Multicolor images acquisition by scanning near-field optical microscopy

A multicolor scanning near-field optical microscope (color-SNOM) has been d eveloped to provide real color images of nanoscopic samples for biological and spectroscopical purposes. The sample illumination consists either of a single or a combined beam of different laser wavelengths. A common SNOM set up has been modified in a way that three photomultipliers for blue, green, and red light detection and color separating dichroic filters have been imp lemented. With this beam splitter device, it is possible to acquire simulta neously with the topography three color optical images on three different c hannels. In order to improve the signal-to-noise ratio, etched fiber tips w ith a high transmission intensity were used. Fluorescence experiments on la tex beads labeled with two different dyes and transmission measurements on gold nanoparticles show a wavelength dependent optical contrast. The color- SNOM appears as a powerful tool for high resolution color spectroscopy. (C) 2001 American Institute of Physics.