Post on 24-Feb-2016
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Third harmonic imaging of plasmonic nanoantennas
Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria
Work performed together with:
T. Hanke, J. Cesar, R. Bratschitsch, A. LeitenstorferLehrstuhl für Moderne Optik und Quantenelektronik, Univ. Konstanz
- Optical antennas, experiments
- Simulation of metallic nanoparticles
- THG mapping of particle plasmons
Goal of this work
Tailoring spatiotemporal light confinement
in single nanoantennas…
Agenda
200 nm
200 nm
Strong χ(3) nonlinearity for gold,see T. Hanke et al., PRL 103, 257404 (2009)
Nanoantennas as nonlinear emitters
Linear optics: Resolution given by wavelength lNonlinear optics (THG): Resolution given by l / 3
Excitation vs. Detection: Wavelength difference
Hyper-Rayleigh scattering at surface imperfections,see M. Stockman et al., PRL 92, 057402 (2004)
THG
THG intensity ~ | E |6
Pump laser pulse0.97 eV, 24 fs
E
Array of nanoantennas
Subs
trat
e
See S. Kim et al., High-harmonic generation by resonant plasmon field enhancement, Nat. Lett. (2008);T. Hanke, R. Bratschitsch, A. Leitenstorfer @ Univ. Konstanz, Germany (2011).
Imaging with optical antennas
By scanning the excitation spot over the sample and observing the THG signal (in the farfield), we obtain a map of the electric fields of the particle plasmons.
3rd root (THG intensity)
log (THG intensity)
0 20 40 60 80
0 5 10
Third harmonic generation (THG) map (left) and sample (right)
THG mapping of particle plasmons
T. Hanke, R. Bratschitsch, A. Leitenstorfer @ Univ. Konstanz, Germany (2011).
Excitation with fs – pulses and with a bandpass filter for wavelengths 1100 – 1500 nm
T. Hanke, R. Bratschitsch, A. Leitenstorfer @ Univ. Konstanz, Germany (2011).
THG mapping of particle plasmons
THG intensity for particle plasmons
Lowest antenna volume gives highest THG intensity !?
Boundary element method (BEM)
Discretization of surface integral into „boundary elements“Collocation method … surface charges located at centers of boundary elements
F. J. García de Abajo et al., PRB 65, 115418 (2002); U. Hohenester et al., PRB 72, 195429 (2005).
from boundary conditions…
THG mapping of particle plasmons
Size of each triangle ca. 300 nm, discretisation with 20.000 surface elements
Simulation of antenna structures
Result from experiment
rod ellipsoid disc bowtie cross0
0.10.20.30.40.50.60.70.80.9
1x-poly-pol
rod ellipsoid disc bowtie cross0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1x-poly-pol
THG intensity for particle plasmons
Incoherent optics: Biggest volume gives highest intensity…
Coherent optics: Lowest volumes gives highest intensity…
Lowest antenna volume gives highest THG intensity !?
Scattering intensity generated by electromagnetic fields at the surface…
THG autocorrelation
Autocorrelation allows to measure dephasing time of particle plasmons
THG autocorrelation intensity depends on time delay between femtosecond pulses
THG autocorrelation
Autocorrelation allows to measure dephasing time of particle plasmons
THG autocorrelation intensity depends on time delay between femtosecond pulses
harmonic fieldsInsert harmonic fields together with plasmon damping time:
dampingtwo interacting pulses
in / out of phase ratio gives 32:1
THG autocorrelation
Autocorrelation allows to measure dephasing time of particle plasmons
THG autocorrelation intensity depends on time delay between femtosecond pulses
Dephasing times:
rod 5.5 fs ellipse 3.5 fs disc 2.0 fs
Weak plasmon damping effective build-up of the plasmon oscillationKnowledge of the plasmon damping time alone suffices to predict the nonlinear intensity !
30 47 64 81 98 115 132 149 166 183 200
rod length: 300 nmgap: 50 nm
THG intensity vs. plasmon dephasing
THG intensity directly scales with plasmon dephasing ! Long dephasing times correspond to large THG intensities
high nonlinear emission connected to small antenna volumes
radiative damping!
THG intensity vs. plasmon dephasing
THG intensity directly scales with plasmon dephasing ! Long dephasing times correspond to large THG intensities
Summary & Acknowledgement
Temporal scale: Measuring few-fs plasmon damping timesSpatial scale: Mapping of third-harmonic emission
Radiative damping: Lowest volumes generates strongest third-harmonic emission
Ulrich HohenesterJürgen Waxenegger
KFU Graz, Austria
Theoretical Nanoscience
Alfred LeitenstorferRudolf BratschitschTobias HankeVanessa KnittelJulijan Cesar
Moderne Optik und Quantenelektronik
High intensity linked to smallest antenna volume!