Tapered nanofiber trapping of high-refractive-index nanoparticles

Abstract

A nanofiber-based optical tweezer is demonstrated. Trapping is achieved by combining attractive near-field optical gradient forces with repulsive electrostatic forces. Silica-coated Fe${}_2$O${}_3$ nanospheres of 300 diameter are trapped as close as 50 nm away from the surface with 810 $\mu$W of optical power, with a maximum trap stiffness of 2.7 pN $\mu$m${}^{-1}$. Electrostatic trapping forces up to 0.5 pN are achieved, a factor of 50 larger than those achievable for the same optical power in conventional optical tweezers. Efficient collection of the optical field directly into the nanofiber enables ultra-sensitive tracking of nanoparticle motion and extraction of its characteristic Brownian motion spectrum, with a minimum position sensitivity of 3.4 $\mathring{A}/\sqrt{\text{Hz}}$.

4 pages and 3 figures

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