Melt-drawn scanning near-field optical microscopy probe profiles

Abstract

Consistently obtaining super-resolution with scanning near-field optical microscopy depends almost entirely on the ability to manufacture reproducibly probes with aperture sizes smaller than 100 nm. The probe fabrication process usually involves heating an optical fiber using a CO 2 laser and melt-drawing the glass to produce a taper. A number of variables ultimately define the taper shape but the actual effects these parameters have are still not clear. In this work, the physics behind the taper formation is examined in detail for the first time and equations 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 pulling force, although important, has a lower significance. Continuum mechanics and Stefan's law are used to show that the aperture size is closely related to the radius of the fiber at the start of the hard pull and the fiber temperature at that time. Further comparisons of experimental data with the expected taper profile exposes the heating effect of the CO 2 laser. Further analysis is given using a form of Mie theory which describes the interaction of electromagnetic fields with cylindrical structures. These results give many significant insights into the fabrication process and the formation of the aperture.

Near-Field Scanning Optical Microscopy for High-Resolution Membrane Studies

“…Since the quality of the metal coating is the key metric for NSOM tip performance, this is a major obstacle for the chemical etching approach. For this reason, we find that the heating and pulling method for tip formation remains the best approach for standard NSOM tip fabrication (18, 19). This is the most prevalent approach for fabricating NSOM probes and, in our experience, the easiest method for reproducibly fabricating probes once the proper procedures are in place.…”

“…These parameters enable a large range of taper shapes to be fabricated in fiber optic probes. For example, high heat and hard pulls result in long tapers with very small tip apertures while low heat and soft pulls result in short tapers with larger tip apertures (18, 19). Unfortunately, this approach cannot create short tapers with small apertures, a combination that incorporates efficient light throughput with high spatial resolution.…”

Dynamic electrochemical-etching technique for tungsten tips suitable for multi-tip scanning tunneling microscopes

“…Huge number of works on the fabrication of sharp tips have been performed and several techniques have been developed, such as grinding [2,12], cutting [13][14][15][16], mechanical pulling [17][18][19][20][21][22][23][24][25][26][27], chemical or electrochemical etching , field evaporation or other field-induced methods [72][73][74][75][76], beam deposition [77][78][79][80][81][82][83], ion milling [15,[84][85][86][87][88][89][90][91][92][93][94], and others [95].…”

“…There are also several kinds of methods in the fabrication of fiber probes [12,[17][18][19][20][21][22][23][24][25][26][27][67][68][69][70][71]. Among them, a dynamic etching method has advantages in reliability and controllability of the taper angle of probe apex [69][70][71].…”

Fabricating subwavelength fiber taper using a CO 2 laser

“…The CO 2 laser beam is free of contamination, controllable, fast acting, and free of inertia. And it has been used as a heat source to fabricate fiber taper in previous studies 2,5 . Therefore it can be used as an ideal heating source for controlling the taper shape precisely and fabricating subwavelength fiber tapers.…”