Nanolocalized nonlinear electron photoemission under coherent control

Analytic Optimization of Near-Field Optical Chirality Enhancement

We present an analytic derivation for the enhancement of local optical chirality in the near field of plasmonic nanostructures by tuning the far-field polarization of external light. We illustrate the results by means of simulations with an achiral and a chiral nanostructure assembly and demonstrate that local optical chirality is significantly enhanced with respect to circular polarization in free space. The optimal external far-field polarizations are different from both circular and linear. Symmetry properties of the nanostructure can be exploited to determine whether the optimal far-field polarization is circular. Furthermore, the optimal far-field polarization depends on the frequency, which results in complex-shaped laser pulses for broadband optimization.

Observation of Plasmon Wave Packet Motions via Femtosecond Time-Resolved Near-Field Imaging Techniques

The generation and dynamics of plasmon wave packets in single gold nanorods were observed at a spatiotemporal scale of 100 nm and 10 fs via time-resolved near-field optical microscopy. Following simultaneous excitation of two plasmon modes of a nanorod with an ultrashort near-field pulse, a decay and revival feature of the time-resolved signal was obtained, which reflected the reciprocating motion of the wave packet. The time-resolved near-field images were also indicative of the wave packet motion. At some period of time after the excitation, the spatial features of the two modes appeared alternately, showing motion of plasmonic wave crests along the rod. The wave packet propagation was clearly demonstrated from this observation with the aid of a simulation model. The present experimental scheme opens the door to coherent control of plasmon-induced optical fields in a nanometer spatial scale and femtosecond temporal scale.

Spatiotemporal control of temperature in nanostructures heated by coherent laser fields

We demonstrate theoretically that it is possible to exercise coherent control of the temperature in nanostructures by laser fields. In particular we show that by use of nanosecond laser pulses it is possible to induce a temperature distribution on a collection of nanoparticles which can last for up to thousands of nanoseconds before assuming the temperature of the environment. Although the form of the temperature distribution depends on the spatiotemporal control of the optical near field induced by the laser field, it is far from being proportional to the local radiation field at a particular point due to the cooling mechanisms which take place among the nanoparticles. We also show that it is possible to selectively heat a given target nanoparticle with adaptive control of the illuminating laser field without a nanoscale focus.

Near field of strongly coupled plasmons: uncovering dark modes

Strongly coupled plasmons in a system of individual gold nanoparticles placed at subnanometer distance to a gold film (nanoparticle-on-plane, NPOP) are investigated using two complementary single particle spectroscopy techniques. Optical scattering spectroscopy exclusively detects plasmon modes that couple to the far field via their dipole moment (bright modes). By using photoemission electron microscopy (PEEM), we detect in the identical NPOPs near-field modes that do not couple to the scattered far field (dark modes) and are characterized by a strongly enhanced nonlinear electron emission process. To our knowledge, this is the first time that both far- and near-field spectroscopy are carried out for identical individual nanostructures interacting via a subnanometer gap. Strongly resonant electron emission occurs at excitation wavelengths far off-resonant in the scattering spectra.

Plasmon-enhanced sub-wavelength laser ablation: plasmonic nanojets

In response to the incident light's electric field, the electron density oscillates in the plasmonic hotspots producing an electric current. Associated Ohmic losses raise the temperature of the material within the plasmonic hotspot above the melting point. A nanojet and nanosphere ejection can then be observed precisely from the plasmonic hotspots.

Nanoplasmonics: past, present, and glimpse into future

A review of nanoplasmonics is given. This includes fundamentals, nanolocalization of optical energy and hot spots, ultrafast nanoplasmonics and control of the spatiotemporal nanolocalization of optical fields, and quantum nanoplasmonics (spaser and gain-assisted plasmonics). This article reviews both fundamental theoretical ideas in nanoplasmonics and selected experimental developments. It is designed both for specialists in the field and general physics readership.

Gold nanorods 3D-supercrystals as surface enhanced Raman scattering spectroscopy substrates for the rapid detection of scrambled prions

Highly organized supercrystals of Au nanorods with plasmonic antennae enhancement of electrical field have made possible fast direct detection of prions in complex biological media such as serum and blood. The nearly perfect three-dimensional organization of nanorods render these systems excellent surface enhanced Raman scattering spectroscopy substrates with uniform electric field enhancement, leading to reproducibly high enhancement factor in the desirable spectral range.

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.

Toward full spatiotemporal control on the nanoscale

We introduce an approach to implement full coherent control on nanometer length scales. It is based on spatiotemporal modulation of the surface plasmon polariton (SPP) fields at the thick edge of a nanowedge. The SPP wavepackets propagating toward the sharp edge of this nanowedge are compressed and adiabatically concentrated at a nanofocus, forming an ultrashort pulse of local fields. The profile of the focused waveform as a function of time and one spatial dimension is completely coherently controlled.

Localized multiphoton emission of femtosecond electron pulses from metal nanotips

Intense multiphoton electron emission is observed from sharp (approximately 20 nm radius) metallic tips illuminated with weak 100-pJ, 7-fs light pulses. Local field enhancement, evidenced by concurrent nonlinear light generation, confines the emission to the tip apex. Electrons are emitted from a highly excited nonequilibrium carrier distribution, resulting in a marked change of the absolute electron flux and its dependence on optical power with the tip bias voltage. The strong optical nonlinearity of the electron emission allows us to image the local optical field near a metallic nanostructure with a spatial resolution of a few tens of nanometers in a novel tip-enhanced electron emission microscope.

Polarization and phase control of remote surface-plasmon-mediated two-photon-induced emission and waveguiding

We report here on the control of remote surface-plasmon-mediated two-photon-induced luminescence of dendritic silver nanoparticle aggregates as observed by femtosecond laser microscopy. With a focal spot diameter approximately 1 microm, polarized remote emission has been observed 99 microm from the focal spot. We show control over the regions of emission by changing the polarization of the incident beam and by changing the spectral phase of the laser pulse.

Phase and polarization control as a route to plasmonic nanodevices

We extend the concepts of phase, polarization, and feedback control of matter to develop a general approach for guiding light in the nanoscale via nanoparticle arrays. The phase and polarization of the excitation source are first introduced as tools for control over the pathway of light at array intersections. Genetic algorithms are next applied as a systematic design tool, wherein both the excitation field parameters and the structural parameters of the nanoparticle array are optimized to make devices with desired functionality. Implications to research fields such as single molecule spectroscopy, spatially confined chemistry, optical logic, and nanoscale sensing are envisioned.