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Plasmonics: a few basics
Philippe Lalanne Institut d'Optique d’Aquitaine, Bordeaux – France
Laboratoire Photonique, Numérique et Nanosciences (LP2N)
Photons and nanosystems
Complex nanostructures
Cold atoms, matter waves
Biophotonic
Optics & numerics (virtual reality)
outline
Field localization (10mn)
Delocalized surface plasmons on metal surfaces
Wood anomaly
Localized plasmon
The « end » of the plasmon
optics physics chemistry
The magic confinement
photonic
plasmonic
J. Takahara et al., Proc. SPIE 5604, 158 (2004). D.K. Gramotnev and Sergey I. Bozhevolnyi, plasmonics beyond the diffraction limit, Nat. Photon. 4, 83-91 (2010).
DOS
Singularity (LDOS ng)
a/l
p/a Re(kz)
gap
0
a/l
LDOS singularity in periodic systems
Experimental recronstruction of the DOS in a photonic crystal waveguide
S. R. Huisman and al., Phys. Rev. B 86, 155154 (2012)
No singularity for real waveguide
Quenching
R. Amos and W.L. Barnes, Phys. Rev. B 55, 7249 (1997).
D
Quenching is predicted by
classical electromagnetic
theory quenching is
simply described by the
dielectric constant of the
substrate material.
x+fx/t = -(e/m) E0exp(-iwt)
Dipole momentum
p(w) = -ex(w) = e0a(w)E(w)
Dielectric constant:
.. .
0.6 1 1.4 1.8 -160
-120
-80
-40
0
40
l (µm)
Re(er)
Im(er)
electron
E
t = g-1
lp = 2pc/wp
wt-we
-=wa=eim
NeN
20
2 111r
The electron sea
tm
td
w
Dielectric thickness td (nm) G
roup Index
LDOS of MIM waveguides
Ag
AsGa
w =40 nm
w =100 nm
w =350 nm
w =
singularity
dm
d
tefft
nd
l
e
e
p
-
1
Stotal=0 M
M I
Stotal>0 M
M I
kSP
Dielectric thickness td (nm)
LDOS of MIM waveguides
Dam
pin
g (
µm
-1)
dm
md
t t
Im
d
142
e
ee a
tm
td
w
w =40 nm
w =100 nm
w =350 nm
w =
Ag
AsGa
outline
Field localization
Delocalized surface plasmons on metal
surfaces
Wood anomaly
Localized plasmon
The « end » of the plasmon
Dark-field nanoscope: G.A. Zheng et al, PNAS
107, 9043-48 (2010) .
Submicron dichroic splitter: J. Liu et al, Nat.
Comm., Nov. 2011.
Plasmonic nanofocussing for near-field
spectroscopy: S. Berweger et al., Phys. Chem.
Lett. 3, 945 (2012) .
J. Pendry et al., Science 305, 847 (2004).
R. Ulrich and M. Tacke, APL 22, 251 (1973).
"SPOOF" SPP
k//
w
Génération de plasmons avec des nanostructures
Questions:
Comment peut-on mesurer ou calculer l’efficacité de génération des
plasmons?
Comment exciter efficacement les plasmons de surface?
Comment cette efficacité varie avec les principaux paramètres?
Kuzmin et al., Opt. Lett. 32, 445 (2007). S. Ravets et al., JOSA B 26, B28 (2009).
glass
Au
q
Young slit experiment
(with a single slit illuminated)
0 -40 -30 -20 -10 0 10 20 30
glass
Au
q
q TE
Kuzmin et al., Opt. Lett. 32, 445 (2007). S. Ravets et al., JOSA B 26, B28 (2009).
How to calculate the amount of SPP
generated on the surfaces?
How to calculate the amount of SPP
generated on the surfaces?
a+ a-
)(xα)(xα2dz(z)Ez),(xH 00SP0y
-
-=
)(xα)(xα2dz(z)Hz),(xE 00SP0z
-
--=
x0
z
« Overlap integral »
Orthogonality is not
implemented with
EH* products but
with EH products
PL, J.P. Hugonin and J.C. Rodier, PRL 95, 263902 (2005)
a+ a-
x
exp[-Im(kspx)]
test
x0/l
l = 940 nm and silver
z
x
x0 x0
Il est bon de disposer de formule approcher pour mieux comprendre; ces
formules ont été établie surtout pour les fentes.
