Study On Replica Symmetry Breaking Of Liquid Crystal Laser

Spin glass system is a typical complex system with complex free energy and rich dynamic characteristics.It can be applied to combinatorial optimization,protein structures and neural networks,etc.,therefore,it has great research value.Replica symmetry breaking is an important concept in spin glass theory,which describes the phase transition from paramagnetic regime to spin glass regime.In 2006,Angelani and co-workers first extended the concept of spin glass to the field of optics.After that,many reports have been focused on replica symmetry breaking in solid,liquid and colloidal lasers.Liquid crystal is a kind of material with both crystal anisotropy and liquid fluidity,and different kinds of liquid crystal will have different laser characteristics.This thesis presents whether there is a replica symmetry breaking phenomenon in the liquid crystal laser.The research contents and results are as follows:(1)Research on replica symmetry breaking in nematic liquid crystal random laser.A liquid crystal random laser was prepared by using nematic liquid crystal E7 doped with laser dye PM597 moreover,the random laser spectra were collected under the same experimental conditions,and the change of probability distribution function of emission intensity overlapping parameter under different pump energy was analyzed,so as to observe the phase regime change of random laser.Statistical analysis shows that the replica symmetry breaking appears in the process of pump energy enhancement at 20 ℃.However,the glass state is suppressed and the laser system returns to paramagnetic regime at high pump energy.Additionally,the statistical analysis of laser spectra at different temperatures has been explored due to the influence of temperature on the refractive index and disorder degree of nematic liquid crystal.The results show that temperature will have influence on the phase transition of nematic random laser.(2)Optical properties and applications of cholesteric liquid crystal bandgap laser.In order to verify whether the spin glass theory is suitable for bandgap laser,the optical properties of bandgap laser were studied.Cholesteric liquid crystal laser was prepared by adding chiral agent S811 into E7,it is found that the cholesteric liquid crystal emits bandgap laser at an appropriate temperature.Furthermore,the speckle image of bandgap laser was collected by a CCD,and then the modes of bandgap laser were obtained by calculating the speckle contrast,which proves that the bandgap laser is a multi-mode interaction.Additionally,the bandgap laser and Nd: YAG laser were used as speckle free imaging light source of resolution card respectively,it was found that bandgap laser is a high-quality speckle free imaging light source.(3)Study on replica symmetry breaking in cholesteric liquid crystal bandgap laser.In order to perform the optical intensity fluctuation characteristics of bandgap laser,we collected the bandgap laser spectra at different temperatures,and analyzed the intensity fluctuation at different pump energies by using the replica method.The experimental results show that the fluorescence of PM597 doped cholesteric liquid crystal is in paramagnetic regime when the pump energy is lower than the threshold.The bandgap laser is in glass regime when the pump energy is higher than the threshold,which indicates that there is replica symmetry breaking in the process of pump energy increasing.The spectral intensity fluctuation of PM597 doped cholesteric liquid crystals at different temperatures was studied,as a result,the symmetry breaking phenomenon existed between 34 ℃ and 39 ℃ were observed.