Photoinduced nonlinear optical effects in 1,4-cis-polybutadiene polymers

Photoinduced nonlinear optics phenomena in 1,4-cis-polybutadiene have been investigated. Both an external electrostatic field as well as UV laser photoinducing light lead to enhancement of the local non-centrosymmetry determining optical second harmonic generation (SHG). Using nb initio quantum chemical calculations and experimental nonlinear optics data we have shown that there exist values of the external fields corresponding to the maximal SHG values. Low-temperature ordering (below 10 K) (due to decrease of thermoreorientation) and hydrostatic pressure-induced strength also favour photoinduced SHG. Time-resolved SHG measurements indicate an existence of at least two short-time components (about picosecond range), that may be caused by different mechanisms of the observed phenomenon. It has been shown both experimentally and theoretically that the degree of non-centrosymmetry for the corresponding butadiene bonds is closely connected with the UV-photoinducing power, temperature, hydrostatic pressure and delaying time between the photoinducing and probing beams.