Single photon nano-antennas Learning objectives: - scatterering - emission control Resonant Nanophotonics Annemarie Berkhout Kevin Cognee Hugo Doeleman Beniamino Ferrando Tomas Kaandorp Radoslaw Kolkowski Ruslan Rohrich Isabelle Palstra Tom Wolterink Collaborations Philippe Lalanne Ewold Verhagen Albert Polman Stefan Witte Femius Koenderink – [email protected]Center for Nanophotonics, AMOLF, Amsterdam
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Single photon nano-antennas - AMOLF...2019/06/01 · Single photon sources Quantum information Lozano, Verschuuren, Rivas LED lighting & phosphors Nanophotonics to control emission,
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Single photon nano-antennasLearning objectives:- scatterering- emission control
Nanophotonics to control emission, absorption, lasing…- Directionality, polarization and phasefront of emission- Efficiency, brightness and Purcell factor- Spatial and temporal coherence
2
Making a light source
Space• Whereto does the photon go ?• With what polarization ?
Time• How long does it take for the photon to appear ?
Matter• Selection rules – what color comes out? Engineering wave functions
Engineering light
3
Basic scenarios
Microcavity - barely leaks light- high Q [ stores light ~ 105 optical cycles]- volume encloses a standing wave (l3)
Antenna - excellent radiator - low Q [ looses light in 10 optical cycles]- `antenna gain & directivity’
Orrit, Moerner, Wenger van Hulst, Wenger, AMOLF Greffet Mikkelsen, Baumberg
Why are metal particles extremely strong scatterers?What is an `extremely strong’ scatterer anyway?
How do you generate directivity from a point source?How does emission get accelerated? What determines brightness?What is a good measurement for performance?
6
Scattering & observables
Extinction cross section [m2]
Power removed from beamIncident intensity
Extinction = scattering + absorption
removed from the beam
Re-radiated intoall angles
Lost as heat in the scatterer
7
Scattering figures of meritC
ross
sec
tio
n /
ph
ysic
al a
rea
Physical area
Rayleigh regime: (r/l)4
Resonances create s > pr2
Geometric resonances require size
Diagram: astronomy.stackexchange.com - actual theory: G. Mie, H. C. van de HulstThe diagram is not quite correct – in the geometric limit, you actually find twice the physical cross section (Bohren & Huffman) 8
Diagram: astronomy.stackexchange.com - actual theory: G. Mie, H. C. van de HulstThe diagram is not quite correct – in the geometric limit, you actually find twice the physical cross section (Bohren & Huffman)
Scattering figures of meritC
ross
sec
tio
n /
ph
ysic
al a
rea
Plasmonics
- Deep sub-l size, no geometry-only resonances
- Material resonance ensures largecross section
9
Scattering resonance
Murray & Barnes, Adv Mat 2007
Cross section
>
geometric area
aV Polarizability
> Physical volume
Figures of Merit
2
13
a V
Circa 103-104 free electrons
Incident field separates e- from ionic backbone
Linear restoring force implies a resonance
Resonant dipole scatterers l ~300-1000 nm, Q ~ 5-30
Induced dipoles
E0 m
z
r
q
a
Qualitatively:
Incident field induces local polarization density in the medium
If the object is so small that Ein hardly varies over it ( a << l ), the local induced response adds up to an induced dipole
11
Electrostatic sphere
20203
02
0001
42
2
3
2
r
prE
rEarE
rErErE
mm
m
m
m
m
m
p
qq
q
q
q
q
q
coscos
coscos
coscoscos
E0 m
z
r
q
a
Electrostatic treatment (frequency = 0)Sphere in a homogeneous electric field
Inside sphere: homogeneous field along incident field (Ez)Outside sphere: background field plus field of a dipole
In the ball:
Outside:
Incidentplane wave Ez Scattered, dipole
Check: (1) this potential is itself continuous, yet (2) its derivative jumps by , since Div D=0
• Source brightness [counts/sec] is enhanced because
pump field is concentrated at the emitter
• Given that the source has been excited and emits a photon,
antenna effects redirect the light into a narrow beam
• Fluorescence decay rates are enhanced - Purcell effects on rate and IQE
23
Radiation provides resistance
Radiation resistance – environment sets power to current ratio
The work you need to do keep current j going depends on environment
Conversely, the same current can generate more power (or less)
Dipole above a mirror in classical terms
- +
-+
-
+
-
+
Interference of the dipole field with that of its mirror image The same current radiates a different far field power
25
Backaction view point
-+
In order to maintain constant currentone does work against ones own field
Suppose we call the dipole field
Resistance is due to field Im pT.G(r’,r’).p that comes back to the source“Imaginary part of the Green function”
26
Single quantum emitter
• After one excitation, emits just one quantum of light
• Probabilistic timing of when emission occurs
• Fermi’s Golden rule: exponential decay, characteristic rate [inverse time]
Laser pulses
Hits ondetector
Hits onAPD 2
Time
S0
S1
Time (ns)
Lounis & Orrit, Single photon sources, Rep. Prog. Phys (2005)
Drexhage experiment on single quantum emitter
Note how: the power is not the variable of choice: one photon out per photon in (QE=1)the decay rate varies with mirror-geometry
K.H. Drexhage and many since - ensembles of emitters (1966)Single emitters: Buchler PRL (2005), Frimmer (2013), Huck (2016)
0 40 80t (ns)
10
100
1000
Even
ts
slope
Single NV center in nanodiamond
28
Understanding Fermi’s Golden Rule
2
2all finalstates
2( )f i f i
f
V E Ep
Energy conservationMatrix elements:Transition strengthSelection rules
Spontaneous emission of a two-level atom:
Initial state: excited atom + 0 photons.
