Exploiting birefringent thermal lensing effect to manipulate polarization states of an Nd:YVO₄ self-mode-locked laser

An Nd:YVO₄ laser with a convex-plano cavity is systematically studied to demonstrate the manipulation of output polarization state by using the birefringent thermal lensing effect of the gain crystal. Based on the theoretical analysis of the cavity stability under the influence of thermal lens, the polarization state of output emission is experimentally confirmed that can be controlled to switch from pure π- to pure σ-polarization by simply varying the pump focus position from the tight-focusing to defocusing conditions. More importantly, it is found that there exists an adequate pump focus position within the switching region to lead the π- and σ-polarization to have balanced gain for achieving a stable self-mode-locked laser with orthogonally polarized components. Under the orthogonally polarized mode-locked operation, the pulse repetition rates are found to be 2.23 and 2.33 GHz for the π- and σ-polarization with pulse duration to be 16.1 and 15.1 ps, respectively.