Microscopy based on the mid-infrared part of the spectrum provides an approach to imaging with a chemically selective contrast mechanism. However, the long wavelength of the mid-IR radiation diffraction limits the spatial resolution to no better than a few microns in conventional IR microscopy. (In practice, commercial IR microscopes rarely do as well as 10 microns). This resolution prevents IR spectroscopy of single sub-cellular or even cellular features routinely observable with conventional visible light microscopes. In this paper we present a technique using conventional IR optics and no near- field tips which enables IR imaging with the resolution of a visible microscope. Photo-induced reflectivity generated by ps pulses of visible light incident on the surface of semiconductor is used to create a transient mirror with dimensions determined by the spot size of the visible light. The IR light scattered by such subwavelength-size mirror is collected after propagating through the sample. As the sample is located on the semiconductor substrate, no near-field distance control is required, and the image can be taken at the speed of a typical laser scanning microscope. And 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 resolution of such an IR microscope is determined by the dimensions of the transient mirror, i.e. by the spot size of the visible light and its penetration depth into the substrate. To prevent resolution degradation due to diffusion of the photo-excited carriers in the substrate, the probe (IR) pulse duration should not exceed a few tens of picoseconds. Preliminary results, prospects and limitations are discussed.
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