Yakunin S. Nonlinear optical response of the system of liquid crystal doped with organic dye

The results of complex investigation of nonlinear optical (NLO) response and spectral properties of the system of liquid crystal (LC) matrix 4?n-pentyl-4-cyanobiphenyl (5CB) doped with anthraquinone (AQ) dye are presented in the thesis. The photoinduced changes of refractive index and absorption coefficient due to selfaction of the laser beam, absorption spectroscopy of visible and IR ranges, photoluminescence (PL) spectroscopy and third harmonics generation techniques were used. For the first time the PL band at 720 nm with the decay time about 3 ms was observed and its excitation spectrum structure was investigated. Origin of the band is due to quenching of 5CB PL band when the AQ dopant was admixed. It was found the quadric dependence on dopant concentration of real and imaginary parts of cubic NLO susceptibility c(3) of the LC doped with AQ: Re(c(3))~cw2 and Im(c(3))~cw2 under excitation by picosecond laser pulses in the transparency range (l=532 nm) of the system. The obtained dependences can be explained by the cooperative response of the dye subsystem. It was shown the cubic behavior on dopant concentration of real part of c(3): Re(c(3))~cw3 of homeotropic LC cell doped with AQ dye under excitation by continuous wave He-Ne laser beam. The cubic dependence was explained by the response of strongly interacted dye molecules. The sign inversion effect of the cubic NLO response was discovered in planar LC cell doped with AQ dye when the angle between the LC director and excitation polarization changed from 900 down to 00. It was assumed, that the angle with zero value of the NLO response corresponds to the dye molecular aggregates axis direction in LC matrix.