Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external opticalfeedback on the polarization state of longitudinal modes inquasi-isotropic microchip Nd:YAG lasers. Under optical feedback, thepolarization state of longitudinal modes in quasi-isotropic lasersrelies strongly on the intracavity anisotropy loss and modecompetition. When the intracavity anisotropy loss is small, externaloptical feedback can cause polarization switching and strong modecompetition between two orthogonal linearly polarized eigenstates ofone laser longitudinal mode, which leads to the distortion of laserintensity modulation waveform. The polarization switching isindependent of the initial external cavity length. By increasing theintracavity anisotropy loss, one polarization eigenstate can besuppressed and the laser works in single-polarization state. Atheoretical analysis based on the compound cavity model ispresented, which is in good agreement with the experimental results.The results offer guidance to the development of laser feedbackinterferometers.