scanning Optical Microscopy
Introduction
A principle in diffraction-limited optical microscopy requires that the spatial resolution of an image is limited by the wavelength of the incident light and by the numerical apertures of the condenser and objective lens systems.
Near-Field Scanning Optical Microscopy (NSOM) Probes
The optical probe is the most critical part of the near-field microscope for achieving high resolution images. This section introduces a few of the methods that are commonly used in near-field microscopy.