# Thinfilm Hybrid Nanostructures: A Perspective to Subcycle Opto-Electronics and Coherent Control
## 3 Ultrafast Plasmon Modes in Gold-Silica-Silver Sandwiches  
In the following section we present the simulation of time dependent field dynamics in a gold-silica-silver sandwich (Figure 1 driven by a ultrafast laser pulse, with the spectral and temporal properties presented in Figure 2). Figure 3: (**a**) Electric near field at the surface of a 1 nm thick gold disk excited with monochromatic light at 1390 nm and (**b**) the temporal evolution of the integrated field over the left and right half disk after excitation with a broadband pulse together with the excitation signal. From our simulation we retrieve the absorption cross-section of the system shown in Figure 4a. The absorption shows several resonance peaks that can be attributed to different electric field modes, similar to the modes in the gold-silica-gold sandwich we discussed in [24]. The corresponding time averaged electric field of the modes are shown next to the absorption peaks, which can be identified as fundamental TEM 11-TEM 41 modes. According to further simulations, a variation of the phase of the driving electric field results in a significant change of the excited field distribution within the first half-cycle of the driving field presented in Figure 4b. The phase was chosen for the strongest variation in the field pattern for each of the resonances. At 625 nm one oberserves a minimum/maximum (min/max) pair with opposite polarity at 160 deg with respect to the center. Another phase shift of 45 deg shows four alternating min/max pairs. This pattern does not change significantly within another phase shift of 45 deg. The second resonance at 669 nm starts with four min/max pairs at a phase of 160 deg. A phase shift of 45 deg leads to a reduction to only two clear modes in the center of the disk. At the rim of the disk alternating min/max spots become visible driving the build up of a ring mode in the oscillator. Another phase shift of 45 deg leads to a vanishing of the ring mode with three remaining min/max pairs with opposite polarity of the center pair. The third resonance at 753 nm is composed of three alternating min/max pairs, which inverts within a phase shift of 90 deg instead of 180 deg. In the intermediate state only two min/max pairs with the same polarity appear. The outer min/max pair at the rim of the disk shows again a circular modulation but without polarity changes. The fourth resonance at 984 nm features only two min/max pairs that change their polarity within 90 deg. Comparing the different structures one can see the phase dependent excitation of different TEM modes at different resonant wavelength, which already demonstrates the feasibility of time dependent coherent control by tailored light fields. To more closely examine the excitation of whispering gallery modes, we analyse the time dependent field dynamics at two different radii of the top silver disk. Figure 5a,b show the evolution of the plasmonic field along a concentric half circle for radii of 22 nm and 48 nm, respectively. Figure 4: Excitation of surface modes in a gold-silica-silver sandwich. (**a**) The absorption spectrum with the time averaged electric near field of monochromatic excitation; (**b**) shows the evolution of the electric near field at different phase values. For the inner radius of 22 nm in (a) only a regular dipole mode is visible arising with the excitation and changing its polarity consecutively with a sinusoidal superposition resulting in additional intensity modulation of the electric field. The dipole oscillation is decaying exponentially within 60 fs to \(1/e^{2}\). At 90\({}^{\circ}\) the polarization vector of the driving field is perpendicular to the symmetry axis. In the outer ring close to the edge of the disk suddenly after excitation a dipole mode dominates the behaviour up to 40 fs. In the evolution of the field an asymmetric circular ring mode emerges. The circular mode can be figured out by the changing polarity along the line at a constant time step close to 40 fs and 50 fs.