Resonant Third-Order Optical Nonlinearities of Chloroform Solution and Neat Film of Poly(9,9-dioctylfluorenyl-2,7-yleneethynylene)

Abstract

The third-order nonlinear optical properties of a chloroform solution and a neat film of poly(9,9-dioctylfluorenyl-2,7-yleneethynylene) (PDOFE) were investigated by forward degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of PDOFE were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least three components, i.e., a coherent instantaneous nonlinear response (electronic response) and two slow responses due to the formation of excited molecules for both the chloroform solution and the neat film of PDOFE. The electronic component of molecular hyperpolarizability per repeat unit of PDOFE in the chloroform solution was determined to be ca. (6.2±0.3)×10-31 esu at 388 nm. The third-order nonlinear optical susceptibility of the neat film of PDOFE was estimated to be ca. (1.2±0.1)×10-8 esu at 387 nm.