大口径谐振腔式固体激光中的动力学不稳定性研究

Dynamics instability in large-scale resonator based solid-state lasers

大口径谐振腔式固体激光定标到足够高功率后,由于非稳定腔内激光不对称振荡导致介质上激光强度横向不均匀,激光提取与介质产热耦合会引起激光输出功率和光束质量在时域上的不稳定性。针对三种激光器构型:Nd:YAG薄片、Yb:YAG薄片和浸入式液冷叠片激光器,通过理论分析与数值模拟揭示了其各自不同的光热耦合机制及其影响因素,给出了激光输出的瞬态演化规律。结果表明,前两种构型中基于激光动力学的光热耦合具有饱和效应,其动力学不稳定性只出现在特定参数区间,可以通过恰当的设计加以避免;第三种构型中动力学不稳定性表现出明显的阈值特征,在强光状态下只能通过减少冷却液吸收系数来抑制。

Similar with the mode instability in high-power fiber lasers induced by multimode interference and optical-thermal coupling,the output power and the beam quality of large-scale resonator based solid state lasers turn out to be irregularly temporal jitter along with high output power.This phenomenon is mainly due to medium intensity inhomogeneous which results from asymmetric laser oscillation within the unstable resonator and coupling between laser extraction and medium heat generation.For three different laser types,Nd：YAG thin-disk laser,Yb：YAG thin-disk laser and immersed liquid-cooled disk laser,theoretical analysis and numerical simulation are conducted in order to provide basic rules of laser output and distinct optical-thermal coupling mechanism.The results show that dynamics instability only appears within a certain interval since the dynamics presents saturation effects for the former two kinds of lasers.Thus,the instability can be avoided by choosing proper parameters.But for immersed liquid-cooled disk laser,it has obvious threshold under strong optical intensity,dynamics instability can be suppressed only by lower cooling absorption coefficient.