A COMPACT NEAR-FIELD SCANNING OPTICAL MICROSCOPE

We present a recently constructed near-field scanning optical microsco pe which incorporates improvements over our previous designs. This mic roscope features an ultra-fine mechanical tip/sample approach with con tinuous submicron control over a range of several millimeters. The pie zo-driven 12 mu m x-y scan range is complimented by a generous 4 mm co arse mechanical translation range in each direction. The construction materials used in the feedback loop have been carefully chosen for the rmal compatibility in order to reduce differential expansion and contr action between the tip and sample. A unique pressure-fit sample mounti ng allows for quick and reliable sample exchange. Shear-force feedback light is delivered to the scan head via an optical fiber so that a la ser cf any type may be used as a source. This dither light is collimat ed and refocused onto the tip, delivering a consistently small spot wh ich is collected by a high NA objective. This new scan head incorporat es an optical system which will permit the linearization of scan piezo response similar to a scheme used successfully with AFMs. This is des igned to both overcome the piezo's inherent hysteresis, and also to el iminate drift during long-duration scans or spectroscopy at a single p oint. The scan-head design offers added flexibility due to the use of optical fibers to deliver the dither and scan linearization light, an functions in any orientation for use in conjunction with upright or in verted optical microscopes. (C) 1998 Elsevier Science B.V. All rights reserved.