Improved NLO properties through a liquid crystal phase poling



Cross-linkable organic NLO chromophore called DRS was chemically incorporated into silica matrices using the sol–gel process. A number of electrically poled DRS/silica matrix systems were studied to elucidate the relaxation of the oriented organic chromophore by following the decay of UV absorption as a function of time and temperatures. The value of the second harmonic coefficient d33 was 47 pm/V for the DRS/silica matrix films (0.4 μm thickness). From the dramatic decrease in the UV absorption after poling at 80°C, it is speculated that the DRS may act as a liquid crystalline mesogenic group and is effectively oriented in poling at the phase (nematic) transition temperature (80°C). This argument was substantiated by investigating the phase behavior of DRS itself using both DSC and a polarized optical microscope. The DRS/silica system contained the ideal matrices to retain the oriented chromophore because of optical clarity, thermal stability and effective poling at the nematic liquid crystalline phase.