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  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. 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. Introduction

  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. Tn E S1 T1 G One photon absorption Sn kisc G kSG kTG  = absorption cross section

  7. Sn Tn E S1 kisc T1 G kSG kTG G 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

  11. Sn S E T S1 kisc G kSG kTG G Reverse Saturable Absorption (RSA) • The excited state cross section is larger than the ground state cross section. • S/G > 1 (or) T/G > 1 Tn T1 • Materials showing RSA become more opaque upon exposure to light of suitable wavelength.

  12. Output fluence Linear transmittance Sn Tn S E T S1 kisc Input fluence threshold T1 G kSG kTG G Criteria for Optical Limiting • Sequential TPA, ES > G. • ES > the pulse duration. • Wide range of incident intensities. • Low threshold. • Large non linear absorption over a broad spectral bandwidth. • ES / G ratio. • Saturation fluence.

  13. Stilbene derivatives indanthrone dye calix[n]arene tetraphenyldiamines thienyleneethynylene Reverse Saturable Absorber Chromophores Organic Molecules

  14. Porphyrins Phthalocyanines Metal Clusters Fullerenes Carbon Nanotubes Reverse Saturable Absorber Chromophores

  15. Photodetector Nd:YAG laser sample -Z +Z Techniques used • Z-scan Technique

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

  17. Porphyrins and Phthalocyanines

  18. 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

  19. Sn Tn S E T S1 kisc T1 G kSG kTG G Porphyrins: Early studies Tetraphenyl porphyrins 80ps pulse delay Fast ISC due to heavy atom effect Blau, W.; Byrne, H.; Dennis, W. M.; Kelly, J. M. Opt. Commun. 1985, 56, 25

  20. X = 2H Effect of metal centre and meso substituent Nd:YAG 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

  21. 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

  22. n=1 n=2 n =10-15 n =2 n = 1 n=10-15 Effect of conjugation % transmittance: 60%, 40% and 35% Greater the conjugation, the better is the optical limiting performance. λexc = 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

  23. (t-Bu)4PcInCl (t-Bu)4PcIn(p-CF3C6H4) Effect of - and axial- substituents Indium Phthalocyanines λexc = 532nm pulse delay: 5ns Bulky groups enhances optical limiting performances. Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001,3759

  24. 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

  25. Effect of Axial Substitution Titanium Phthalocyanines λexc = 532nm pulse delay: 5ns EWG on axial position improve the optical limiting performances. Dini, D.; Barthel, M.; Hanack, M. Eur. J. Org. Chem. 2001,3759

  26. R = n-C6H13 R = n-C10H21 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.; O’Flaherty, S. M. J. Mater. Chem. 2003, 13, 1042

  27. Heavy central atom: better optical limiting response 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

  28. λexc 570nm 605nm 695nm Polypyridyl Porphyrins Pulse delay = 1ns Duncan, T. V.; Rubtsov, I. V.; Uyeda, H. T.; Therien, M. T. J. Am. Chem. Soc.2004,126, 9474

  29. Fullerenes

  30. 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.

  31. Tn E T S1 kisc T1 G kSG kTG G Triplet-triplet absorption Range of interest: 600nm-near IR

  32. 0.21 0.05 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.

  33. C60 in PMMA C60 in toluene 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.

  34. 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

  35. Similar optical limiting efficiencies of C60 and its derivatives. Sun, Y.-P.; Riggs, J. E. Chem. Mater.1997, 9, 1268

  36. 4 1 2 3 2 1 3 4 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.

  37. 1 2 1 C60 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.

  38. Sn Tn S E T S1 kisc T1 G kSG kTG G Optical limiting mechanism • Is Reverse Saturable Absorption the only mechanism? • Optical limiting performances in solid matrix different from that in solution?

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

  40. Bimolecular processes Self quenching Annihilation Excimer-like state Riggs, J. E.; Sun, Y.-P., J. Phys. Chem. A. 1999, 103, 485.

  41. Sn Tn S1 Sex T1 Tex k k SexG TexG G Modified reverse saturable absorption model Riggs, J. E.; Sun, Y.-P., J. Phys. Chem. A. 1999, 103, 485.

  42. Carbon Onions Excimer laser: 308nm, 20ns UV-400 nitrogen laser: 337nm, 8ns Nd:YAG laser: 532 and 1064nm, 12ns Georgakilas, V.; Guldi, D. M.; Signorini, R.; Bozio, R.; Prato, M. J. Am. Chem. Soc. 2003, 125, 14268-14269

  43. 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.

  44. 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