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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. Leitenstorfer Lehrstuhl für Moderne Optik und Quantenelektronik, Univ. Konstanz

Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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Page 1: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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

Page 2: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

- 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

Page 3: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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 l

Nonlinear 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)

Page 4: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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.

Page 5: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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

Page 6: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

T. Hanke, R. Bratschitsch, A. Leitenstorfer @ Univ. Konstanz, Germany (2011).

THG mapping of particle plasmons

Page 7: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

THG intensity for particle plasmons

Lowest antenna volume gives highest THG intensity !?

Page 8: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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…

Page 9: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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

Page 10: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

rod ellipsoid disc bowtie cross0

0.1

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0.5

0.6

0.7

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0.9

1x-poly-pol

rod ellipsoid disc bowtie cross0

0.1

0.2

0.3

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0.5

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0.7

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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…

Page 11: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

THG autocorrelation

Autocorrelation allows to measure dephasing time of particle plasmons

THG autocorrelation intensity depends on time delay between femtosecond pulses

Page 12: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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

Page 13: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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 oscillation

Knowledge of the plasmon damping time alone suffices to predict the nonlinear intensity !

Page 14: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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!

Page 15: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

THG intensity vs. plasmon dephasing

THG intensity directly scales with plasmon dephasing ! Long dephasing times correspond to large THG intensities

Page 16: Third harmonic imaging of plasmonic nanoantennas Andreas Trügler, Ulrich Hohenester Karl-Franzens-Universität Graz, Austria Work performed together with:

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!