Propagation of femtosecond optical pulses through uncoated and metal-coated near-field fiber probes

The spatiotemporal evolution of a 10-femtosecond light pulse (lambda=805 nm) propagating through uncoated and metal-coated near-field fiber probes is analyzed theoretically within a two-dimensional model for s and p polarization of the incident field. Internal reflection inside uncoated fiber probes (cone angle of 28 degrees) results in an efficient guiding towards the, fiber tip and a diffraction-limited spatial resolution of about 260 nm approximate to lambda/3 in case of s polarization. While the transmission through uncoated fiber probes has negligible effects on the temporal and spectral pulse profile, strong modifications are observed for metal-coated aperture probes. The wavelength-dependent aperture transmission gives rise to a pronounced blueshift and spectral narrowing of the transmitted pulses. (C) 2000 American Institute of Physics. [S0003-6951(00)05023-3].