A Scanning Near-Field Optical Microscope with Optical Distance Control

Abstract

An all optical scanning near-field microscope including vertical distance regulation is described. The probe-sample distance is maintained to within an accuracy of approximately lnm using a profilometer based on the principles of confocal microscopy. The profilometer is incorporated into a system where subwavelength resolution is obtained by scanning with an aperture in a metal-coated tapered optical fibre. The final system will be capable of producing both confocal and the higher resolution near-field images along with an accurate profile of the scanned surface using only optical techniques. Intensity maps of the near-zone fields produced from the cleaved face of an optical fibre are also presented. No other optical technique is capable of directly sensing, with such high resolution, evanescent optical fields. Hence, this method is an invaluable aid in measurements of mode field diameters and the development of optical fibre sensors.