Z-scan measurements of third-order optical non-linearities in poly(phenylacetylenes)

摘要

Poly(phenylacetylene) (PPA) and poly(p-methoxyphenylacetylene) (PMOPPA) were synthesized by catalytic polymerization of monosubstituted alkynes and were fully characterized by conventional techniques. Linear and third-order non-linear optical properties of polymers solutions were investigated at lambda= 780 nm using a Z-scan set-up equipped with a femtosecond laser source at different operating regimes. A high repetition rate (76 MHz) regime was used to measure the linear and non-linear absorption coefficients by means of thermo-optical effects. Values of the linear and non-linear absorption coefficients were alpha= 4.9 X 10~(-3) cm~(-1) and beta = 1.1 X 10~(-11) cm W~(-1) for PPA and #alpha# = 2 X 10~(-2) cm~(-1) and beta = 2.1 X 10~(-10) cm W~(-1) for PMOPPA. Very low repetition rate (14 Hz) excitation was used to evidence the purely-optical non-linear refractive indexes, that were gamma = 6 X 10~(-18) cm~2 W~(-1) and #gamma# = 11 X 10~(18) cm~2 W~(-1), respectively, for PPA and PMOPPA.