Gain-grating analysis of a self-starting self-pumped phase-conjugate Nd:YAG loop resonator

We investigate both experimentally and theoretically the contribution of the different gain gratings in a self-starting self-pumped phase-conjugate Nd:YAG loop resonator. Thanks to a transient model, we show that the transmission-grating configuration is more efficient than the reflection-grating configuration, and that their temporal dynamics are different, in agreement with the experiment. Maximum extraction is obtained for the four-grating configuration. The output beam is a high-quality diffraction-limited TEM₀₀ mode, even with severe intracavity phase aberrations, and has a single-longitudinal-mode pulse shape of ~13 ns, with maximum energy of ~130 mJ up to 30 Hz. We also investigate the role of the output coupler reflectivity on the output pulse energy and formation. Finally, the influence of the different gratings on the ability of such a self-starting loop resonator to correct for polarization distorsions is studied