Subwavelength direct-write nanopatterning using optically trapped microspheres.
Laser direct-write patterning methods are traditionally limited by the diffraction limit to size scales several hundreds of nanometers at the minimum. In this work, we demonstrate a new method of laser based patterning that overcomes these limitations by taking advantage of near-field enhancement at the surface of dielectric microspheres. Polystyrene microspheres are trapped in CW Bessel beam laser traps above a polyimide surface. A second, pulsed ultraviolet laser gets focused through the bead, and produces nanometer scale features on the substrate. The full width, half maximum of the features generated by this technique is measured and analyzed along with Finite Difference Time Domain simulations to predict the effects of bead size and pulsed laser energy. It is demonstrated that using a 0.76 μm sphere to focus the processing laser results in spots with an average size of 130 nm and a standard deviation of 38 nm, showing that spots with sizes below the diffraction limit can be generated.