High-efficiency and high-resolution fiber-optic probes for near field imaging and spectroscopy

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Abstract
We demonstrate that fiber-optic probes with an intermediate section followed by a rapidly tapering tip lead to transmission efficiency enhancement of better than four orders-of-magnitude at 60 nm tip diameter and more than five orders-of-magnitude at smaller than 40 nm tip diameter over typical taffy-pulled fiber probes. Our highest resolution probes have a tip diameter of 30 nm with a transmission efficiency of 0.02%, and as an example we image tobacco mosaic virus with a resolution better than 35 nm. The probes are made in a two-step process involving pulling and then etching that permits both high efficiency and control of the mechanical resonance properties. The efficiency is enhanced by reducing the distance that the electromagnetic mode travels in the cut-off mode of the fiber probe. The higher resolution is achieved because sharper tips can be made through the etching process.