Deterministic spatiotemporal control of optical fields in nanoantennas and plasmonic circuits

Abstract

We show that pulse shaping techniques can be applied to tailor the ultrafast temporal response of the strongly confined and enhanced optical near fields in the feed gap of resonant optical antennas (ROAs). Using finite-difference time-domain (FDTD) simulations followed by Fourier transformation, we obtain the impulse response of a nano structure in the frequency domain, which allows obtaining its temporal response to any arbitrary pulse shape. We apply the method to achieve deterministic optimal temporal field compression in ROAs with reduced symmetry and in a twowire transmission line connected to a symmetric dipole antenna. The method described here will be of importance for experiments involving coherent control of field propagation in nanophotonic structures and of light-induced processes in nanometer scale volumes.PACS numbers: 73.21, 84.40.Ba, 84.40.Az Resonant optical antennas (ROA) are metal nano structures that upon illumination with light of welldefined wavelength and polarization exhibit hot spots in which the local optical field is spatially confined and strongly enhanced due to geometry-dependent plasmon resonances [1,2]. When excited by a pulsed laser such hot spots provide the possibility to e.g. investigate nonlinear behavior of materials at moderate pulse energies [2,3,4]. Vice versa, well designed ROAs are able to enhance and direct the radiation of point-like sources that drive the antenna from within a hot spot [5,6] thus providing the basis for enhanced single photon sources [5] and antenna-enhanced local spectroscopy [7]. An important future application of ROAs is coherent spatiotemporal control of optical fields for antenna-enhanced local spectroscopies. Coherent control of near-fields by amplitude and polarization pulse shaping has recently been theoretically proposed [8,9,10,11] and experimentally realized [12]. In extension of such experiments it is envisaged to perform spectroscopy of complex matter in contact with a ROA assembly, which will allow studying ultrafast temporal dynamics with nanoscale spatial resolution [13]. The well-established techniques of femtosecond quantum control [14,15] can be realized on the nanoscale. To reach this goal it is important to understand how the resonant character of nano antennas affects the pulse shape in the feed gap and which degrees of freedom are available to be exploited for coherent control of their near-fields. So far efficient ROAs have been realized using noble metal nano rods which are produced by microfabrication techniques. The plasmon resonances of individual rods are determined by their dimensions and dielectric function [16] or equivalently by length-dependent FabryPerot resonances of a plasmon wave [17] propagating with an effective wavelength [18] along the rod and being reflected at its ends. While a single rod may be considered a monopole antenna [6], dipole antennas are formed by aligning two nano rods end to end thus creating a very small feed gap between the two rods where optical fields are concentrated [2]. The plasmon ...

Mode Imaging and Selection in Strongly Coupled Nanoantennas

“…Fig. 3 displays the calculated near-field intensity spectra, which have been normalized with the source spectrum used in the simulation in order to reveal the impulse response [5], i.e. the source-independent antenna response.…”

“…Characterization and well-defined excitation of such eigenmodes is important in order to achieve welldefined functionality in devices [2,3] and to successfully apply techniques of coherent control [4][5][6][7]. Nanoantennas consisting of two strongly coupled particles can serve as a model system to study the impact of mode selectivity [6,8,9].…”

Plasmonic mode converter for controlling optical impedance and nanoscale light-matter interaction

“…Recently, prototype nanocircuits using gap nanoantennas [5,6] in connection with plasmonic two-wire transmission lines (TWTLs) have been theoretically proposed [7][8][9] and experimentally studied [10][11][12], showing a realizable approach to the manipulation of electromagnetic field for enhanced spectroscopy [13,14].…”

Spatiotemporal Ultrafast-Plasmon Control Based on Response Functions of Nanostructures Measured by Interferometric Cross-Correlation Microscopy

“…We hereby apply a new characterization method of ultrafast plasmon: electrical-field cross-correlation imaging using femtosecond laser dark-field microscopy. We set our research goal at spatiotemporal control of plasmon generated by ultra-broadband laser pulses, which are shaped based on the plasmon response function [3] measured with our novel method.…”