Optical Limiting Materials

1
Optical Limiting Materials
Rupesh Narayana-Prabhu
2
Contents

• Introduction
• Optical limiters and Reverse Saturable Absorption
• Chromophores
• Porphyrins
• Phthalocyanines
• Fullerenes
• Optical Limiting Studies
• Conclusion

3
Introduction

• Lasers are used in CD players, scanners, laser
  pointers, spectroscopic studies, optical sensors,
  astronomy, military, etc.
• 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.
• Development of optical limiting materials that
  rely on reverse saturable absorption.

4
Optical Limiting Materials

• Nonlinear optical materials whose transmittance
  decreases significantly with increasing light
  fluence.
• Beyond the threshold, the flux of photons remains
  constant.

Linear transmittance
Output fluence
ideal
real
Input fluence
threshold
5
Physical processes causing optical limiting
effects
S
Absorption
Refraction
Reflection
Scattering
6
One photon absorption
Sn
kisc
?G
kSG
kTG
? absorption cross section
7
Five-level energy diagram
Sequential Two photon absorption
?S
?T
Excited state which could absorb
8
Dependence on the laser pulse
Shorter pulse duration
Longer pulse duration
9
Dependence on the laser pulse
Shorter pulse duration
Longer pulse duration
Sn
Tn
?S
E
S1
X
kisc
T1
?G
kSG
G
Three-level energy diagram
10
Dependence on the laser pulse
Shorter pulse duration
Longer pulse duration
Sn
Sn
Tn
?S
?S
E
E
?T
S1
S1
kisc
T1
?G
?G
kSG
kSG
kTG
G
G
Three-level energy diagram
Four-level energy diagram
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Reverse Saturable Absorption (RSA)

• The excited state cross section is larger than
  the ground state cross section.
• ?S/?G gt 1
• (or)
• ?T/?G gt 1

Tn
T1

• Materials showing RSA become more opaque upon
  exposure to light of suitable wavelength.

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Reverse Saturable Absorption vs. Two Photon
Absorption
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Criteria for Optical Limiting

• Sequential TPA, ?ES gt ?G.
• ?ES gt the pulse duration.
• Wide range of incident intensities.
• Low threshold.
• Large non linear absorption over a broad spectral
  bandwidth.
• ?ES / ?G ratio.
• Saturation fluence.

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Reverse Saturable Absorber Chromophores
Organic Molecules
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Reverse Saturable Absorber Chromophores
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Techniques used

• Z-scan Technique

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Output fluence

• Output vs. input fluence
• Transmission vs. input energy

Input fluence
Transmission
Input energy
18
Porphyrins and Phthalocyanines
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Porphyrins and Phthalocyanines

• Versatility, architectural flexibility, high
  thermal and environmental stability,
  inexpensiveness, non-toxicity and ease of
  processing.
• Tailoring the electronic properties
• 70 different metal atoms
• Substitution on the ring
• Axial substitution

20
Porphyrins Early studies
Tetraphenyl porphyrins
80ps pulse delay
Molecule ?f ?G (10-17 cm2) ?S/?G ?T/?G
H2TPP 9 ns 1.6 3.8   S1 ? Sn
CoTPP lt0.1ns 5   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
21
Effect of metal centre and meso substituent
NdYAG laser 532nm Pulse delay 80ps, 14ns
McEwan. K. J. Bourhill. G. Robertson. J. M.
Anderson. H. L. Journal of Nonlinear Optical
Physics Materials, 2000. 9, 451
22
?G 10-17 cm2 ?S 10-17 cm2 ?T 10-17 cm2
TTP (H) 1.71 4.0 2.5
TTP (Zn) 3.07 7.3 4.1
TTP (Pb) 0.63 - 6.7
TTMSAP (H) 1.91 8.3 5.9
TTMSAP (Zn) 0.58 17 18
TTMSAP (Pb) 0.53 - 24
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
23
Effect of conjugation
transmittance 60, 40 and 35
Greater the conjugation, the better is the
optical limiting performance.
?exc 532nm pulse delay 500ps
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
24
Indium Phthalocyanines
Effect of ?- and axial- substituents
?exc 532nm pulse delay 5ns
Bulky groups enhances optical limiting
performances.
Dini, D. Barthel, M. Hanack, M. Eur. J. Org.
Chem. 2001, 3759
25
Indium Naphthalocyanines
Optical limiting properties similar to
InPcs Increase in solubility. Q-band red shifts
to 800nm
InPcs Optical limiter in blue region InNcs
Optical limiter in red region
Dini, D. Barthel, M. Hanack, M. Eur. J. Org.
Chem. 2001, 3759
26
Effect of Axial Substitution
Titanium Phthalocyanines
?exc 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
27
Heavy Atom Effect
1,4,8,11,15,18,22,25- octaalkylphthalocyanines
Auger, A. Blau, W., J. Burnham, P. M.
Chambrier, I. Cook, M. J. Isare, B. Nekelsona,
F. OFlaherty, S. M. J. Mater. Chem. 2003, 13,
1042
28
Im?(3) (esu)
R n-C6H13 1 M H, H (6.6 1.3) x 10-12
6 M Zn (1.5 0.3) x 10-11
R n-C10H21 2 M H, H (5.8 1.1) x 10-12
7 M Zn (9.1 1.8) x 10-12
Heavy central atom better optical limiting
response
Auger, A. Blau, W., J. Burnham, P. M.
Chambrier, I. Cook, M. J. Isare, B. Nekelsona,
F. OFlaherty, S. M. J. Mater. Chem. 2003, 13,
1042
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Effect of ?- and axial- substituents

• The absence of any group with strong electronic
  character in Ar substituents
• small decreases of transmittance.
• high threshold intensity value.

