Femtosecond Optical Trap-Assisted Nanopatterning through Microspheres by a Single Ti:Sapphire Oscillator

A new approach for fabricating a range of patterns using femtosecond optical trap-assisted nanopatterning is presented. We report how a single Gaussian laser beam from a 55 fs, 80 MHz, 780 nm Ti:sapphire oscillator trapping dielectric microspheres near surfaces can be used to enable near-field, direct-write, subwavelength ∼λ/6 (∼130 nm), two-dimensional nanopatterning of a polymer surface. We discuss the stability conditions for effective manipulation of the particle by the pulsed beam. Klein–Kramers and Brownian motion models were used to analyze the positional accuracy of femtosecond tweezers. We studied effects of the microsphere size, pulsed laser energy and light polarization, and spacing between objective focal plane and polymer surface on the pattern size experimentally and theoretically. Microspheres with a diameter of about 1 μm provide the smallest patterns. The experimental results are reasonably matched by generalized Lorentz–Mie theory