Aurélien Cuche, Oriane Mollet, Aurélien Drezet & Serge Huant

Néel Institute

CNRS & Univ. Joseph Fourier

Grenoble, France

Towards “Deterministic” quantum plasmonics

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Scanning plasmonics with a nanodiamond: principle

Excitation

Fluorescent nanodiamond (20 nm; NV color-center)

Optical tip in the near-field

Au film •  MAIN GOAL: Play around with surface plasmons in the quantum optics playground.

•  Some previous related works: Akimov et al., Nature (2007). Kolesov et al., Nat. Phys. (2009).

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Why diamond ? •  Contains NV (Nitrogen-Vacancy) color-centers.

•  Intense fluorescence in the red upon blue-green excitation at room temperature.

•  Exceptional photostability : no blinking, no bleaching : “Diamonds are Forever!”

•  A single NV center is a single-photon emitter.

•  Can be produced as fluorescent nanoparticles of size down to 5 nm.

•  Our nanodiamonds:   Mean size 25 nm.   Host 2 NV centers on average.   Have a surface negative charge.

Grafting a selected nanodiamond onto an optical tip (I) The process takes place entirely on a single optical setup (a near-field scanning

optical microscope: NSOM) during scanning.

Etched fiber-tip coated w i t h a p o s i t i v e l y -charged polymer.

To detector

Selected diamond

N e g a t i v e l y - c h a r g e d diamonds (≈ 20 nm) dispersed on a cover slip.

Excitation @ 488nm

50 nm

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Grafting a selected nanodiamond onto an optical tip (II)

Topography Fluorescence

ZOOM ON A TRAPPING EVENT

Scan direction(s)

Here !

Grafting a selected nanodiamond onto an optical tip (III)

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Photon-correlation single NV-center

The nanodiamond-based tip is a single-photon tip.

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Characterization of the functionalized tip

g(2)

(τ)

0 delay τ (ns)

Y. Sonnefraud et al., Opt. Lett. 33, 611 (2008); A. Cuche et al., Opt. Express 17, 19969 (2009).

Spectrum neutral NV0 -center

ZPL

Reference spectrum

Photon intensity-time correlation measurements

Hanbury-Brown & Twiss correlator (1958).

Start-stop system: start initiated by detection event on one detector, stop when second detector detects one photon delays recorded to build a delay histogram. second-order correlation function g2(τ).

Correlator

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g2(τ) =P t +τ t( )P t( )

=1− e− r+Γ( )τ

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gN2 (0) =1− 1

N•  If N emitters:

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g2(0) = 0

NSOM

•  Second-order ( in tensi ty- t ime) correlation function of a quantum emitter:

(r= pumping rate, Γ= radiative decay rate)

•  dip at zero delay, i.e., photon antibunching.

Delay τ (ns)

2

1

0

Y(µm

)

210 X (µm)

50403020100Topographie (nm)

210

40302010Optique (kcps)

1.5

1.0

0.5

0.0

-0.5

g (2)(t)

100500-50Retard t (ns)

160

140

120

100

80

60

40

20

0

C(t)

Diagramme de corrélation

2

1

0

Y(µm

)

210 X (µm)

50403020100Topographie (nm)

210

40302010Optique (kcps)

1.5

1.0

0.5

0.0

-0.5

g (2)(t)

100500-50Retard t (ns)

160

140

120

100

80

60

40

20

0

C(t)

Diagramme de corrélation

•  SPs = Hybrid electron-photon modes propagating at a dielectric /metal interface.

•  SP dispersion relation :

•  But

 “Far-field” photons don’t have enough in-plane momentum to

excite SPs.

GO TO THE NEAR-FIELD

Surface-plasmons (SPs): some reminders

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Re kSP( ) >ωc

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k// SP Au/Air

kmissing

Dielectric (Air, SiO2) εd

k//

k SP

+ + + +- - - - - Metal (Au ...) εm

Evanescent sector

Re(kSP)

Propagating waves (far-field)

•  The Glass line and the SP dispersion curve overlap.

•  For SPs in a thin Au film on glass, conservation of in-plane wavevector “leakage” of SPs into glass at fixed with

Note: at the air/glass interface and for gold in the emission band of NVs.

