| Experimental and numerical studies of lasing in multiple light scattering media with gain are presented in this thesis. Depending on the dielectric constant spatial distribution is random or periodic, two different kinds of lasers are discussed: the random laser and the photonic crystal laser. This thesis, therefore, is divided into two parts with each discussing one type of laser.; In the first part, we study on random lasers with the resonant feedback from both weakly and strongly scattering media. We choose the colloidal laser dye solutions as our weakly scattering systems, and experimentally demonstrate coherent random laser emission from them. We numerically illustrate the similarity (difference) between the quasimodes of a passive system and its lasing modes under a global (local) pumping. We also investigate the difference in statistics of the random lasing peaks and the stochastic amplified spontaneous emission spikes from the colloidal solutions, therefore distinguish their distinct physical mechanisms.; For random lasing in strongly scattering media, we utilize closely packed resonant scatterers to enhance the scattering strength and lower the lasing threshold. We synthesize monodispersed ZnO spheres to prepare the resonant scattering samples. We measure the transport mean free path by coherent backscattering, and compare the experimental data to the predicted value by Mie theory. We find that the dependent scattering occurs when the scatterers are close to each other and the resonance from each single scatterer is changed. Nevertheless, we show that the resonant scattering indeed lowers the random lasing threshold.; The second part presents our studies on ZnO photonic crystal slab (PhCS) lasers. We design the PhCS structures with a triangular lattice by a band structure calculation. By varying the in-plane lattice constant, the air cylinder radius, and the ZnO slab thickness, we optimize the in-plane bandgap near ZnO maximum gain frequency. We fabricate the structures with FIB etching technique, and realize single mode lasing at room temperature under optical excitation. Moreover, the lasing wavelength is tuned across a 30 nm wavelength range by varying the lattice constant. The unavoidable fabrication defects can balance the vertical and lateral energy loss and facilitate the lasing. |
