Nonlinear Optical Response of Nanocavities in Thin Metal Films Yehiam Prior Department of Chemical...
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Nonlinear Optical Response of Nanocavities in Thin Metal Films Yehiam Prior Department of Chemical Physics Weizmann Institute of Science With Adi Salomon - Weizmann Institute, Rehovot Joseph Zyss, Marcin Zielinsky - ENS Cachan, France Maxim Sukharev - Arizona State University, Arizona Tamar Seideman - Northwestern University, Illinois Israel Chemical Society Annual Meeting February 2012
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Transcript of Nonlinear Optical Response of Nanocavities in Thin Metal Films Yehiam Prior Department of Chemical...
Nonlinear Optical Response of Nanocavities in Thin Metal Films
Yehiam PriorDepartment of Chemical Physics
Weizmann Institute of Science
With
Adi Salomon - Weizmann Institute, Rehovot
Joseph Zyss, Marcin Zielinsky - ENS Cachan, France
Maxim Sukharev - Arizona State University, Arizona
Tamar Seideman - Northwestern University, Illinois
Robert Gordon - University of Illinois, Illinois
Israel Chemical Society Annual Meeting February 2012
Nano Particles
Notre Dame, ParisQuantum size effect
Gold nanoparticles
Semiconductor nanoparticles
Nano “structures”
• Transmission with d<<λ
• When arrays are used – sharp interference peaks are observed
• The transmitted intensity is much larger than classical [~(d/λ)4]
• Explained in terms of Plasmonic excitations in the metal
Nano Holes
The periodicity determines the color
Transmission through an array of nano holes
pSEM
We understand the linear optical properties of these structures fairly well.
What about their NONLINEAR optical properties?
OUTLINE
• SHG from Individual cavities
• From isolated to coupled cavities
• Plasmon-molecule interactions
• Conclusions and future directions
OUTLINE
• SHG from Individual cavities
• From isolated to coupled cavities
• Plasmon-molecule interactions
• Conclusions and future directions
Focused Ion Beam (FIB) fabricated shapes
What is the SHG response of a nano-hole ?
Ag film ~ 200nm, evaporated on glass
20 40 60 80 100
10
20
30
40
50
60
70
80
90
100
0
100
200
300
400
500
600
700
800
900
1000
SHG from non interacting triangles
ω 2ω
Experimental set-up
150nm
SHG from Individual triangles with different side length
170nm 190nm
220nm 245nm 285nm
SHG from Individual triangles with different side length
150 200 250 300 350
5000
10000
15000
20000
25000
30000
SH
G(i
nte
rgra
ted
sig
na
l)
side length [nm]
Experimental condition: 200nm Ag film evaporated on glass (n = 1.5)FW=940nm thus SHG at 470nm
SHG from Individual holes - size dependence
0.10 0.15 0.20 0.25 0.30 0.350
10000
20000
30000
Side Length /Fundamental Wavelength
SH
G (
inte
rgra
ted
sign
al)
0.1 0.2 0.3
200
400
600
800
1000
1200
SH
G (
Inte
grat
ed s
igna
l)
side length /Fundamental wavelength
SHG from Individual holes – wavelength dependence
400 420 440 460 480 5000
200
400
960920880840
400 420 440 460 480 5000
400
800
1200
960920880
840
a=210nm
An oversimplified model
For equilateral triangular cavities:
For square cavities: Fabry-Pérot “bouncing ball” :
“diamond-like” :
An oversimplified model
SHG Polarization properties
Photo diode/
x
PhotoDiode/
y
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180 0
Polarization properties for an individual cavity
OUTLINE
• SHG from Individual cavities
• From isolated to coupled cavities
• Plasmon-molecule interactions
• Conclusions and future directions
• What happens when the holes are closer to each other, and are allowed to interact?
