Plasmonics is a rapidly developing field at the boundary of physical optics and condensed matter physics. It studies phenomena induced by and associated with surface plasmons-elementary polar excitations bound to surfaces and interfaces of nanostructured good metals. This Roadmap is written collectively by prominent researchers in the field of plasmonics. It encompasses selected aspects of nanoplasmonics. Among them are fundamental aspects such as quantum plasmonics based on quantum-mechanical properties of both underlying materials and plasmons themselves (such as their quantum generator, spaser), plasmonics in novel materials, ultrafast (attosecond) nanoplasmonics, etc. Selected applications of nanoplasmonics are also reflected in this Roadmap, in particular, plasmonic waveguiding, practical applications of plasmonics enabled by novel materials, thermo-plasmonics, plasmonic-induced photochemistry and photo-catalysis. This Roadmap is a concise but authoritative overview of modern plasmonics. It will be of interest to a wide audience of both fundamental physicists and chemists and applied scientists and engineers.

Key words. Fluorescence microscopy, focused ion beam, near-®eld scanning optical microscopy, shear force microscopy, single molecule detection. SummaryThe most dif®cult task in near-®eld scanning optical microscopy (NSOM) is to make a high quality subwavelength aperture probe. Recently, we have developed high de®nition NSOM probes by focused ion beam (FIB) milling. These probes have a higher brightness, better polarization characteristics, better aperture de®nition and a¯atter end face than conventional NSOM probes. We have determined the quality of these probes in four independent ways: by FIB imaging and by shear-force microscopy (both providing geometrical information), by far-®eld optical measurements (yielding throughput and polarization characteristics), and ultimately by single molecule imaging in the near-®eld. In this paper, we report on a new method using shear-force microscopy to study the size of the aperture and the end face of the probe (with a roughness smaller than 1´5 nm).More importantly, we demonstrate the use of single molecules to measure the full three-dimensional optical near-®eld distribution of the probe with molecular spatial resolution. The single molecule images exhibit various intensity patterns, varying from circular and elliptical to double arc and ring structures, which depend on the orientation of the molecules with respect to the probe. The optical resolution in the measurements is not determined by the size of the aperture, but by the high optical ®eld gradients at the rims of the aperture. With a 70 nm aperture probe, we obtain¯uorescence ®eld patterns with 45 nm FWHM. Clearly, this unprecedented near-®eld optical resolution constitutes an order of magnitude improvement over far-®eld methods like confocal microscopy. Focused ion beam etching of NSOM probesMajor improvements in the optical characteristics of aluminium coated NSOM ®bre probes have been accomplished by side-on milling with a focused ion beam (Veerman et al., 1998). This treatment produces a¯at-end face free of aluminium grains with a well-de®ned circularly symmetric aperture. The size of the aperture can be set in a controlled way down to 20 nm. The polarization behaviour of the probes is circularly symmetric with a polarization ratio exceeding 1 : 100. Single molecule¯uorescence signals increase more than one order of magnitude over unmodi®ed probes with the same aperture. With the new probes we could increase the time resolution for monitoring single molecule¯uorescence to 30 ms. For the ®rst time, we have observed real time intersystem crossing of single molecules to the triplet state with NSOM (results will be published elsewhere).A high-resolution image of the probe can be made with the FIB apparatus by detecting secondary electrons that are generated while scanning the ion beam. In this way, the size of the aperture and the thickness of the coating can be determined with an accuracy of 5 nm (Veerman et al., 1998). Figure 1 shows two images of FIB-etched probes with apertures of 70 (6 5) nm (a) and 45 (6 5) ...

Photolyase DNA interactions and the annealing of restriction fragment ends are directly visualized with the atomic force microscope (AFM). To be able to interact with proteins, DNA must be loosely bound to the surface. When MgCl2 is used to immobilize DNA to mica, DNA is attached to the surface at distinct sites. The pieces of DNA in between are free to move over the surface and are available for protein interaction. After implementation of a number of instrumental improvements, the molecules can be visualized routinely, under physiological conditions and with molecular resolution. Images are acquired reproducibly without visible damage for at least 30 min, at a scan rate of 2 x 2 microm2/min and a root mean square noise of less than 0.2 nm. Nonspecific photolyase DNA complexes were visualized, showing association, dissociation, and movement of photolyase over the DNA. The latter result suggests a sliding mechanism by which photolyase can scan DNA for damaged sites. The experiments illustrate the potential that AFM presents for modern molecular biology.

We present a simple scheme to determine the diffusion properties of a thin slab of strongly scattering material by measuring the speckle contrast resulting from the transmission of a femtosecond pulse with controlled bandwidth. In contrast with previous methods, our scheme does not require time measurements nor interferometry. It is well adapted to the characterization of samples for pulse shaping, nonlinear excitation through scattering media, and biological imaging.