Sub-micron resolution "chemical" images of biological systems obtained through use of the intrinsic contrast parameters of molecules - their mid-infrared vibrational modes -are beginning to play an important role in research. Because the wavelengths in the region of interest are typically several microns, such high resolution images can only be obtained through the use of near-field techniques. To date, such techniques have relied upon some form of mechanical probe or tip made with sub-micron dimensions and mechanically scanned across the surface to be imaged while being maintained at a fixed sub-micron distance from the surface. We propose the development of a new approach to near-field microscopy in which imaging is based on a remote, optically generated transient near-field probe. Picosecond pulses of visible light incident on the surface of a semiconductor substrate will produce, through the phenomenon of photo-induced reflectivity, transient mirrors with dimensions determined by the size of the visible beam spot on the substrate. Infrared light scattered by such a sub-wavelength sized mirror will be collected afier propagating through the sample located on the substrate. Since the sample is located on the substrate, no near-field distance control will be required, and images will be available at the rate of conventional laser scanned microscopes. Further, since the near-field probe is generated remotely -using light - the sample to be imaged can be covered by, or encased in, a transparent liquid or solid. The microscope will combine a conventional inverted microscope with an infrared imaging system providing rapid sub-micron imaging simultaneously in the visible and infrared parts of the spectrum. In addition to conventional histologic sections, biological systems, including living cells, will be able to be imaged in liquid media.
