Distributed Feedback Effects in Lasers and High Gain Laser Instabilities in Optically Pumped Fluoromethane.

In the first part of this thesis we study the effects of finite Bragg gratings in lasers. The threshold mode structure of distributed feedback (DFB) media in partially filled ring cavities is found. We show that when the mode spacing of the unfilled ring cavity and the distributed feedback structure are not the same, the feedback from the ring cavity can increase the mode selectivity of the DFB laser. The mode structure and dynamics of homogeneously broadened bidirectional lasers are studied. These lasers may induce their own Bragg gratings in the susceptibility through standing wave saturation of the gain medium. The structure of the laser modes when this occurs is studied using the ring-DFB theory, and a Fourier decomposed rate equation model is developed to study the dynamic behavior of these modes above threshold. The model is used to explain experimental results that show large bichromatic splittings in a Rhodamine 6G dye laser and is also applied to the cw pumped ruby laser where it predicts regimes in which regular undamped and irregular damped pulsing can occur. In the second part we study, experimentally and theoretically, the irregular spiking of the output of a far infrared (FIR) CH(,3)F laser pumped by a temporally smooth CO(,2) TEA laser pulse. The FIR laser can lase simultaneously by inversion at 496 (mu)m and by depletion at 452 (mu)m. The FIR laser is first characterized so as to determine appropriate approximations for the model of the system. A semiclassical theory for the two coupled lasing transitions is developed which include the complicated kinetics of the system. Theoretical output pulses found by numerically integrating the coupled transition equations are compared to experimental pulses. Both the experimental and theoretical pulse form show extreme sensitivity to small changes in the system parameters. This sensitivity is shown to arise due to the coupling of the two laser transitions.