Figure 1

(Color) (a) Geometry of a nanosystem, initial excitation dipole, and its oscillation wave form. The nanosystem as a thin nanostructured silver film is depicted in blue. A position of the oscillating dipole that initially excites the system is indicated by a double red arrow, and its oscillation in time is shown by a bold red wave form. (b) Field in the far-field zone that is generated by the system following the excitation by the local oscillating dipole: the vector $\left\{E_x\left(t\right),E_z\left(t\right)\right\}$ is shown as a function of the observation time $t$. The color corresponds to the instantaneous ellipticity as explained in the text in connection with the figure. (c) Same as in panel (b), but for a time-reversed pulse in the far zone that is used as an excitation pulse to drive the optical energy nanolocalization at the position of the initial dipole.Reuse & Permissions

Figure 2

(Color) Schematic of plasmonic-nanosystem geometry, local fields, and pulses generated in the far field. Central inset: The geometry of a nanosystem is shown by dark gray, and the local fields in the region surrounding it are shown by colors. The highest local field intensity is depicted by red, and the lowest intensity is indicated by blue (in the rainbow sequence of colors). $A-H$: the excitation wave forms in the far fields obtained as described in the text by positioning the initial excitation dipole at the metal surface at the locations indicated by the corresponding lines. Coordinate vectors $\mathit{\rho }$ of points $A-H$ in the $xz$ plane are (in nm) ${\mathit{\rho }}_A=\left(11,22\right)$, ${\mathit{\rho }}_B=\left(7,16\right)$, ${\mathit{\rho }}_C=\left(7,14\right)$, ${\mathit{\rho }}_D=\left(7,10\right)$, ${\mathit{\rho }}_E=\left(9,7\right)$, ${\mathit{\rho }}_F=\left(18,7\right)$, ${\mathit{\rho }}_G=\left(20,9\right)$, and ${\mathit{\rho }}_H=\left(24,11\right)$. The instantaneous degree of linear polarization $\epsilon$ is calculated as the eccentricity of an instantaneous ellipse found from a fit to a curve formed by the vector $\left\{E_x\left(t\right),E_y\left(t\right)\right\}$ during an instantaneous optical period. The pure circular polarization corresponds to $\epsilon =0$ and is denoted by blue-violet color; the pure linear polarization is for $\epsilon =1$ indicated by red. The corresponding polarization color-coding bar is shown at the left edge of the figure.Reuse & Permissions

Figure 3

(Color online) Spatial distributions of optical excitation at the surface of the nanosystem. These distributions are not normalized in any special way, so that only the distribution form within one panel is informative; the relative magnitudes between the panels depend on the intensity of the excitation and are arbitrary. (a) Distribution of averaged two-photon excitation rate $⟨I^2\left(\mathbf{r}\right)⟩$ for the linear $x$-polarization of the excitation pulse $E$. (b) The same as panel (a), but for the linear $z$-polarization. (c) The two-photon distribution $⟨I^2\left(\mathbf{r}\right)⟩$ for the full polarization shaped ($xz$ polarization) excitation pulse $E$. (d) The same as panel (c), but for the distribution of the instantaneous local field intensity $I\left(t\right)$ for the instance $t=228\text{fs}$ when the intensity at the targeted site reaches its maximum. (e)–(h) The same as panels (a)–(d), but for the excitation pulse $H$.Reuse & Permissions

Figure 4

(Color online) Spatial distributions of the local optical field intensities at the surface of the metal nanostructure. Panels (a)–(h) correspond to the excitation with pulses $A-H$. Each such a distribution is displayed for the instance $t$ at which the intensity for a given panel reaches its global maximum in space and time. This time $t$ is displayed at the top of the corresponding panels. The corresponding targeted sites are indicated by arrows and labeled by the corresponding letters $A-H$ and the coordinates $\left(x,z\right)$. No special normalization has been applied so the distribution within any given panel is informative, but not necessarily the magnitudes of the intensities between the panels. Panels (e) and (h), which were already shown in Fig. 3 as panels (d) and (h), are given also here for the sake of completeness and convenience.Reuse & Permissions

Figure 5

(a)–(h) Temporal dynamics of the local field Intensity $I\left(\mathbf{r},t\right)={\mathbf{E}}^2\left(\mathbf{r},t\right)$ at the corresponding hot spots $A-H$. The down-arrows mark the target time $t=228\text{fs}$ where the local energy concentration is expected to occur.Reuse & Permissions

Figure 6

(Color online) Spatial distributions of the time-averaged mean-squared intensity $⟨I^2\left(\mathbf{r}\right)⟩$. This represents, in particular, the spatial distribution of the two-photon excited photocurrent density. Panels (a)–(h) correspond to the excitation with pulses $A-H$. The corresponding targeted sites are indicated by arrows and labeled by the corresponding letters $A-H$ and coordinates $\left(x,z\right)$. No special normalization has been applied so the distribution within any given panel is informative, but not necessarily the magnitudes of the intensities between the panels. Panels (e) and (h), which were already shown in Fig. 3 as panels (c) and (g), are given also here for the sake of completeness and convenience.Reuse & Permissions