Scanning near-field optical microscopy (SNOM) is an imaging technique that can work beyond the diffraction limit. It can do this by collecting the non-propagating evanescent field, which exists up to a few nanometres away from a sample's surface. This is achieved by positioning a very small aperture (usually a glass fibre heated and pulled down to form a sharp tip) just a few nanometres from a sample's surface.
Surpassing the resolution of standard optical microscopes, SNOM can investigate the local electric field properties of devices that have features much smaller than the wavelength of light under study. The resolution of SNOM is limited by the aperture size of the collector, rather than the wavelength of light used to image.
Our group uses SNOM's unique ability of collecting the evanescent wave to investigate the properties of waveguides. We have studied the electric field behaviour inside fibre Bragg gratings, the mode profiles in micro-structured fibres, supercontinuum generation in highly nonlinear waveguides, and the inter-modal delay of pulses inside waveguides. Within the group, we have the unusual ability to combine ultra-fast science with the high-spatial resolution of SNOM. This ability enables us to investigate phenomena with femtosecond time resolutions and nanometre spatial resolutions.