Les résultats sont probablement généraux.
a b
Normalization:
-incident field E=1 effective SPP cross section
-intensity incident on the slit = 1 efficiency
SPP generation by slits
describe geometrical properties -the SPP excitation peaks at a value wl/4
-for visible frequency, |a|2 reach 0.5, which means that of the power coupled out of the
slit half goes into heat
describe material properties -Immersing the sample in a dielectric enhances the SP excitation ( n2/n1)
-The SPP excitation efficiency |a|2 scales as |em(l)|-1/2
Analytical model
2/1
1
222 -el=b=a m
n
nwf
n2
n1 me
Expliquer avec Huygens pourquoi et dire que ce
resultat devrait être vrai pour bcp de géométries
Expliquer pourquoi avec l’intégrale de
recouvrement et avec les mains
PL, J.P. Hugonin and J.C. Rodier, PRL 95, 263902 (2005) & JOSAA 23, 1608 (2006).
tota
l S
P e
xci
tati
on
pro
bab
ilit
y
solid curves
(analytical model)
marks
(overlap integral)
|a|2 |b|2
Au Au
Drude model : |e| l2
exp(-z/d1)
d1=l e1/2/2p >> l
exp(-z/d2)
d2=l e-1/2/2p cte
Surface plasmon polariton
w/c
wp/c2
w/c=k/ed
Re(kSP)
)(xα)(xα2dz(z)Ez),(xH 00SP0y
-
-=
)(xα)(xα2dz(z)Hz),(xE 00SP0z
-
--=
100
101
10-1
100
(results obtained for gold)
l (µm)
|HS
P|
H. Liu et al., IEEE JSTQE 14, 1522 (2009)
Valid for all subwavelength
indentations
2/1-em
w/l
w
effic
ien
cy
(results obtained for gold)
S. B. Raghunathan et al., Opt. Express 20, 15326-15335 (2012).
Anti-symetric illumination
(never mind!)
55%
Unidirectional SPP launching with
grooves arrays
Bull eye : H. Lezec et al., Science 297, 802-804 (2002).
2 mm
2 µm
8 μm
Launcher Left
decoupler
Right
decoupler
A. Baron et al., Nano Lett. 11, 4207 (2011).
Gaussian beam (λ = 800 nm waist = 6λ)
λ
•Launching efficiency: c+ = 60%
•Contrast > 50
R(θ)
+30° -30°
-90° +90°
•Decoupling efficiency: d = 75%
•Radiation cone: < 10°
Unidirectional SPP launcher
outline
Field localization
Delocalized surface plasmons on metal surfaces
(30mn)
Wood anomaly
Localized plasmon
The « end » of the plasmon
S. Collin et al., PRL 104, 027401 (2010).
•Historique de l’anomalie de Wood
•La description plasmonique de l’anomalie
•deux types d’onde sont mises en jeux: les plasmons et les ondes
quasi-cylindriques
•Quelle est l’influence de la longueur d’onde sur le rôle de chacune
des ondes?
•Commentaire sur le spoof plasmon
“I was astounded to find that under certain conditions, the drop
from maximum illumination to minimum, a drop certainly of
from 10 to 1, occurred within a range of wavelengths not
greater than the distance between the sodium lines”.
Rapid survey of Wood’s anomalies
Discovery of the anomaly
R. W. Wood, Philos. Mag. 4, 396 (1902).
First explanation attempt by Lord Rayleigh
Rayleigh, Proc. Royal Society (London) 79, 399 (1907)
The forced resonance explanation of Fano
U. Fano, JOSA 31, 213 (1941).
k//+mK = k0
“I was astounded to find that under certain conditions, the drop
from maximum illumination to minimum, a drop certainly of
from 10 to 1, occurred within a range of wavelengths not
greater than the distance between the sodium lines”.
Rapid survey of Wood’s anomalies
Discovery of the anomaly
R. W. Wood, Philos. Mag. 4, 396 (1902).
First explanation attempt by Lord Rayleigh
Rayleigh, Proc. Royal Society (London) 79, 399 (1907)
The forced resonance explanation of Fano
U. Fano, JOSA 31, 213 (1941).
k//+mK = kSPP (>k0)
“I was astounded to find that under certain conditions, the drop
from maximum illumination to minimum, a drop certainly of
from 10 to 1, occurred within a range of wavelengths not
greater than the distance between the sodium lines”.
Rapid survey of Wood’s anomalies
Discovery of the anomaly
R. W. Wood, Philos. Mag. 4, 396 (1902).
First explanation attempt by Lord Rayleigh
Rayleigh, Proc. Royal Society (London) 79, 399 (1907)
The forced resonance explanation of Fano
U. Fano, JOSA 31, 213 (1941).
Modern theory of grating diffraction
Fully-vectorial numerical tools: Integral, differential methods, RCWA, …
Advanced conceptual tool: « polology » 2
0P
ZTTw-w
w-w= ~
~
w
T
The extraordinary optical transmission
T. W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio and P.A. Wolff, Nature 391, 667 (1998).
l (nm)
ratio
tran
smis
sion
e- e- e-
e-
e-
e- e- e-
e-
e-
SPP-assisted transmission?
