In this
project, we investigate the ultrafast temporal dynamics as well as the
nonlinear optical properties of hybrid plasmonic nanostructures. Our model
system consists of a gold nanowire grating on top of a dielectric slab waveguide.
In the nanowires, we optically excite localized plasmons which oscillate perpendicular
to the wire. Since the dephasing processes of localized particle plasmons occur
on a femtosecond timescale, methods of ultrashort laser pulse characterization (nonlinear
autocorrelation techniques) are used to investigate their temporal dynamics. The
dephasing of particle plasmons can be tailored by coupling them to photonic modes
in the dielectric slab waveguide. In this way, a coupled plasmonic-photonic
system with new eigenstates (waveguide plasmon polariton) and significantly
prolonged dephasing times is excited.
In a further
step, we want to influence the plasmon polariton dephasing dynamically in an
all-optical control experiment. Using a femtosecond laser pulse sequence, the
plasmon polariton polarization, which is excited by a first sub-8 fs laser
pulse, is coherently turned on or off by a second pulse, only a few tens of
femtoseconds after the excitation. To read out the plasmon polariton
polarization, we use a third pulse together with a nonlinear process (third
harmonic generation). The experimental data shows all-optical plasmon control
with high contrast and perfect agreement with numerical calculations [T. Utikal et al., Phys.
Rev. Lett. 104, 113903
(2010)]. This concept might open up a route to ultrafast plasmonic switching on
the nanoscale with femtosecond accuracy.
Additionally, we are interested in the nonlinear optical response of the
hybrid plasmonic structures. From third harmonic generation spectroscopy it is
found that the shape of the nonlinear optical spectra is completely different
when compared with the linear spectra. By carefully varying the structure
geometry as well as the constituent materials, the origin of the nonlinearity
can be unambiguously identified from the shape of the nonlinear spectra. The
observations are confirmed by several theoretical considerations [T. Utikal et al., Phys. Rev.
Lett. 106, 133901 (2011)].
In the future, our concepts will be applied to more complex plasmonic
structures such as plasmonic oligomers [M. Hentschel et al., Nano Lett. 10, 2721 (2010)] and three-dimensional
nanoantennas [D. Drégely et al., Nat.
Communications 2, 267
(2011)].
Publications
Plasmonic oligomers: the role of individual particles in collective behavior
M. Hentschel, D. Dregely, R. Vogelgesang, H. Giessen, and N. Liu
ACS Nano 5 (2011) 2042
We present a comprehensive experimental study of the optical properties of plasmonic oligomers. We show that both the constitution and configuration of plasmonic oligomers have a large influence on their resonant behavior, which draws a compelling analogy to molecular theory in chemistry. To elucidate the constitution influence, we vary the size of individual nanoparticles and identify the role of the target nanoparticle from the spectral change. To illustrate the configuration influence, we vary the positions and numbers of nanoparticles in a plasmonic oligomer. Additionally, we demonstrate experimentally a large spectral redshift at the transition from displaced nanoparticles to touching ones. The oligomeric design strategy opens up a rich pathway for the implementation of optimized optical properties into complex plasmonic nanostructures for specific applications.
Excitation and Tuning of Higher-order Fano Resonances in Plasmonic Oligomer Clusters
D. Dregely, M. Hentschel, and H. Giessen
ACS Nano 5 (2011) 8202
Plasmonic oligomer clusters are assemblies of closely packed metallic nanoparticles. They provide a rich set of spectral features such as Fano lineshapes and a simultaneous tunability of the supported resonances in the optical wavelength regime. In this study, we investigate numerically and experimentally clusters of plasmonic nanoparticles that exhibit multiple Fano resonances due to the interference of one broad superradiant mode and multiple narrow subradiant modes. In particular we investigate oligomers with multiple ring modes and elongated chains of nanoparticles surrounded by one ring of nanoparticles. We show that the number of nanoparticles and their respective arrangement in the cluster strongly influence the spectral position and modulation depth of the spectral signature of the supported modes. Our study opens up the pathway to “plasmonic super molecules” that show unprecedented tunability, which renders them highly suitable for applications such as multiwavelength surface-enhanced Raman scattering.
Nonlinear photonics with metallic nanostructures on top of dielectrics and waveguides
T. Utikal, M. Hentschel, and H. Giessen
Appl. Phys. B 105 (2011) 51
We review recent experimental and theoretical studies of the ultrafast and nonlinear optical response of metallic nanostructures on top of dielectric substrates and slab waveguides where plasmon hybridization is a key ingredient. In a first three-pulse all-optical control experiment a hybrid plasmonic mode is turned on or off only a few tens of femtoseconds after its excitation. A second experiment concentrates on the origin of the nonlinear response in a metallo-dielectric photonic crystal structure. We show that the shape of the nonlinear optical spectra provides unambiguous information about the nonlinear optical contribution of the metallic as well as the dielectric part of the structure. Furthermore, we discuss the influence of slow-light on the nonlinear response. All experimental results agree perfectly with numerical scattering matrix calculations as well as simulations based on a classical harmonic oscillator model.
