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Low‐temperature scanning system for near‐ and far‐field optical investigations

A combined system for far‐ and near‐field optical spectroscopy consisting of a compact scanning near‐field optical microscope and a dedicated spectrometer was realized. The set‐up allows the optical investigation of samples at temperatures from 10 to 300 K. The sample positioning range is as large as 5 × 5 × 5 mm3 and the spatial resolution is in the range of 1.5 µm in the far‐field optical microscopy mode at low temperatures. In the scanning near‐field optical microscope mode the resolution is defined by the microfabricated cantilever probe, which is placed in the focus of a double‐mirror objective. The tip‐to‐sample distance in the scanning near‐field optical microscope is controlled by a beam deflection system in dynamic scanning force microscopy mode. After a description of the apparatus, scanning force topography images of self‐assembled InAs quantum dots on a GaAs substrate with a density of less than one dot per square micrometre are shown, followed by the first spectroscopic investigations of such a sample. The presented results demonstrate the potential of the system.