Random Laser Bumping Threshold Characteristic Theory

Since 1968, researches on laser emission in random media have been studied formore than forty years. Random laser is a system, which contains a number of elasticscatterers, distributed into the optical gain medium. Multiple light scattering replaces thestandard optical resonator of traditional laser, and interaction between scatter and gaindetermines the laser emission characteristics. At present time, most of random lasers westudied so far are made up of scatterers , which have irregular shape or be distributed.These scatterers take on some average scattering intensity, be constant in the laserfrequency window .Conventional laser is usually constructed from two basic elements: a media whichprovide optical gain, and an optical resonant cavity which limits partial light. In the cavity,when the total gain is greater than the loss, the system reacher a threshold, and lases. It isthe cavity determines the modes of laser, in other words, it determines the direction andfrequency of the laser output. Random laser work on the same principle, however, thefactor determine laser mode is multiple scattering rather than the laser cavity.First of all, we introduced sonme random laser theories, compared with differenttheoretical models to analyze the advantages and disadvantages between them, chose thebest theory as the theoretical basis of this article. Afterwards described the random laserresearch methods in detail, laying the foundation of the analysis for the latter chapters.Around the random laser, we simulated and analysed the random laser emissioncharacteristics of a two-dimensional disordered media which, as well as impact of changescaused by scatter particle parameters on space distribution of random laser localizedmodes. Based on the theory of quasi-state mode, using the finite difference time domainmethod (Finite-Difference, Time-Domain FDTD) to directly solve the Maxwell equationsand rate equations method, taking example for the TM mode, obtained the rules ofquasi-state spacial distribution. With the increasing of radius and refractive index, thefrequencies of quasi-state modes red-shifedt clearly; with the increasing of space density , the frequency of quasi-state modes blue-shifted only al little.