Near-field scanning optical microscopy (NSOM)
About this technique
Near-field scanning optical Microscopy (NSOM) is an imaging technique that visually studies the optical properties (e.g. reflectivity, light emission/transmission/scattering, fluorescence) of a sample with a spatial resolution of tens of nanometres. Optical microscopy is limited by the diffraction limit, whereas the resolution for NSOM is dependent on the size of the optical probe, thus high spatial resolution of approximately 20 to 100 nm can be obtained for a variety of optical properties.
Conventionally, NSOM uses a sub-wavelength sized aperture in a metal coating of the optical fibre tip or cantilever, which is used to transfer the optical signal to and from the sample. Similar to atomic force microscopy, the probe rasters across the surface of the sample and the probe is used to channel the optical signal to and from the sample. Advances in scanning probe microscopy and its integration with optics and new near-field techniques has enabled modes such as apertureless NSOM, scattering NSOM, tip enhanced Raman/fluorescence and STM light emission.
Analysis of various samples (opaque or transparent) can be done with minimal sample preparation and a custom probe can be used for a particular sample. Applications for this technique extend to materials science, life science, nanophotonics (plasmonics, photonic crystals and waveguides), laser technology, optical micro-devices and nanotechnology.