100 femtosecond/100 nanometer near-field probe

Cross-correlation by upconversion has been used to measure pulse widths below 100 fs emitted from an aluminum-coated fiber near-field tip of the variety reported by Betzig et al. [Science 251 (1991) 1468]. The pulses are 0.8 μm center-wavelength with 76 MHz repetition rate generated by a Ti: sapphire mode-locked laser. The size of the probe is estimated at 100 nm by SEM micrographs and previous experience with similar probes used in our continuous wave NSOM systems. We measure average tip output powers of ∼ 1 nW for average input powers of ∼ 500 μW.