A compact near-field scanning optical microscope

Abstract

We present a recently constructed near-field scanning optical microscope which incorporates improvements over our previous designs. This microscope features an ultra-fine mechanical tip/sample approach with continuous submicron control over a range of several millimeters. The piezo-driven 12 μm x– y scan range is complimented by a generous 4 mm coarse mechanical translation range in each direction. The construction materials used in the feedback loop have been carefully chosen for thermal compatibility in order to reduce differential expansion and contraction between the tip and sample. A unique pressure-fit sample mounting allows for quick and reliable sample exchange. Shear-force feedback light is delivered to the scan head via an optical fiber so that a laser of any type may be used as a source. This dither light is collimated and refocused onto the tip, delivering a consistently small spot which is collected by a high NA objective. This new scan head incorporates an optical system which will permit the linearization of scan piezo response similar to a scheme used successfully with AFMs. This is designed to both overcome the piezo's inherent hysteresis, and also to eliminate drift during long-duration scans or spectroscopy at a single point. The scan-head design offers added flexibility due to the use of optical fibers to deliver the dither and scan linearization light, and functions in any orientation for use in conjunction with upright or inverted optical microscopes.