Random Laser Pump Threshold Characteristics

Random laser has been intensively studied in the international laser field for its unique advantages. One hotspot in the research work of random laser is the study about pumping threshold characteristics which have not been studied well due to short development history. So in this thesis, the pumping threshold characteristics are studied via experiment, theoretical analysis and numerical simulation. First the lasing threshold theory is studied from the diffusion area to the localization area by introducing several length parameters which can characterize random laser. Then for the cases when the pumping power is below and above the lasing threshold, the emission intensity, excitation mode and photo distribution are analyzed from theoretical and experimental level. Additionally, the influence of such factors as disordered medium, pumping sources and external environment on the lasing threshold is discussed.Based on the theoretical model coupling Maxwell's equation with the rate equation of 4 level inverted population, the numerical simulation is made via the FDTD method and MATLAB programs. The simulation results show that 1. With the increase of the pumping rate, both the localization of the electric field and the spectrum mode numbers will change; 2. The lasing threshold decreases by increasing the size or concentration of the scatters; 3. The lasing threshold also decreases by increasing the size of samples or strengthening the sample randomness. All these provide important evidence for optimizing the threshold condition of random laser.