ETCHED CHALCOGENIDE FIBERS FOR NEAR-FIELD INFRARED SCANNING MICROSCOPY

Typical infrared transmitting fibers comprise a chalcogenide core surr ounded by a sulfur-selenide cladding, which is in turn coated with a p olymer such as polyamide. For use in a near-field scanning infrared mi croscope (NSIM), such infrared-transmitting fibers must be tapered to a sharp point. Sharper points allow smaller apertures, which allow hig her resolution. The light throughput of the probe depends on the lengt h of the taper region: the longer the taper length, the further the in frared radiation must propagate through a waveguide smaller than its w avelength. Thus, shorter taper lengths should give higher light throug hput. We describe a method for etching chalcogenide fibers to submicro n points by simple chemical means. Methods are described for removal o f the polyamide coating, stripping of the SS cladding surrounding the core, and etching the chalcogenide fiber core to a sharp point. Remova l of the polyamide coating is most easily accomplished by dissolution in 4-Chloro-1-butanol, The SSe cladding is removed by soaking the fibe r in 0.1 M NaOH overnight. The chalcogenide core is tapered to a sharp point by immersion in a two-phase etching system, where the top phase is an inert organic solvent, and the bottom phase is a strong oxidant , Fibers both with and without cladding have been tapered. The resulti ng fibers have a taper length on the order of the core diameter, and t erminate with a submicron end radius of curvature. The potential for u se in a NSIM, as well as other uses, is discussed. (C) 1998 American I nstitute of Physics.