MELT-DRAWN SCANNING NEAR-FIELD OPTICAL MICROSCOPY PROBE PROFILES

Consistently obtaining super-resolution with scanning near-field optic al microscopy depends almost entirely on the ability to manufacture re producibly probes with aperture sizes smaller than 100 nm. The probe f abrication process usually involves heating an optical fiber using a C O2 laser and melt-drawing the glass to produce a taper. A number of va riables ultimately define the taper shape but the actual effects these parameters have an still not clear. In this work, the physics behind the taper formation is examined in detail for the first time and equat ions describing the initial taper profile and the final aperture size are derived in terms of the experimental conditions. It is shown that the taper shape is primarily determined by the laser spot size. The pu lling force, although important, has a lower significance. Continuum m echanics and Stefan's law are used to show that the aperture size is c losely related to the radius of the fiber at the start of the hard pul l and the fiber temperature at that time. Further comparisons of exper imental data with the expected taper profile exposes the heating effec t of the CO2 laser. Further analysis is given using a form of Mie theo ry which describes the interaction of electromagnetic fields with cyli ndrical structures. These results give many significant insights into the fabrication process and the formation of the aperture. (C) 1996 Am erican Institute of Physics.