Vagin, S. Barthel, M. Dini, D. Hanack, M.
Inorg. Chem. 2003, 42, 2683
30
Gallium Derivatives
?exc 532nm pulse delay 5ns
F atoms increases solubility. 8 is a better
optical limiter.
Yang, G. Y. Hanack, M. Lee, Y. W. Chen, Y.
Lee, M. K., Y. Dini, D. Chem. Eur. J. 2003, 9,
2758.
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Polypyridyl Porphyrins
Pulse delay 1ns
  ? (nm) (G.S.) ? (nm) (E.S.) ?T (?s) ?E/?G
RuPZn 638 884 44 75
OsPZn 640 964 0.86 163
RuPZnA 682 931 24 227
OsPZnA 704 985 1.08 135
RuPZnOs 710 1000 .079 324
Duncan, T. V. Rubtsov, I. V. Uyeda, H. T.
Therien, M. T. J. Am. Chem. Soc. 2004, 126, 9474
32
Fullerenes
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Fullerenes Early studies

• Tutt and Kost (1992) C60 in toluene solution is
  an excellent optical limiter.
• C70, C76 , C78 and C84 have also been
  investigated.
• C60 is by far the best in fullerene family.

Tutt, L. W. Kost, A. Nature, 1992, 356, 225.
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Triplet-triplet absorption
Range of interest 600nm-near IR
35
Solvent Dependence

• Solvent independent, but varies in solvents
  containing EDG.
• N,N-diethylaniline (DEA) or N,N-dimethylaniline
  (DMA) Inter-molecular electron transfer.

C60 h? ? C60 C60 DEA ? (C60-DEA) ?
C60? DEA?
Ghosh, H. N. Pal, H. Sapre, A. V. Mittal, J.
P. J. Am. Chem. Soc. 1993, 115, 11722.
36
Medium Dependence

• Weaker responses in polymethylmethacrylate (PMMA)
  or poly(propionylethyleneimine) (PPEI) or
  sol-gel glasses.
• Medium Viscosity dependent.

Kost, A. Tutt, L. Klein, M. B. Dougherty, T.
K. Elias, W. E. Opt. Lett. 1993, 18, 334.
37
Fullerene derivatives

• Derivatization increases the solubility in
  various solvents and eases polymerization.

16
15
17
Sun, Y.-P. Riggs, J. E. Chem. Mater. 1997, 9,
1268
38
Similar optical limiting efficiencies of C60 and
its derivatives.
Sun, Y.-P. Riggs, J. E. Chem. Mater. 1997, 9,
1268
39
Multiple-functionalized methano-C60
dicarboxylates
532nm 5ns
Optical limiting responses of the multiple
functionalized methano-C60 dicarboxylates are all
weaker than those of the parent C60 and the
mono-functionalized derivatives.
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C60-polystyrene polymers
The optical limiting responses of pendant
polymers are weaker than those of C60 or the
model compounds.
Sun, Y. -P. Lawson, G. E. Huang, W. Wright, A.
D. Moton, D. K. Macromolecules, 1999, 32, 3747.
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Optical limiting mechanism

• Is Reverse Saturable Absorption the only
  mechanism?
• Optical limiting performances in solid matrix
  different from that in solution?

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Factors

• Medium viscosity
• Concentration of C60
• As viscosity and concentration increases, the
  system has a weak optical limiting property.
• Bimolecular processes ?

43
Bimolecular processes
Self quenching
Annihilation
Excimer-like state
Riggs, J. E. Sun, Y.-P., J. Phys. Chem. A. 1999,
103, 485.
44
Modified reverse saturable absorption model
Riggs, J. E. Sun, Y.-P., J. Phys. Chem. A. 1999,
103, 485.
45
Phthalocyanine-fullerene derivative
CuPc-C60 is better optical limiter than CuPc or
C60 itself.
Zhu, P. Wang, P. Qiu, W. Liu, Y. Ye, C.
Fang, C. Song, Y. Appl. Phys. Lett. 2001, 78,
1319.
46
Carbon Onions
Excimer laser 308nm, 20ns UV-400 nitrogen laser
337nm, 8ns NdYAG laser 532 and 1064nm, 12ns
Georgakilas, V. Guldi, D. M. Signorini, R.
Bozio, R. Prato, M. J. Am. Chem. Soc. 2003, 125,
14268-14269
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Conclusion

• Optical limiting materials rely on the phenomenon
  of reverse saturable absorption.
• Porphyrins, phthalocyanines, naphthalocyanines
  and fullerenes are good candidates in the
  visible-near IR range.
• Become more opaque upon exposure to light of
  suitable wavelength and hence could be used to
  protect eye or optical sensors from the intense
  laser source.

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Acknowledgement

• Prof. Russell H. Schmehl
• Dr. D. Kumaresan
• Heidi Hester
• Srivathsa Vaidya
• Kalpana Shankar
• David Karam
• Monica Posse
• The Chemistry Department, Tulane University
• Friends at Tulane