MOLECULAR 2ND HYPERPOLARIZABILITY MEASURED IN CUMULENE-CONTAINING POLYMERS

Nonlinear optical susceptibilities were measured in a cumulene-contain ing polymer using the Z-scan technique at 1064, 780 and 590 nm, respec tively. At off resonance conditions we obtained real (Re) and imaginar y (Im) orientationally averaged second hyperpolarizability gamma from a straightforward Z-scan analysis using CS2 as our standard; we got Re gamma=-6.2 x 10(-30) esu at 1064 nm, and gamma=(-2+0.26i) x 10(-30) e su at 780 nm. Measurements at 590 nm were accompanied by one-photon ab sorption saturation, which could be mathematically extracted from the overall gamma, leaving only the nonresonant terms. We thus obtained at 590 nm gamma=(-1.4+2.2i) x 10(-29) esu. The two orders or magnitude i ncrease in Im gamma from 780 to 590 nm is discussed within the summati on of states model.