The Study On The Polarization Property Of Light-waves In Two-dimensional Random Media

The research on optical properties of the polarized light-waves in two-dimensional random media has become research hotspot in laser physics. In prior research on the polarization property of the light-waves in the random media, the competition on the population inversion between different polarized states is neglected. It is necessary to have a comprehensive research on the polarization property. The main content of this thesis is summarized as follows.(1) We introduce the principle and arithmetic of Finite Difference Time Domain (FDTD) method particularly, including the excitation sources, the conditions of stability of calculation, and Perfectly Matched Layer (PML) boundary conditions. All of these factors ensure the results are reliable.(2) Based on FDTD method, we create a numerical model for the research on polarization property of the light-waves in two-dimensional random media. And the competition on inversed population between the transverse magnetic (TM) polarization state and the transverse electric (TE) polarization state is investigated. The results indicate that TM state has a larger lasing threshold than that of TE state so that TM state is suppressed strongly by TE state in the competition. The larger the size of the medium is, the easier the lasing modes in TM state appear.These conclusions are different from the results of the case without the competition on inversed population between different polarized states.(3) The threshold property of the two polarization states with local pumping is analyzed. Results show that the lasing threshold of TM modes is lower than that of TE ones when the radius of the local pumping region is suitably selected, and the case would be contrary when the selected radius of the local pumping region is excessive.The conclusion provide an effective method to obtain TM polarized light-waves.(4) Under local pumping, the spectral time evolution of polarized modes is also investigated. And the values of quality factor (Q-factor) are obtained for the selected polarized modes by calculating the decay rates of them. The results demonstrate that there exists a critical value of local pumping area for TM modes. If the area is less than this value, the TM modes would have a quicker rising of the peak intensity and smaller Q-factor than that of TE modes. Or else, the conclusions would be contrary.(5) Compare with the prior research, the spectrum for two polarized states with the competition on inversed population in a set of two-dimensional (2D) active random media is calculated. And these random media have same random constitution but different shapes. Results show both two polarized states are morphology dependent and the variety of the shapes has more influence on the selection of TM polarized modes than that of TE polarized modes. Appropriate design of the shapes has obvious effect on the selection of TM polarized modes and can improve the adverse situation of TM polarized state in the competition. Such polarization-dependent difference of morphology property presents a new mode-selecting technique for random lasers.