Effects of self-focusing on multiphoton absorption processes in polymer bis-paratoluene sulfonate (PTS)

Summary form only given. The spectral dispersion of multiphoton absorption (MPA) is important in nonlinear optics. For example, two-photon absorption (TPA) reveals the locations of even-symmetry excited states. Previous Z-scan experiments on poor optical quality crystals of bis-paratoluene sulfonate (PTS) have shown, at 1600 nm, the existence of strong four-photon absorption. We have recently developed new crystal growth and polymerization techniques to improve crystal quality substantially. Z-scan experiments have shown much larger MPA than previously and a dependence of the coefficients on a sample thickness. Here we report new measurements of the multi-photon absorption coefficients /spl alpha//sub 5/ and /spl alpha//sub 4/ where /spl Delta//spl alpha/=/spl alpha//sub 3/I/sup 2/+/spl alpha//sub 4/I/sup 3/ and interpret this thickness effect.