7 October 1996 Nonlinear absorption of tetrabenzporphyrins
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Abstract
We studied the nonlinear absorption properties of tetrabenzporphyrins (TBP). Two dimensional delocalized pi- electron systems such as the macrocyclic dyes tetrabenzporphyrins exhibit nonlinear absorption. Their nonlinear absorption and refraction are due mainly to a mechanism that involves the formation of large populations of excited states. This takes place in the spectral regions between B and Q bands. The relevant time frame in which the nonlinear absorption takes place is determined by the dipole dephasing times in the case of the excited singlet states (which is of order picosecond). TBPs have been proposed as candidates for applications in optical power limiting. We have monitored the nature of the nonlinear absorption of TBP samples with picosecond laser pulses at 532 nm wavelength. Open aperture picosecond Z-scan measurements obtained with solutions of TBP in tetrahydrofuran (THF) exhibit reverse saturable absorption (RSA). Our experiments also reveal RSA for a thin film of TBP in a polymethyl methacrylate (PMMA) matrix. On the other hand we observed that for films deposited using the Langmuir-Blodgett (LB) technique the RSA is decreased. A simple extrapolation of solution measurements to thin film samples might result in erroneous conclusions. We investigated the nonlinear absorption of TBP in THF-water mixture to elucidate the role of molecular aggregates in the nonlinear properties of TBP samples. The RSA observed in the case of THF solutions is lost in the mixture.
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Francisco J. Aranda, Francisco J. Aranda, Desai Narayana Rao, Desai Narayana Rao, Devulapalli V. G. L. N. Rao, Devulapalli V. G. L. N. Rao, Masato Nakashima, Masato Nakashima, Barry S. DeCristofano, Barry S. DeCristofano, } "Nonlinear absorption of tetrabenzporphyrins", Proc. SPIE 2853, Nonlinear Optical Liquids, (7 October 1996); doi: 10.1117/12.253474; https://doi.org/10.1117/12.253474
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