The Numerical Simulation Of2D Random Medium(ZnO) Laser On The Spatial Distribution And Output Characteristics Of Frequency Spectrum

The traditional laser is mainly composed of optical gain medium and feedback mechanism of the optical cavity, where the coherent optical feedback is formed from the optical resonator feedback amplifier. Different from the traditional laser mechanism, the generation of random laser is disorderly. Random scattering particles constitute a closed loop for laser amplifier and provide a positive feedback effect. Based on the unique characteristics and physical mechanism, random laser phenomenon is widely researched in recent years. Early random medium is mainly TiO2particles. In recent year, ZnO particles attract people’s interesting and are applied in the study of random laser due to its unique characteristics. At present, the research on the random laser is mainly based on the Anderson localization theory and quasi state model of modulus theory.In this dissertation, according to the Anderson localization theory and quasi state model theory, two-dimensional coherent feedback random lasers (ZnO) are numerical simulated. The evolution of the laser modes and output characteristic spectral features are obtained using the computing software MATLAB. The main work includes the following aspects of content:1. Finite difference time domain method (FDTD) was introduced in detail in the numerical simulation. Some important details were discussed in the model, including the excitation source, the PML absorbing boundary condition, numerical stability condition and the gain medium model.2. Based on the Anderson localization and quasi state mode theory of random lasers, the spatial distribution and output characteristic spectral features of two-dimensional random lasers (ZnO) are studied in detail. The simulation results show that the pumping light would form a spherical wave propagating around the light source after a short time. With the evolution of calculation of time, most of the energy was gradually localized due to the multiple scattering by disordered dielectric particles and localized in a particular area. The localized area became concentrated gradually compared to the scattered phenomenon in the beginning. As results, the sharp laser radiation phenomenon was formed.3. Wave propagation and the influence of output spectrum were studied under the different filling rate of the random medium. As can be seen from the results, spectrum characteristics of random laser were not changed, but convergence time, expansion area of localized modes, and the size of the output spectrum energy was different. Similarly, the influence of pump wavelength and the refractive index were studied.Accordingly, the phenomenon of laser radiation was random medium and the interaction between the pump matching the overall scattering effect of the results. Through the numerical simulation results show that, the wavelength of the laser output characteristics would not be affected with the pump wavelength, and has the stable wavelength phenomenon. These phenomena can be using the theory of quasi state model to explain it more reasonable.