Low temperature near field spectroscopy and microscopy

A low temperature near field scanning optical microscope has been constructed. Images of InGaAs quantum wires have been obtained at 4.2 K with a resolution < 100 nm (λ/8). Low temperature spectroscopy and images of 270 nm GaAs quantum dots show vertical dependence in both intensity and spectral shape in collection mode operation. The microscope is designed for use in high magnetic fields and top loads into a 1.2 inch cryostat. A pulled optical fiber [1] tip is mounted in a simple and novel lens collection scheme for reflection mode NSOM. Additional side mounted fibers with focusing GRIN lenses are used for detecting the fiber tip resonance, providing independent shear force microscopy.