This thesis presents the development of CW adaptive solid state lasers which dynamically correct for phase distortions within their cavity by phase conjugation. A fibre based four-wave mixing scheme is investigated but no experimental evidence of any phase conjugation is observed.

This thesis presents a strategy for power-scaling diode-end-pumped solid-state lasers based on Nd:YLF operating on the 1.053μm line whilst retaining, efficient, single-frequency, diffraction limited output, the characteristics of low power operation. This strategy reduces the effects of energy transfer up-conversion (ETU), which can decrease the lifetime of the upper lasing level and increase the heat generated per unit volume within the laser rod, increasing the effects of detrimental thermally related problems such as thermal lensing, stress-induced birefringence and stress induced laser rod fracture. Also a passive technique for mode-hopping-suppression is described, allowing the oscillating frequency within the laser cavity to tune over many axial mode spacings before a mode-hop occurs. In order to de-couple the problems of laser resonator power scaling from the maintenance of robust and reliable single-frequency operation, the Nd:YLF laser oscillator output is amplified via Nd:YLF based amplifier stages. A model is presented of the effects of ETU on thermal lensing and small signal gain within the amplifiers along with projected results for further power-scaling prospects. In order to increase the frequency tuning capabilities of the master-oscillator-power-amplifier (MOPA), it was used to pump a series of cw singly-resonant optical parametric oscillators (SROs) based on periodically-poled lithium niobate. Although SROs are inherently single-frequency they suffer detrimentally from mode-hopping, therefore in the final stages of this thesis, we propose to utilise the novel passive technique for mode-hopping-suppression with the SRO cavities in order to achieve robust and reliable single-frequency output. Theoretical expressions and design strategy for low SRO threshold and efficient slope efficiency are expressed along with detailed analysis of the mode-hopping nature of their output. Preliminary results for cw SROs are presented and details of SRO mode-hopping-suppression are included

This thesis presents a strategy for power and brightness scaling in diode-end-pumped, master-oscillator-power-amplifier laser systems, based on Nd:YVOIssues relating to further power and brightness scaling are discussed as well as the potential applications of these laser sources as pump sources for frequency conversion in optical parametric devices.