Holographic laser resonators
The work presented within this thesis details the development and characterisation of a CW solid-state adaptive resonator that uses phase-conjugation to actively correct for phase distortions present within the resonator loop. It is shown that the phase-conjugate of a given beam can be produced by the process of degenerate four-wave mixing inside a gain medium. In this scheme two mutually coherent beams overlap within a population inverted region of a laser amplifier and the subsequent interference pattern between them spatially hole burns a grating into the gain. The diffraction efficiency of such gain-gratings is studied both theoretically and experimentally and it is shown that, due to the stored inversion, CW phase-conjugate reflectivities of greater than 100 can be achieved in Nd:YVO4. Using this gain four-wave mixing scheme an adaptive resonator is built that is capable of oscillating with a phase-conjugate mode. The ability of the volume gain-grating to encode and react dynamically to phase distortions present within the resonator loop ensures that the phaseconjugate output beam from the resonator always remains a faithful reproduction of the beam used to seed the resonator. The interactions occurring within the resonator are modelled and a resonator capable of producing an 11.6 W near-diffraction limited output is demonstrated. The powerscaling capabilities of such lasers is then considered and it is shown that the output power can be increased whilst maintaining phase-conjugate oscillation. It is shown that a phase-conjugate output of 6 W can be scaled to 11.7 W with the addition of a power amplifier placed into the existing setup.