Optical Spectroscopy and Laser Desorption on a Nanometer Scale

Optical fiber tips for scanning near-field optical microscopy (SNOM or NSOM) produced by etching with the protection layer method and subsequent metalization show an optical transmission of up to 0.5%. This throughput is 2−4 orders of magnitude higher than that of conventional pulled fiber tips. The high light transmission permits SNOM-based surface analytical and spectroscopic applications with high spatial resolution (<100 nm) and a high chemical information content. Fluorescence imaging of dye-labeled polystyrene spheres is demonstrated. Fast and irreversible photobleaching is shown to take place in the near field with enhanced efficiency. Surface-enhanced Raman spectra of cresol fast violet and p -aminobenzoic acid on a silver substrate are obtained in the optical near field with a signal-to-noise ratio of >10. Rapid heating of chemically etched probes with pulsed laser radiation can be used for thermal desorption of molecules from organic crystals and for modification of polymer surfaces. A lateral resolution of as little as 75 nm fwhm is achieved in the latter experiments.