Tailoring the photonic band splitting in metallo-dielectric photonic crystal superlattices
T. Utikal, T. Zentgraf, S. G. Tikhodeev, M. Lippitz, and H. Giessen
Phys. Rev. B 84 (2011) 075101-1
We experimentally and theoretically investigate the influence of a structured supercell on the band splitting of one-dimensional metallodielectric photonic crystal superlattices. We show that the splitting of the photonic bands can be modified by periodic structuring of the elementary unit cell of the photonic crystal. For our investigation we constructed metallic photonic crystal superlattices by creating supercells from standard photonic crystal building blocks and arranged them at certain distances apart. The optical properties were obtained by conventional angle-resolved white-light transmission measurements.
3D optical Yagi-Uda nanoantenna-array
D. Dregely, R. Taubert, J. Dorfmüller, R. Vogelgesang, K. Kern, and H. Giessen
Nat. Communications 2 (2011) 267
Future photonic circuits with the capability of high-speed data processing at optical frequencies will rely on the implementation of efficient emitters and detectors on the nanoscale. Towards this goal, bridging the size mismatch between optical radiation and subwavelength emitters or detectors by optical nanoantennas is a subject of current research in the field of plasmonics. Here we introduce an array of three-dimensional optical Yagi–Uda antennas, fabricated using top-down fabrication techniques combined with layer-by-layer processing. We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension. Measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity. Moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths.
Towards the origin of the nonlinear response in hybrid plasmonic systems
T. Utikal, T. Zentgraf, T. Paul, C. Rockstuhl, F. Lederer, M. Lippitz, and H. Giessen
Phys. Rev. Lett. 106 (2011) 133901-1
Plasmonic systems are known for their distinct nonlinear optical properties when compared to purely
dielectric materials. Although it is well accepted that the enhanced nonlinear processes in plasmonicdielectric
compounds are related to the excitation of localized plasmon resonances, their exact origin is
concealed by the local field enhancement in the surrounding material and the nonlinearity in the metal.
Here, we show that the origin of third-harmonic generation in hybrid plasmonic-dielectric compounds can
be unambiguously identified from the shape of the nonlinear spectrum.
Tailoring the ultrafast dynamics of optical magnetism in magnetic photonic crystals
M. Geiselmann, T. Utikal, M. Lippitz, and H. Giessen
Phys. Rev. B 81 (2010) 235101-1
We investigate the ultrafast time dynamics of magnetic waveguide-particle-plasmon polaritons in a magnetic photonic crystal. This magnetic mode consists of the antisymmetric localized charge oscillation in metallic cut-wire pairs. At the appropriate periodicity, strong coupling and polaritonic hybridization take place between the antisymmetric plasmon resonance and the excited photonic mode of the underlying slab waveguide. By varying the lattice period and the wire cross section of the structure, tailoring of the temporal dynamics of the magnetic polariton is possible. Simulations are in good agreement with third-order nonlinear autocorrelation function measurements and confirm extremely long dephasing times of the polaritonic system. Future applications could include all-optical control of optical magnetism.
All-optical control of hybridized plasmon polaritons in metallic nanostructures
T. Utikal, M. I. Stockman, A. P. Heberle, M. Lippitz, and H. Giessen
Phys. Rev. Lett. 104 (2010) 113903-1
We demonstrate complete all-optical and phase-stable control of the linear optical polarization and the nonlinear coherent response (third-harmonic generation) of a hybrid nanoplasmonic-photonic system. A few tens of femtoseconds after the excitation, we turn the response on and off at any given point in time and probe its temporal evolution throughout the control process with a three-pulse nonlinear optical technique. After being switched off, the polarization and the nonlinear radiation remain off permanently. All experiments agree well with numerical simulations based on a damped harmonic oscillator model.
Transition from isolated to collective modes in plasmonic oligomers
M. Hentschel, M. Saliba, R. Vogelgesang, H. Giessen, A. P. Alivisatos, and N. Liu
Nano Lett. 10 (2010) 2721
We demonstrate the transition from isolated to collective optical modes in plasmonic oligomers. Specifically, we investigate the resonant behavior of planar plasmonic hexamers and heptamers with gradually decreasing the interparticle gap separation. A pronounced Fano resonance is observed in the plasmonic heptamer for separations smaller than 60 nm. The spectral characteristics change drastically upon removal of the central nanoparticle. Our work paves the road toward complex hierarchical plasmonic oligmers with tailored optical properties.
Ultrafast time-resolved spectroscopy of 1D metal-dielectric photonic crystals
T. Ergin, T. Benkert, H. Giessen, and M. Lippitz
Phys. Rev. B 79 (2009) 245134-1
We study the all-optical switching behavior of one-dimensional metal-dielectric photonic crystals due to the nonlinearity induced by a hot electron gas. A polychromatic pump-probe setup is used to determine the wavelength and pump intensity dependence of the ultrafast transmission suppression as well as the dynamics of the process on a subpicosecond time scale. We find ultrafast (subpicosecond) as well as a slow (millisecond) behavior. We present a model of the ultrafast dynamics and nonlinear response, which can fit the measured data well and allows us to separate the thermal and the electronic response of the system.
