| Diode-laser-pumped monolithic nonplanar ring oscillators (NPRO's) are lasers in which the ring light path defined by the faceted solid-state laser cavity is a closed polygon, the segments of which do not lie in a single plane. When such a laser cavity is immersed in a sufficiently strong magnetic field, unidirectional operation becomes possible, owing to a combination of reciprocal and nonreciprocal polarization effects within the cavity. Unidirectional operation enables the laser to overcome spatial hole burning, so the laser can operate in a single transverse and longitudinal mode. The most important performance feature of such lasers is their excellent short-term frequency stability. In this dissertation I give a complete theoretical description of the eigenpolarization physics of monolithic nonplanar ring laser, including an approach for designing lasers that have low oscillation thresholds and large differential losses between their two internal directions of propagation. Such lasers are ideally suited for use with low power, index-guided diode laser pump sources. Additionally, I present two experimental measurements of the short-term linewidths of diode-laser-pumped monolithic nonplanar ring oscillators. The first measurement describes the heterodyne characterization of two nominally identical, free-running, diode-laser-array-pumped monolithic nonplanar ring oscillators made from Nd:YAG. Under favorable environmental conditions, a heterodyne linewidth of 3 kHz was observed. The second measurement describes the heterodyne characterization of two Nd:GGG NPRO's frequency-locked to the steep sides of successive transmission fringes of a Fabry-Perot reference cavity. The heterodyne linewidth achieved in this later experiment is 500 Hz.; I present plans for improving the active frequency stabilization of these lasers to the subhertz level, and I briefly review means for extending the desirable coherence of master oscillators to higher powers at the master oscillator frequency and to other frequencies via nonlinear optical techniques. Novel laser proposals based on generalizations of the eigenpolarization analysis of monolithic nonplanar ring oscillators are also described. |
