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Applied Physics B, November 2012, Volume 109, Issue 2, pp 201-209.
B. Bhushan, S. K. Kumar, S. S. Talwar, T. Kundu, B. P. Singh.
Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India.
Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India.
Abstract
We have investigated the spectral dispersion of second molecular hyperpolarizability {Gamma} (−ω′; ω, −ω,ω) of three derivatives of heteroarylene methine by antiresonant ring interferometric nonlinear spectroscopic technique using femtosecond modelocked Ti:sapphire laser in the spectral range of 725–820 nm. The observed dispersion of {Gamma} has been explained in the framework of three-essential states model involving the ground state, a one-photon excited state and a two-photon excited state. The spectral response of the hyperpolarizability has been correlated with the electronic and chemical structures of the three derivatives of heteroarylene methine. The estimated {Gamma} values have been compared to the fundamental quantum mechanical limit. We have found for the first time that the heteroarylene methines approach this limit within a factor of 2 while even the best known molecule so far falls short of this limit by a factor of 30.
