title: Performance of visible and mid-infrared scattering-type near-field optical microscopes.
abstract: We describe the principles of two scattering-type near-field optical microscopes (s-SNOMs), one operating at 633 nm wavelength, the other at selectable wavelengths in the range 7.3-11.3 micro m, and compare the measurement experience. Both use interferometric detection of scattered radiation, and are therefore capable of amplitude and phase-contrast imaging. In this study both instruments use the same or even identical commercial probe tips, and measure a single, three-component, test sample. Our results show that the imaging process of s-SNOM is wavelength-independent, namely, that the resolution is determined by the properties of the tip only, and that the contrast is given by the complex refractive index of the sample, predictable from a simple, analytical model of tip-sample interaction. A novel, 'edge-darkening' artefact is described which may appear in s-SNOM and that is wavelength-independent.
authors.affiliation: Max-Planck-Institut für Biochemie, 82152 Martinsried, Germany. taubner@biochem.mpg.de
authors.forename: T
authors.initials: T
authors.lastname: Taubner
authors.forename: R
authors.initials: R
authors.lastname: Hillenbrand
authors.forename: F
authors.initials: F
authors.lastname: Keilmann