Final state: ground state atom + 1 photon in some photon state
Question: how many states are there for the photon ???(constraint: photon energy = atomic energy level difference)
29
How many photon states are there in a box of vacuum ?
( , ) sin( ) with ( , , )i tE x t Ae l m nL
p k r kStates in an LxLxL box:
l,m,n positive integers
Number of states with |k|between k and k+dk:
3
24( ) 2
8
LN k dk k dkp
p
l,m,n > 0fill one octant
fudge 2 for polarization
As a function of frequency (ck):
2 23 3
2 2 2 3( )
dkN d L d L d
c d c
p p
Picture fromhttp://britneyspears.ac
k
dk
30
Fluorescence decay rates
Fermi’s Rule: Fluorescence rate number of photon states
0 2 4 60
50000
100000
150000
Photo
n s
tate
s p
er
m3, per
Hz
Frequency (1015
s-1)
Visible light: ~105 photon states per Hz, per m3 of vacuum
Loudon, The Quantum Theory of Light
Cavity
Fluorescence in a cavity
0 2 4 60
50000
100000
150000
Photo
n s
tate
s p
er
m3, per
Hz
Frequency (1015
s-1)
Fermi’s Rule: Fluorescence rate number of photon states
Microcavity: Exactly one extra state per D=/Q in a volume V
Gérard & Gayral, J. Lightw. Technol. (1999)
Cavity
Fluorescence in a cavity
0 2 4 60
50000
100000
150000
Photo
n s
tate
s p
er
m3, per
Hz
Frequency (1015
s-1)
Fermi’s Rule: Fluorescence rate number of photon states
Microcavity: Exactly one extra state per D=/Q in a volume V
Purcell factor
3
2
3
4
QF
Vl
p
Gérard & Gayral, J. Lightw. Technol. (1999)
From LDOS to actual performance
S0
S1
A unit efficiency emitter, emits exactly a single ħ per pump photonHigh LDOS will make the photon come out faster, but the source is not more bright
A low-efficiency sources gains efficiency by outcompeting nonradiative loss
LDOS itself may contain new loss channels - quenching
nonradiative
34
Antenna achievement chart
Brighter per fluorophore
1000x brighter
Intrinsically poor emitters- 10x boost in QE- 100x boost in pump
Intrinsically good emitters- 500 - 1000x faster- Brighter by pump boost
Directional & faster
Orrit, Moerner, Wenger van Hulst, Wenger, AMOLF Greffet Mikkelsen, Baumberg
Brighter by beaming
Factor ~ 5
35
Doing a good measurement is not easy
• Make sure you have a single emitter (at a time)
• Of known quantum efficiency
• At the right location
• Calibrate collection efficiency, directivity, rate, and efficiency
• All that in a limited photon budget [ < 107 total detected photons usually]
Averaging over many emitters is highly misleading 1. Average over a diffraction limit is useless - very far from peak numbers2. Average is biased – fluorescence signals select on unquenched emitters3. Product of averages and average of product is very different
36
Actual calculation – Au sphere in a pump focus
ACS Photonics 4, 710–722, (2017) 37
Record reported antenna
Hoang, Akselrod & Mikkelsen
Ag nanopatch on template-stripped Au, CdSe/CdS quantum dots- Lifetime suggests Fp > 540 – quantum efficiency presumed 20%- 1900x overal brightness increase in cw excitation
Factorized as 225 [pump ] x 2 [ Q.E. ] x 4 [collection]