The construction, modeling, and performance characteristics of a new resonator design for ultrafast cavity-dumped oscillators are presented. An acousto-optic Bragg cell was incorporated at the end of the longer arm of a Ti:sapphire oscillator rather than in the shorter arm as in several recent studies. The new arrangement improves the pulse intensity stability of the oscillator and significantly reduces the effort required in construction. The experimental findings are supported by comparison of the stability regions of the laser cavities based on the two different designs. To demonstrate the potential of cavity-dumped oscillators for spatially resolved ultrafast spectroscopy studies, the pulse duration is characterized at the focal plane of two achromatic high-N.A. oil-immersion objectives with different amounts of flat-field correction. Transform-limited pulse widths as short as 15 fs are obtained. To our knowledge, this is the shortest pulse duration measured with true high-N.A. (N.A. > 1) focusing conditions.

An approach to image localized and propagating surface plasmon ͑SP͒ modes is introduced. It is shown that scanning tunneling microscope ͑STM͒-electroluminescence, the radiative decay of SPs induced by inelastically tunneling electrons, observed in Fourier space yields distinct features that reflect the degree of delocalization and spatial distribution of SP modes. The propagating SP is isolated from the localized mode by way of this Fourier space imaging approach. Furthermore, a cylindrically symmetric spatial interference pattern is obtained when the STM-induced plasmon is created within a circular ''corral'' boundary condition.

We present a novel time-domain experimental approach to the study of the dynamics of surface electromagnetic wave propagation in a two-dimensional photonic crystal. A surface plasmon polariton is launched by ultrafast laser pulses and propagates into a photonic crystal, the dynamics of which are measured by an interferometric cross-correlation method. Plasmon photonic stopgaps are characterized by a single measurement. The dispersion around the stopgaps is determined with a series of angle-resolved measurements. Photonic crystal structures, which typically consist of materials with periodically varying dielectric properties, 1 -3 show great promise for use in the manipulation of light to an unprecedented degree. If the Bragg condition is fulf illed, photonic bandgaps can be created. A photonic bandgap in all propagation directions would prohibit even spontaneous emission of an atom inside a photonic crystal.

The photon emission yield observed in scanning tunneling microscopy (STM) measurements of Au hemispheroid-decorated thin films is used to elucidate the interaction of tunneling electrons with local surface plasmon modes. The photon emission probability is found to depend on the surface feature size. The agreement of a model calculation with the experimental results demonstrates that inelastic electron tunneling is the dominant mechanism of STM-induced plasmon excitation for 10–60 nm size metallic features.

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