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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

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Andreas Trügler , Ulrich Hohenester Karl-Franzens-Universität Graz, Austria. Third harmonic imaging of plasmonic nanoantennas. Work performed together with : T. Hanke, J. Cesar, R. Bratschitsch , A. Leitenstorfer Lehrstuhl für Moderne Optik und Quantenelektronik, Univ. Konstanz. - PowerPoint PPT Presentation

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Page 1: Third harmonic imaging of  plasmonic nanoantennas

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

- 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

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)

Page 4: Third harmonic imaging of  plasmonic nanoantennas

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

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

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

THG mapping of particle plasmons

Page 7: Third harmonic imaging of  plasmonic nanoantennas

THG intensity for particle plasmons

Lowest antenna volume gives highest THG intensity !?

Page 8: Third harmonic imaging of  plasmonic nanoantennas

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

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

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…

Page 11: Third harmonic imaging of  plasmonic nanoantennas

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

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

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 !

Page 14: Third harmonic imaging of  plasmonic nanoantennas

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

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

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!