•  Leakage Radiation Microscopy (LRM) detects these leaky waves without perturbing them for film thicknesses > than skin depth.

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nglass sin θLR( ) ≈ λ2π Re kSP( )

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θLR

Light line

Re(kSP)

Surface-plasmon leakage into glass

« Glass » line

SP Au/Air

KSP

Total Internal Reflection in glass

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θC = 42°

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43° ≤θLR ≤ 45°

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SP

SiO2

Au

θC θLR

d > skin depth

Fourier Filter (removable)

L1

NSOM tip

NA=1.4

Optical Filter

L3 CCD

SPP

NSOM Fourier plane

NSOM Image plane

F1 F1

Leakage radiation microscopy: LRM

DIRECT plane image or

FOURIER plane image

L2 (removable)

See: A. Drezet et al., APL 89, 091117 (2006)

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LRM on a 60 nm gold film with a standard tip ALL IMAGES ON A CCD WITH TIP IN NEAR-FIELD

Standard 100 nm aperture tip. λ = 647 nm

F= Fourier Filtered U = Unfiltered

(a) (b) Image plane Fourier plane

10 µm F

U

U

Checked: surface-plasmon “explosion” shows up when the tip is in the near-field only, not in the far-field (nor in front of the glass substrate).

Two-lobed SP circle of radius :

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δk = Re kSP[ ]

Fourier filter

Propagation length :

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LSP = 2Im kSP[ ]( )−1≈15µm

See B. Hecht et al., PRL 77, 1889 (1996)

Confocal fluorescence

NSOM delay τ [ns] -50 +50 0

0

0.5

1

g(2)(0)= 0.5 2 NV centres

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Y. Sonnefraud et al., Opt. Lett. 33, 611 (2008); A. Cuche et al., Opt. Express 17, 19969 (2009).

Manufacturing the plasmon launcher 2nd order time-intensity correlation

600 650 700 λ [nm]

NV0

Fluorescence spectrum

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LRM on a 60 nm gold film with a 2 NV-center tip ALL IMAGES ON A CCD WITH TIP IN NEAR-FIELD

(c) (d)

2 NV-center tip (1 single nano-diamond).

F

U

U10 µm

Image plane Fourier plane

10 µm F

U

U

Standard 100 nm aperture tip. λ = 647 nm

F= Fourier Filtered U = Unfiltered

(a) (b)

SP circle !!

Note: NV-center tip is that of previous slide

UFourier filter

UF

1.8 µm

Opaque (200 nm) Au film 50 µm fibre → 800 nm

365 µm fibre → 6 µm

Scanning quantum plasmonics (I)

NSOM

X 60, NA=0.95 SPP

APD

Multimode Fiber

NSOM Image plane

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50 µm fibre

365 µm fibre

Simulation

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Scanning quantum plasmonics (II) SP Launcher: 2 NV-centre tip (a different one as previously)

Detection @ 488 nm Detection in the NV emission band

Detection of the “short-range” near-field essentially with intensity scaling like 1/r6.

Detection of the “long-range” plasmon field as well with intensity scaling like 1/r exp(-r/LSP).

be

A. Cuche, O. Mollet, A. Drezet, S. Huant, Nano Lett. 10, 4566 (2010)

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Summary

We have grafted single nanodiamonds hosting two NV centers onto the apex of optical tips for the purpose of :

“DETERMINISTIC“ LAUNCHING OF SINGLE SURFACE PLASMONS

INTO GOLD FILM (at most two at any time).

This is a successful step into

“DETERMINISTIC” QUANTUM PLASMONICS.

THANKS TO:

•  Aurélien Cuche, Oriane Mollet, Aurélien Drezet (Néel Institute).

•  Jean-François Roch, François Treussart (LPQM, ENS Cachan).

•  J.-P. Boudou (LMSSMat, Centrale Paris) & T. Sauvage (CEMHTI, Orléans).

•  Yannick Sonnefraud (Imperial College, London).

€€€€€: ANR Projects NAPHO and PlasTips, Région Rhône-Alpes

THANK YOU FOR YOUR ATTENTION !

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