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We present a method for the remote generation of a transient near-field probe using conventional IR microscopy optics. Photo-induced reflectivity generated by picosecond pulses of visible light incident on the surface of a semiconductor substrate is used to create transient mirrors with dimensions determined by the spot size of the visible light. The IR light scattered by such sub-wavelength-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 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. |
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