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 phot oinducing light lead to enhancement of the local non-centrosymmetry determi ning optical second harmonic generation (SHG). Using nb initio quantum chem ical 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 thermore orientation) and hydrostatic pressure-induced strength also favour photoind uced SHG. Time-resolved SHG measurements indicate an existence of at least two short-time components (about picosecond range), that may be caused by d ifferent mechanisms of the observed phenomenon. It has been shown both expe rimentally and theoretically that the degree of non-centrosymmetry for the corresponding butadiene bonds is closely connected with the UV-photoinducin g power, temperature, hydrostatic pressure and delaying time between the ph otoinducing and probing beams.