Femtosecond phase control of spatial localization of the optical near-field in a metal nanoslit array.

We demonstrate spatial control of optical near-fields by femtosecond phase shaping in one-dimensional plasmonic structures. The near-field images display striking temporal-phase dependence, switching between double- and single-peak images within one lattice constant. The change of the near-field distribution is studied in the time and spectral domain. The spectral composition change observed by varying the time delay between two phase-locked femtosecond pulses explains the spatial control of the near-field images. Modal expansion calculations of linear light transmission using the surface impedance boundary condition are in excellent agreement with experiments.