opticallimitingmaterials光学材料限制48

Sn
Sn
S
E S1
S
E S1
Tn
T kisc
T1
G
kSG
G kSG
kTG
G
G
Three-level energy diagram
Four-level energy diagram
Reverse Saturable Absorption (RSA)
• The excited state cross section is larger than the ground state cross section.
• Sequential TPA, ES > G. • ES > the pulse duration. • Wide range of incident intensities.
• Low threshold.
• Large non linear absorption over a broad spectral bandwidth.
• Output s. input fluence
Input fluence
Transmission
• Transmission vs. input energy
Input energy
Porphyrins and Phthalocyanines
Porphyrins and Phthalocyanines
• Conclusion
Introduction
• Lasers are used in: CD players, scanners, laser pointers, spectroscopic studies, optical sensors, astronomy, military, etc.
Porphyrins
N
N
M
N
N
Phthalocyanines
N
N
N
N
M
N
N
N
N
Metal Clusters
Fullerenes
Carbon Nanotubes
Techniques used
• Z-scan Technique
Nd:YAG laser
sample
-Z
+Z
Photodetector
Output fluence
TTP (H) TTP (Zn) TTP (Pb) TTMSAP (H) TTMSAP (Zn) TTMSAP (Pb)
G
10-17 cm2
1.71 3.07 0.63 1.91 0.58 0.53
S
10-17 cm2
4.0 7.3 8.3 17 -
T
10-17 cm2
2.5 4.1 6.7 5.9 18 24
Shorter pulse duration Sn
S
E S1
G
X kisc
kSG
G Three-level energy diagram
Longer pulse duration Tn T1
Dependence on the laser pulse
Shorter pulse duration
Longer pulse duration
Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759
Indium Naphthalocyanines
Optical limiting properties: similar to InPcs Increase in solubility. Q-band red shifts to ~800nm
Porphyrins: Early studies
Sn
Tetraphenyl porphyrins
Tn
NN M
NN
NN M
NN
80ps pulse delay
S
E
S1
T kisc
G
kSG
T1
kTG
G
Molecule H2TPP CoTPP
f
9 ns <0.1ns
G (10-17 cm2) 1.6 5
Effect of - and axial- substituents
Indium Phthalocyanines
λexc = 532nm pulse delay: 5ns
(t-Bu)4PcInCl (t-Bu)4PcIn(p-CF3C6H4)
Bulky groups enhances optical limiting performances.
Qureshi, F. M.; Martin, S. J.; Long, X.; Bradley, D. D. C.; Henari, F. Z..; Blau, W. J.; Smith, E. C.; Wang, C. H.; Kar, A. K..; Anderson. H. L. Chemical Physics, 1998, 231, 87
• Beyond the threshold, the flux of photons remains constant.
Output fluence
Linear transmittance
threshold
ideal real
Input fluence
Physical processes causing optical limiting effects
• Introduction
Contents
• Optical limiters and Reverse Saturable Absorption
• Chromophores
– Porphyrins – Phthalocyanines – Fullerenes
• Optical Limiting Studies
N
N
M
N
N
Versatility, architectural flexibility, high thermal and environmental stability, inexpensiveness, non-toxicity and ease of processing.
N
N
N
N
M
N
N
N
N
Tailoring the electronic properties: -70 different metal atoms -Substitution on the ring -Axial substitution
S Absorption
Refraction
Reflection Scattering
One photon absorption
Sn
E S1
G kSG
G
kisc kTG
Tn T1
= absorption cross section
Five-level energy diagram
Sequential Two photon absorption
S/ G 3.8
T/ G
S1 Sn
3.0
T1 Tn
Fast ISC due to heavy atom effect
Blau, W.; Byrne, H.; Dennis, W. M.; Kelly, J. M. Opt. Commun. 1985, 56, 25
Effect of metal centre and meso substituent
• ES / G ratio.
Sn
Tn
S
E
S1
T kisc
G
kSG
T1
kTG
G
Linear transmittance
Output fluence
• Saturation fluence.
threshold Input fluence
Reverse Saturable Absorber Chromophores
Q- bands are red-shifted through 2H, Zn and Pb. Pb derivatives are better optical limiters.
McEwan. K. J.; Bourhill. G.; Robertson. J. M.; Anderson. H. L. Journal of Nonlinear Optical Physics & Materials, 2000, 9, 451
Sn
S E
S1
Tn
T
kisc
T1
G kSG kTG
G
Excited state which could absorb
Dependence on the laser pulse
Shorter pulse duration
Longer pulse duration
Dependence on the laser pulse
Heavy Atom Effect
1,4,8,11,15,18,22,25octaalkylphthalocyanines
R = n-C6H13 R = n-C10H21
Auger, A.; Blau, W., J.; Burnham, P. M.; Chambrier, I.; Cook, M. J.; Isare, B.; Nekelsona, F.; O’Flaherty, S. M. J. Mater. Chem. 2003, 13, 1042
• S/ G > 1
(or)
T/ G > 1
Sn
Tn
S
E
S1
T kisc
G
kSG
T1
kTG
G
• Materials showing RSA become more opaque upon exposure to light of suitable wavelength.
Criteria for Optical Limiting
• Damages skin tissues and causes blindness.
• “Smart materials” transparent under ordinary ambient light conditions, but can absorb or block intense laser light over a broad wavelength range.
Organic Molecules
O
O
NH
HN
O
O
indanthrone dye
Stilbene derivatives
calix[n]arene
tetraphenyldiamines
thienyleneethynylene
Reverse Saturable Absorber Chromophores
• Development of optical limiting materials that rely on reverse saturable absorption.
Optical Limiting Materials
• Nonlinear optical materials whose transmittance decreases significantly with increasing light fluence.
Effect of conjugation
n =10-15 n =2 n=1
n=1
n=2
λexc = 532nm pulse delay: 500ps
% transmittance: 60%, 40% and 35%
n=10-15
Greater the conjugation, the better is the optical limiting performance.
Nd:YAG laser: 532nm Pulse delay: 80ps, 14ns
X = 2H
McEwan. K. J.; Bourhill. G.; Robertson. J. M.; Anderson. H. L. Journal of Nonlinear Optical Physics & Materials, 2000. 9, 451
Titanium Phthalocyanines
λexc = 532nm pulse delay: 5ns
RIII
RIV
a
H
t-Bu
c
H
CH2CN
b
H
CHO
d
CN
CN
EWG on axial position improve the optical limiting performances.
Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759
InPcs: Optical limiter in blue region InNcs: Optical limiter in red region
Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001, 3759
Effect of Axial Substitution