Stochastic Effects in Single and Multimode Lasers.

This thesis is concerned with experiments related to the development of a ring dye laser system and an investigation of the noise characteristics and dynamics of the laser, when operated in one or two modes. The design and construction of the laser is described. A variable transmission output coupler and tuner was invented that provides independent control of the output power and wavelength of the ring laser, without appreciable deviation of the output beam. It also allows optimization of the laser output at a given wavelength and extension of the lasing range over that normally obtainable. The basic laser equations are reviewed, and algorithms for the simulation of the stochastic differential equations are described. These algorithms are tested by comparisons with exact analytic results that are available for the Kubo oscillator. We report that the conventional algorithm for simulation of multiplicative white noise processes is flawed; however, the colored noise algorithm may be successfully used even in the white noise limit. Our experiments on the noise characteristics of the ring laser when operated in the steady state demonstrated clearly that the dominant source of intensity noise is the pump noise from the argon laser. Computer simulations and an approximate linearized theory show good agreement with experiments. The dye laser is found to act increasingly as a low pass filter for the fluctuations of the pump laser as it is operated progressively closer to threshold. This pump noise acts as a probe of the critical slowing down of the dye laser as it approaches threshold. Experiments on the transient dynamics of the ring laser result in a technique to determine the effect of the quantum and external noise sources on the growth of the laser radiation from a spontaneous emission background. These experiments, based on the measurement of first passage times for the laser intensity, are applied to a single longitudinal and transverse mode laser, and then to a laser with two transverse modes. We describe the passage time distributions measured, and compare them to computer simulations. This is the first study of the stochastic dynamics of transverse modes in a laser. (Abstract shortened with permission of author.).