T. W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio and P.A. Wolff, Nature 391, 667 (1998).
Debated hypothesis: The electronic character of SPP helps the coupling of the energy from the surface to the holes?
Main results from mode theory
Phenomenological polology E. Popov et al., PRB 62, 16100 (2000).
Resonance-assisted tunneling L. Martín-Moreno et al., PRL 86, 1114 (2001).
Spoof plasmon J. Pendry et al., Science 305, 847 (2004).
The Fano-type formula is very elegant as it well reproduce the
spectral lineshape with o,nly 5 real parameters. It additionnally
shows that the EOT is a resonance phenomenon.
All these analysis relies on physical ‘GLOBAL’ quantities attached to periodic ensembles; they give a good
insight into the macroscopic mechanisms responsible for the transmission, but nothing is known about the
individual plasmons that are launched inbetween the holes of the array.
2
0P
ZTTw-w
w-w= ~
~
w
T
"SPOOF" SPP
k//
resonance
resonance
More insight has been provided by Martin-Moreno who showed
that the resonance occurs at interfaces and that they boosts an
evanescent tuneling.
w Pendry et al. showed that the same resonant-assisted mechanism
occurs at low frequencies, and introduced the concept of spoof
plasmons.
SPP-assisted transmission?
If one derives a model of the EOT where only SPP are assumed to
carry the energy between adjacent hole chains and compares with
fully-vectorial computations, then one should allow us to quantify
what is really due to SPP in the EOT.
Microscopic SPP model
r t
a
b
t
b
in-plane reflection-transmission of SPP
coupling of SPP to free-space
tr-
ab
l
l
l
l=
aik
pT
SPexp2
20
2
201 1
H. Liu and P. Lalanne, Nature (London) 452, 448 (2008).
(for periodic arrays)
Actual SPP role in the EOT
H. Liu and PL, Nature (London) 452, 448 (2008).
Experimental evidence: F. van Beijnum et al., Nature 492, 411 (Dec. 2012).
0.95 1 1.05 1.1 1.15
0
0.1
0.2
a=0.68 µm
Tra
nsm
itta
nce
l/a
Normal incidence
RCWA SPP model
q2
Tra
nsm
issio
n
wavelength (nm)
750 800 850 900
0
0.05
0.1
spectra32thefromfitted
arecomplexreal
ik1T
321
SP
2
2
20
2
2012
...,q
p&p,p
a
ppq
=
tr=
tr--l
l
l
l=
exp
Normal
incidence
Measurement performed in Martin van Exter’s group (Leiden)
q=2
2a
1a
3a
q=3
1a
q = 1
q = 4
q = 2
q = 6
Direct experimental proof
q2
Tra
nsm
issio
n
wavelength (nm)
750 800 850 900
0
0.05
0.1
F. van Beijnum et al., Nature 492, 411 (Dec. 2012)
tr-
ab
l
l
l
l=
aexp
p
qikTq
SP2
20
2
2012 1
q = 1
q = 4
q = 2
q = 6
The 5 coefficients p1 (real), ab and r+t
(complex) are fitted for q = 2,3 …7
Direct experimental proof
total field
SPP field only
Quasi-CW field only
P. Lalanne, J.P. Hugonin, H.T. Liu and B. Wang, Surf. Sci. Rep. 64, 453 (2009)
l = 940 nm and silver
Quasi-cylindrical wave
Highly accurate for x < 10l
F(x) = exp(ik0x) (x/l)-m
m varies from 0.9 in the
visible to 0.5 in the far IR
102 100
10-2
100
10-4
10-6
|F(x
)| (
a.u
.)
x/l
1/x3
1/x
silver @ l=1 µm
Quasi-cylindrical wave
10-1
10-2
100
10-3
101 102 100 101 102 100
l=0.6 µm l=1 µm
l=9 µm l=3 µm
x/l x/l
|H| (a
.u.)
|H
| (a
.u.)
|H| (a
.u.)
|H
| (a
.u.)
x/l x/l
10-1
10-2
100
10-3
HSP
HCW
(x/l)-1/2
PL and J.P. Hugonin, Nature Phys. 2, 556 (2006). PL et al., Surf. Sc. Report (2009).
