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Surface-waves generated Surface-waves generated by nanoslitsby nanoslits
Philippe Lalanne
Jean Paul Hugonin
Jean Claude Rodier
INSTITUT d'OPTIQUE, Palaiseau - France
Acknowledgements : Lionel Aigouy , 40 100 Béziers
Basic diffraction problemBasic diffraction problem
Basic diffraction problemBasic diffraction problem
Motivation : providing a Motivation : providing a microscopic description microscopic description
of the interaction of the interaction between nanoslits between nanoslits
= 750 nm
320-nm-thick Ag film
Ebbesen et al., Nature 391, 667 (1998)
=/3
Motivation : ETMotivation : ET
Motivation : beaming Motivation : beaming effecteffect
H. Lezec et al., Science 297, 820 (2002)
Garcia-Vidal et al., APL 83, 4500 (2003)
Gay et al., Appl. Phys. B 81, 871-874 (2005)
20 µm
calculation
measurements
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP?
Try to answer basic questionsTry to answer basic questions
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP? – other waves?
Try to answer basic questionsTry to answer basic questions
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP? – other waves?
Influence of the geometrical parameter
Try to answer basic questionsTry to answer basic questions
slitwidth
w
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP? – other waves?
Influence of the geometrical parameter
Influence of the metal dielectric property
Try to answer basic questionsTry to answer basic questions
visible or IR illumination
silveror
gold
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP? – other waves?
Influence of the geometrical parameter
Influence of the metal dielectric property
Experimental validation
Try to answer basic questionsTry to answer basic questions
slit groove experiment
d
Young’s experiment
d
SPP generationSPP generation
n2
n1
+(x) -(x)
r0
SPP generationSPP generation
n2
n1
n2
n1
+(x) -(x)
t0
SPP generationSPP generation
S = + [t0 exp(2ik0neffh)] / [1-r0 exp(2ik0neffh)]
Easy generalizationEasy generalization
S S
(a) (b)
General theoretical formalismGeneral theoretical formalism
1) Calculate the transverse (Ez,Hy) near-field
2) make use of the completeness theorem for the normal modes of waveguides
Hy=
Ez=
3) Use orthogonality of normal modes
(z)(x)Ha(z)H(x)α(x)α (rad)σσ σSP
(z)(x)Ea(z)E(x)α(x)α (rad)σσ σSP
(x)α(x)α2(z)Ez)(x,Hdz SPy
(x)α(x)α2(z)Hz)(x,Edz SPz
P. Lalanne, J.P. Hugonin and J.C. Rodier, PRL 95, 263902 (2005)
Analytical modelAnalytical model
-The SP excitation probability ||2 scales as ||-1/2
-Immersing the sample in a dielectric enhances the SP excitation ( n2/n1)
n2
n1
+(x) -(x)
1) assumption : the near-field distribution in the immediate vicinity of the slit is weakly dependent on the dielectric properties
2) Calculate this field for the PC case
3) Use orthogonality of normal modes
012
1
1/2
221
2
Iw'nn1
Iw
nεε
nn
π4αα
describe material properties
P. Lalanne, J.P. Hugonin and J.C. Rodier, JOSAA 23, 1608 (2006)
n2
n1
+(x) -(x)
1) assumption : the near-field distribution in the immediate vicinity of the slit is weakly dependent on the dielectric properties
2) Calculate this field for the PC case
3) Use orthogonality of normal modes
012
1
1/2
221
2
Iw'nn1
Iw
nεε
nn
π4αα
describe material propertiesdescribe geometrical properties-A universal dependence of the SPP excitation that peaks at a value w=0.23.
-For w=0.23 and for visible frequency, ||2 can reach 0.5, which means that of the power coupled out of the slit half goes into heat
Analytical modelAnalytical model
tota
l SP
exc
itat
ion
pro
bab
ility
Results obtained for gold
Tot
al S
P e
xcit
atio
n e
ffic
ien
cy
model : solid curves
vectorial theory : marks
SPP? - other waves?
z
H(x,x’,z=0)
x’=0
Green function (1D)Green function (1D)
x
,kHkzH1
zxH1
x20
20
H = HSP + Hc
)xikexp(k
kSP
dm
md20
2SP
HSP =
Hc = Integral over a single real variable
zGreen function (1D)Green function (1D)
10-1
10-2
100
10-3
101 102100 101 102100
=0.633 µm =1 µm
=9 µm=3 µm
x/ x/
|H| (
a.u.
)|H
| (a.
u.)
|H| (
a.u.
)|H
| (a.
u.)
x/ x/
10-1
10-2
100
10-3
(result for silver)
HSP
Hc
(x/)-1/2
P. Lalanne and J.P. Hugonin, Nature Phys. 2, 556 (2006)
w=100 nm
-0.5
0
0.5w=352 nm
-1
0
1
=0.
852
µm
=3
µm
plane waveillumination
()
x/
x/P. Lalanne and J.P. Hugonin, Nature Phys. 2, 556 (2006)
dS
= 852 nm
S0
= 852 nm
d/
|S/S
0|2
m
m
m
m
m
PC
….. SPP only computational results
(d/
P. Lalanne and J.P. Hugonin, Nature Phys. 2, 556 (2006)
OutlineOutline
Nature of the surface wavesNature of the surface waves SPP? – other waves?
Influence of the geometrical parameter
Influence of the metal dielectric property
Experimental validation
Try to answer basic questionsTry to answer basic questions
slit groove experiment
d
Young’s experiment
d
Validation : Young’s slit experiment
H.F. Schouten et al., PRL. 94, 053901 (2005).
d
gold
glass
TM incident light
d=4.9 µm
d=9.9 µm
d=14.8 µm
d=19.8 µm
P. Lalanne, J.P. Hugonin and J.C. Rodier, PRL 95, 263902 (2005)
S = |t0 + - + exp[ikSPd)]|2 S
+ -
d
gold
*** semi-analytical modelo o o Schouten’s experiment numerical results
d=4.9µm
d=9.9µm
S
S
Validation : Young’s slit experiment
d
|S|2
|S0|2
|S/S
0|2
d (µm)
Slit-Groove experiment
G. Gay et al. Nature Phys. 2, 262 (2006) promote an other model than SPP
d Fall off for d < 5
frequency = 1.05 k0
kSP=k0 [1-1/(2Ag)] 1.01k0
silver
=852 nm
|S/S
0|2
d (µm)
dS
= 852 nm
S0
= 852 nm
computational resultso o o experiment….. SPP theory
SPP theory and computational results are in perfect agreementSPP theory and computational results are in perfect agreement
P. Lalanne and J.P. Hugonin, Nature Phys. 2, 556 (2006)
Lionel Aigouy, Laboratoire ‘Spectroscopieen Lumière Polarisée’ ESPCI, Paris
2 µm
2 µm
Gwénaelle Julié,Véronique MathetInstitut d’ElectroniqueFondamentale, Orsay, France
Near field validation
gold
TM incident light
slit slit
Real part Imaginary part
Real part Imaginary part
distance distance
----- extracted from fit computational results
total field
creeping wave ONLY
Field at a single aperture
Conclusion
•The surface wave is a combination of SPP [exp(ikSPx)] and a creeping wave with a free space character [exp(ik0x)]/x1/2 •SPP is predominant at optical frequency for noble metal•The creeping wave is dominant for >1.5 µm and for noble metals•The SPP generation probability can be surprisingly high for subwavelength slits (50%) at optical wavelengths•The probability scales as ||-1/2
•The probability is enhanced when immersing the sample•Experimental validation is difficult but on a good track