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We show experimentally and numerically that Forster-type resonant energy transfer between molecules strongly depends on the interaction with plasmonic resonances in a nearby metallic nanoparticle (MNP). Acceptor luminescence emerges at the expense of donor luminescence when an acceptor molecule harvests the donor's near-field energy. By tuning the resonance of a close-by MNP across the transition energy bands of the molecules, we show how the molecular luminescence is affected and in part even strongly increased.

We report the enhancement of the radiative decay rate of Eu 3+ fluorophores by coupling them to nanoscopic gold disks located on a substrate. When the plasmon resonance frequency of the disks coincides with the fluorophore emission frequency, each disk acts as a supplemental antenna for the fluorophore by converting its nonradiative near field into radiating far field, thereby increasing its radiative decay rate dramatically. The radiative rate is measured by time-correlated single-photon counting for resonant and nonresonant metallic nanodisks. Supplementary theoretical model calculations are found to be in remarkably good agreement with the experiment.

We demonstrate a two-window heterodyne method for measuring the x-p cross correlation, ??(*)(x)? (p)?, of an optical field ? for transverse position x and transverse momentum p. This scheme permits independent control of the x and p resolution. A simple linear transform of the x-p correlation function yields the Wigner phase-space distribution. This technique is useful for both coherent and low-coherence light sources and may permit new biological imaging techniques based on transverse coherence measurement with time gating. We point out an interesting analogy between x-p correlation measurements for classical-wave and quantum fields.

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