(result for silver)
HSP 1/|em|1/2
HCW cte
Frequency dependence (important)
2/32 d
m
pe
e
(perfect metal)
q (°)
l=0.6 µm
l=1 µm
l=3 µm
l=10 µm
PC
S. Ravets et al., JOSA B 26, B28 (2009).
Fa
r-fi
eld
in
ten
sit
y (
a.u
.)
SPP mainly
Quasi-CW only
Quasi-CW & SPP
Quasi-CW mainly
J. Pendry et al., Science 305, 847 (2004).
"SPOOF" SPP
k//
w
Spoof=coherent interaction of holes
with quasi-cylindrical waves
Field localization
Delocalized surface plasmons on metal surfaces
Wood anomaly (60 mn)
Localized plasmon
The « end » of the plasmon
outline
Metallic resonance
nanoantenna
sensing
Solar cell
Frequency conversion
How efficiently can you excite it?
-from the near field? Purcell?
-from far field?
What is the resonance mode?
-how to define it « properly »?
-What is the mode volume?
-What are the limiting quantities for Q?
Application to sensing
-analytical formula of the resonance shift
Metallic resonance
+ +
+
+ +
- -
-
- -
E
bh
bhVee
e-e=a
23
J.D. Jackson, Classical Electrodynamics
plane wave E0
he
be
V << l3
02 =ee bh
Resonance is achieved for a
single fixed wavelength, such
that 02 =ee bh
Why tiny metallic NP resonate?
52
Cross-section shrinks to zero, neff of the plamonic mode diverges, and L shrings!
(The Fabry-Perot electric-dipole resonance mode scales down (no cutoff) )
IMIM MIM IMI
L
td
m
d
d
efft
npe
el-= 0
d
d
m
eff
tRe
nReL
e
ep-=
l-
2
20 /
J. Yang et al., Opt. Express 20, 16880-16891 (2012)
"Ultrasmall metal-insulator-metal nanoresonators: impact of slow-wave effects on the quality factor"
Resonance is achieved for any
wavelength, just by scaling
down dimensions.
Why tiny metallic NP resonate?
Q factor at deep sub-λ scale
Quasi-static limit : Q factor of a localized plasmon resonance is
determined only by εmetal.
εω
ωQε
metal0S
metal
Re( )
=2Im( )
F. Wang et al., Phys. Rev. Lett. 97, 206806 (2006).
J. Yang et al., Opt. Express 20, 16880-16891 (2012)
"Ultrasmall metal-insulator-metal nanoresonators: impact of slow-wave effects on the quality factor"
(Ag: Q ~ 70 @ λ=600nm)
Far-field excitation
Near-field
excitation
Excitation of metal resonance
mmmm
mmm
i
i
ErH
HE
HE
~)~,(~~
~~~
ω~2Imω~ReQω~frequencycomplexaforsourcewithout
equationssMaxwell'ofsolutionsare~
,~
modesnormalquasiThe
m
mm
wew-=
mw=
=
-
0
What is a metallic resonance?
w rrkk as~
expcomplex~
complex~ i
wwew-w
w-=wa rErErrr minc
mm
~,,d~, 3
Excitation coefficient a
1dif 3 =ww-ww rHμHEεE~~~~
Energy of a dispersive
material? yes but only when
absorption is small. No
energy consideration in the
derivation.
Very easy!
Only a single hypothesis : material is reciprocal
rErErE m
m
minc
~,, waw=w
Far-field excitation
Near-field
excitation The scattered fiedl is expanded in
the QNM basis
Complex coordinate
transform (PML)
X = a(1+im) x
Y = a (1+im) y
Z = a (1+im) z
Analytical
continuation in the
complex plane with
PMLs
Rkrk im1iexpiexp ~~
remove the divergence problem for
suitable m’s by transforming the
exponentially diverging field into an
exponentially damped field
0
The normalization issue
Complex coordinate
transform (PML)
X = a(1+im) x
Y = a (1+im) y
Z = a (1+im) z
is an invariant under
space coordinate transforms
is invariant too and can be calculated with
any PML, by computing the integral in real
space and in the PML.
w rEεE 3d
rEεE 3dV ww=~~
m
First (?) time the field in the PML is explicitly considered to evaluate a physical quantity.
