Imaging beyond diffraction limit - prospectives for the NIR

Spectral imaging is diffraction limited and therefore features smaller than half a wavelength cannot be resolved. Nevertheless the life sciences and materials research demand for laterally high-resolved insights with chemical information below the resolution limit of light. A special approach e.g. to circumvent the diffraction limit is superresolution microscopy. The Stimulated Emission Depletion Microscope (STED) creates nearly spherical focal spots of 40–45 nm (λ /16) in diameter. Major drawbacks are the restriction to fluorescence and the need for high excitation intensities in the order of 1000 to 30000 solar units which limits cell viability. A further approach takes advantage of Scanning Probe Microscopy (SPM). The combination of SPM and near-field optical microscopy allows the characterization of the morphology and the chemistry of surfaces and cell structures beyond the diffraction limit and is called Scanning Near-Field Optical Microscopy (SNOM). An example of a dielectric near-field probe for SNOM is a so-called Solid Immersion Lens (SIL). The SIL is attached to a Micro-Spectral-Photometer for near-field spectroscopy. The SIL-system enhances the resolution up to λ /20 and improves the S/N ratio due to the high transmission efficiency. The SIL near-field setup has already proven its performance in the UV/VIS-range with a lateral resolution of 30 nm. A strategy and experiments are presented to extend the use of a SIL for NIR applications