Study On The Random Laser Based On The Two-dimensional Waveguide Of Liquid Crystals Induced By External Electric Field

Random laser is a special and new laser which uses multiple scattering to provide optical feedback,and plays an important role in the field that traditional lasers can not play.Liquid crystal random laser attracts people's attention because of its advantages of controllable radiation characteristics.In this thesis,we will focus on the problem of the large attenuation of the radiation intensity when using an external electric field to control liquid crystal random lasing.It is proposed to introduce an electric-field-induced waveguide structure into the dye-doped liquid crystal film with uniform orientation to suppress the large electric-field-induced attenuation effect and design a random laser beam splitter.Then we use the numerical simulation method to analyze the influence of the introduction of the waveguide structure on the random laser.A 6-?m-thick dye-doped liquid crystal cell containing an electrode substrate with etched strip structure as the side wall is prepared.And the structure and electric control variation of the electric-field-induced two-dimensional waveguide structure formed in the etched region is characterized.Then the influence of such electric-field-induced waveguide structure on liquid crystal random laser is demonstrated by analyzing the lateral emission spectrum data from experiment equipment.When the applied AC voltage is greater than the threshold voltage(? 1.0 V),the spectral integral intensity of the lateral random laser pumped from the liquid crystal waveguide region is stronger than that outside the waveguide region.The enhancement gradually increases with the waveguide performance,and finally the spectral integral intensity from the liquid crystal waveguide region increases to 1.5 times of that outside.The finite difference time domain(FDTD)method is used to simulate the beam propagation in a straight and Y-shaped waveguide based on parameters of our used liquid crystal sample.The waveguide structure has a very high binding capacity to the light,which makes the light transmit in strict accordance with the direction of the waveguide.Then,a new kinds of dye-doped liquid crystal cell containing an electrode substrate with etched Y-type structure as the side wall is prepared.And a random laser beam splitter based on the electric-field-induced,Y-type liquid crystal waveguide is designed according to the experiment data on propagation and beam splitting characteristics of He-Ne laser in the Y-type waveguide,combined with the spatial distribution of the lateral random lasing pumped from the liquid crystal waveguide region.FDTD solutions simulation software is used to investigate the influence of scattering particle concentration,refractive index and other factors on the intensity and field energy distribution of the existing random field in random scattering medium.When the refractive index contrast between scattering material and background is large,the spectrum shows a strong peak mode,and the photon localization degree is larger.When the area of random scattering medium decreases,the number of emission spectrum modes decreases significantly,and single spectrum mode results are possible.Furthermore,the influence of waveguide structure introduced into the random scattering medium on the photon localization and transmission of quasimodes and random laser is studied.With the aid of the waveguide structure,the strong energy region in the random medium is concentrated near the waveguide structure,making the output beam propagate in the random scattering medium directionally.