The normalization issue
Open-source software for resonance
calculation
0
4
8
12
50 nm
1w~
2w~3w~
Re(w)
Im(w)
4w~
2w~ 3w~ 4w~1w~
Freeware implemented with COMSOL multiphysics can be downloaded at
www.lp2n.institutoptique.fr
Q. Bai,et al., Opt. Express 21, 27371 (2013).
Coll. Mathias Perrin/LOMA
0.7 0.8 0.9 1 1.1 1.2 0
0.02
0.04
0.06
0.08
Wavelength (µm)
0.7 0.8 0.9 1 1.1 1.2 0
100
200
300
400
Wavelength (µm)
Purcell factor Extinction cross section (µm2)
wwew-w
w-=wa rErErrr minc
3
m
~,,d~,
Q. Bai,et al., Opt. Express 21, 27371 (2013).
Cro
ss S
ecti
on
700 750 800 850 900 950 0
1
2
3
4
5
Wavelength (nm)
rrErEr 3d
perturb
~~~,~~
.
wew-=w
w~Re
wd ~Imd
Application to sensing
J. Yang et al., (in preparation)
w~Re w~Im
A. Curto et al., Science 329, 930 (2010).
The quantum-dot luminescence is totally governed by the antenna
- radiation diagram
- Purcell factor
Yagi-Uda antenna
Nano-antenna
Nano-antenna
G.M. Akselrod et al., Nat. Photon. DOI:
10.1038/NPHOTON.2014.228
“Probing the mechanisms of large Purcell enhancement in
plasmonic nanoantennas”
Purcell
Radiation
efficiency
20
220
20
2
20
0 )(4 w-ww
w
w
w=
Q
with4
3
M
3
2 V
Q
n
l
p=
Classical Lorentzian shape
F
F
Classical Purcell formula
e
e=
2
32
M
)()(max
d)()(V
rEr
rrEr
~
~Only valid for large Q
(error scales as 1/Q as
Q)
w-wd=n
nDOS ~
w
DO
S
modal-expansion of the LDOS
R.K. Chang and A.J. Campillo, Optical processes in microcavities, (World Scientific, 1996).
w-wd=n
nDOS ~
2
n
n
nLDOS rErr~~, ew-wd=w
w
DO
S
R.K. Chang and A.J. Campillo, Optical processes in microcavities, (World Scientific, 1996).
1dV
32
nnn =e= rrErEE~~
,~
modal-expansion of the LDOS
w-wd=n
nDOS ~
2
n
n2n
2n
n 1LDOS rErr
~
~, e
gw-wp
g=w
w
DO
S
R.K. Chang and A.J. Campillo, Optical processes in microcavities, (World Scientific, 1996).
2
n
n
nLDOS rErr~~, ew-wd=w
1dV
32
nnn =e= rrErEE~~
,~
modal-expansion of the LDOS
with4
3
M
3
2
l
p=
V
QRe
nF
Revisiting the Purcell formula
20
20
3
M
)r(2
dV
uE
rEεE
e
ww=
~
n
~~
w
w-w
w-ww
w
w
w=
M
M
0
0
20
220
20
2
20
0 Re
Im21
)(4 V
VQ
QF
Derivation based on reciprocity arguments, see C. Sauvan et al., PRL 110, 237401 (2013) & Q.
Bai et al., Opt. Express 21, 27371 (2013).
Circle: Green-tensor calculation (decay in all modes)
Blue line: revised Purcell formula (with a single mode)
Non-Lorentzian response with
metallic resonance
00010
i73V3
1,
l--=
00010i34V
3
2,
l=
the contribution of a quasi-normal mode to the total
power radiated by a source may be detrimental (it may
reduce the decay rate), even when the frequencies of the
source and the mode are matched.
Multi-resonance case
85 nm
145 nm
45 nm
Au
80 nm
20 nm
outline
Field localization
Delocalized surface plasmons on metal surfaces
Wood anomaly
Localized plasmon (1H20)
The « end » of the plasmon
0 2 4 6 8
Heat diffusion –
acoustic relaxation
e- - phonon
relaxation
e- abs
delay (ps)
ΔR
/R (
10
3 )
t e-e
= 1
00
fs
te-ph = 1 ps
0
0.5
1.5
1
pump
probe
S.D. Brorson, J.G. Fujimoto and E.P. Ippen, PRL 59 (1987).
The plasmon decay and then what?
SPP7 2015: first apparition of hot
electrons in the main topic list of the
SPP conference series
First review paper appeared in Jan. 2015
Hot electrons=hot topic
Many applications
Plasmon induced hot carriers
M.W. Knight et al., Science 332,702 (2011).
-photodetectors with spectral responses
circumventing band gap limitations
-chemical catalysis close to metal surfaces
Même quand il meurt, le plasmon renait de ses cendres.
Le plasmon est éternel, « offrer donc un plasmon »
The end
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