Effect Of Different Alignment Methods On Dye-doped Liquid Crystal Random Laser

Based on the scattering properties of liquid crystals in the dye-doped liquid crystal random lasers,the effects of different photoalignment methods on the anisotropy of liquid crystals are discussed in the dye-doped liquid crystal random lasers.After introducing the research background of random lasers,the scattering analysis of liquid crystal systems and the development of photoalignment technology,this paper puts forward the research of the effects of different photoalignment on dye-doped liquid crystal random laser.The fabrication of dye-doped liquid crystal random laser with a sandwich structure based on optical functional film is designed,which presents good optimization effect on the threshold energy of the dye-doped liquid crystal random laser and improves the radiation intensity of the dye-doped liquid crystal random laser.The mixture of polymer and azo dye is coated on the glass substrate,made into optical function film after photoalignment,then liquid crystal and laser dye mixture solution is added to create a liquid crystal cell with a sandwich structure.The polarized light microscope image of the liquid crystal cell is tested,which provides evidence for the good orientation effect of the optical functional film.The effect of optical functional films made of PVA aqueous solutions with different mass fractions on random lasers is reported.When the PVA mass fraction is 10.0wt%,the random laser threshold energy reaches the lowest(2.4 m J/cm~2),which is reduced by 55.6%compared with the random laser threshold(5.4m J/cm~2)without optical functional film.Under this condition,the optical functional film is coated uniformly,and achieves good photoalignment effect on liquid crystal.The equivalent cavity length of the random laser is calculated by power Fourier transform spectroscopy of the random laser spectrum,which proves that the optical functional film provides the multiple scattering and gain volume required by the random laser.As the feasibility of dye-doped liquid crystal random laser with optical function film is achieved,a dye-doped liquid crystal random laser with optical function film using multiphoton absorption characteristics is subsequently designed.For the way of photoalignment on polymer-dispersed liquid crystal,a method of adjusting the p H of the azo dye methyl red solution to change the absorption peak is proposed,so as to select the suitable light wavelength to make methyl red cis-trans isomerization induces the photoalignment of liquid crystal molecules.Firstly,the absorption peak position of the azo dye methyl red after changing the p H and the absorption spectrum and fluorescence emission spectrum of the laser dye PM597 are measured.The light with the appropriate wavelength are selected for the photoalignment and pumping process.After the liquid crystal cell is prepared,the polarizing microscope is used to test the photoalignment effect.The threshold of the random laser emitted by the dye-doped liquid crystal random laser with methyl red in basic form(p H=9.00)(1.6m J/cm~2)is better than that of methyl red in the neutral form(p H=4.98)(5.4m J/cm~2)decreased by 70.4%.The spectrum of the random laser of methyl red in basic form(p H=9.00)and the calculation of the scattering MFP prove that strong scattering occurs in the sample,generating coherent random laser.This method presents good photoalignment effect on liquid crystal,enhances the scattering intensity of the polymer-dispersed liquid crystal system and improves the pumping efficiency of the laser dye PM597,thus obtaining random laser with lower threshold.