• We observe a gradual transition from isolated holes to coupled ones (similar to the assembly of a crystal from individual molecules)
• The intensity, as well as the polarization properties change
From individual to coupled cavities
Individual hole Coupled holes
From individual to coupled cavities
2000
4000
6000
30
210
60
240
90
270
120
300
150
330
180 0
200
400
600
800
30
210
240
270
120
300
150
330
180 0
90
60
(a) (b) (c)
From individual to coupled cavities: Polarization
5 10 15 20 25 30 35
10
15
20
25
30
35
40
45
50 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
c
b
a
d
From individual to coupled cavities: Polarization
200
400
600
30
210
60
240
90
270
120
300
150
330
180 0
(a) (b)
(d)
5000
10000
15000
30
210
60
240
90
270
120
300
150
330
180 0
(c)
From individual to coupled cavities: Intensity
Individual (650nm) coupled (450nm)
Silver
Gold
From individual to coupled cavities: λ dependence
Smaller signal for shorter wavelengths
From individual to coupled cavities: observations
1. Individual holes give rise to SHG
2. Two types of coupling:
a. “Light only” coupling – the plasmons generated in different holes do not interact directly (i.e. the gold sample), the dependence on the number of holes is quadratic
b. Plasmon coupling - the plasmons interact directly, the dependence on the number of holes is more than quadratic
3. In both cases, the coupling is characterized by different polarization properties
4. For direct plasmonic coupling, metal must support plasmonic propagation at both the fundamental and the second harmonic frequencies
1
2 3
scaled in microns
scal
ed in
mic
rons
0 2 4 6 8 10
0
2
4
6
8
10100
200
300
400
500
600
7001
2 3
Hot Spots
1
2 3 12 3
Hot Spots
1
Hot Spots
Giant SHG signals at the hot spots (almost 1000 times bigger)
OUTLINE
• SHG from Individual cavities
• From isolated to coupled cavities
• Plasmon-molecule interactions
• Conclusions and future directions
2.0 2.2 2.4 2.6 2.8 3.00
1
Energy [eV]
Tra
nsm
issi
on [
a.u]
Absorbance [a.u.]
0.0
0.5
1.0
Plasmon-molecule interaction – the system
2.4
2.6
2.8
3 340
360
380
400
420
440
4600
0.5
1
1.5
Energy[eV] Slit arr
ay p
eriodici
ty [nm]
Tra
nsm
issi
on[a
.u.]
WaveVector[m-1]
Ene
rgy
[ev]
1.3 1.4 1.5 1.6 1.7 1.8 1.9
x 105
2.4
2.5
2.6
2.7
2.8
2.9
3
Molecular state
Upper polariton Lower polariton
Plasmon-molecule interaction – avoided crossing
WaveVector [m-1]E
nerg
y [e
V]
(a) (b)
1.4 1.5 1.6 1.7 1.8 1.9
x 105
2.4
2.62
2.8
3
o Collective mode Molecular state
Upper polariton Lower polariton
Energy [eV]
Tra
nsm
issi
on [
a.u.
]
2.3 2.4 2.5 2.6 2.7 2.8 2.9 3
Plasmon-molecule interaction – strong coupling
Ene
rgy
[eV
]
Spacer thickness[nm]
Plasmon-molecule interaction – strong coupling, with a spacer layer
OUTLINE
• SHG from Individual cavities
• From isolated to coupled cavities
• Plasmon-molecule interactions
• Conclusions and future directions
Conclusions and future directions
1. We observed coherent SHG from individual nanocavities
2. Size and shape matter - resonances are observed
3. Two types of coupling: light mediated and plasmon mediated, giving rise to a gradual transition to a “crystal”
4. Polarization properties provide excellent characterization
5. Additional experiments and theory are needed to fully and quantitatively understand the results
6. Calculations for strong coupling with molecules
7. Engineered (nonlinear) optical properties are possible
8. Hot spots are observed, with a potential for high sensitivity spectroscopy (to the single molecule level ?)
Thank you
Hot Spots
Giant SHG signals at the hot spots (almost 1000 times bigger)
scaled in microns
scal
ed in
mic
rons
0 2 4 6 8 10
0
2
4
6
8
10100
200
300
400
500
600
700
1
2 3
scaled in microns
scal
ed in
mic
rons
0 2 4 6 8 10
0
2
4
6
8
10100
200
300
400
500
600
7001
2 3
Hot Spots
2.2 2.4 2.6 2.8 3
4.5
2.2 2.4 2.6 2.8 3
3.5
10D
20D
30D40D
1e245e24
1e25
5e26
3e25
Figure 3:(a)
(b)
Energy [eV]Energy [eV]
Tra
nsm
issi
on [
a.u.
]
Tra
nsm
issi
on [
a.u.
]0.0 6.0x1012
0
100
200
Dipole moment [Debye]
RS
(meV
)
√M density [m-3]
RS
(meV
)
0 20 400
100
200
