Investigations of third-order nonlinear optical response of poly (p-phenylenevinylene) derivatives by femtosecond optical Kerr effect
By using two-color femtosecond optically heterodyned optical Kerr effect and off-resonant single beam Z-scan methods, we investigated the ultrafast photo-induced birefringence of three poly(p-phenylenevinylene) (PPV) derivatives, MEH-PPV (poly-5-(2-ethylhexoxy)-p-phenylenevinylene)), DO-PPV (poly-(2,5-dioctyloxy-1,4-phenylenevinylene)) and DD-PPV (poly-(2,5-didodecyloxy-1,4-phenylenevinylene)). As the 400 nm laser pulse was near the absorption region of PPV derivatives, an ultrafast rise of optical Kerr signal followed by a slow decay process with lifetime about several hundred picosecond was observed. The magnitudes of the real part of χ(3) for PPV derivatives were calculated to be in the order of 10 -10 esu which was one order of magnitude larger than that in 800 nm OKE case. We assign this enhancement to the populated excited state due to the near-resonant excitation in these PPV derivatives.