非链式DF激光器非稳腔数值仿真与实验

Numerical simulation and experiments on unstable resonator for non-chain DF laser

基于描述光束传播的菲涅耳-基尔霍夫衍射积分理论,运用快速傅里叶变换算法仿真了非稳腔DF激光的三维近场、远场光强分布。仿真结果显示:非稳腔的近场输出光斑形状为中心对称的空心圆环,远场输出光斑为具有中心亮斑的多级衍射环;大M数将导致近场光斑能量集中,大的Neq值将引起远场发散角变大。运用该算法研究了腔镜倾斜对近场光强分布的影响:腔镜倾斜使光束近场分布变差,倾斜角越大,光强的非对称分布越明显。开展了非链式DF激光器非稳腔实验研究,实验得到的近场、远场光强分布及腔镜失调下的近场光斑变化情况与数值模拟结果一致,实验测量的远场发散角为1.2 mrad。文中的仿真结果可为DF激光器腔镜失调诊断及调节提供依据。

Based on the Fresnel-Kirchhoff＇s integral theory, the three-dimensional near filed and far filed light intensity distribution of non-chain pulsed DF laser with unstable resonator was obtained using Fast Fourier algorithm. Numerical calculation shows that the mode pattern is ring shaped at near field and multistage diffraction ring with central bright spot at far field, and the near field spot laser intensity will be concentrated as M increases, while the far field angle of divergence will increase with the increment of effective Fresnel number （Neq）. Then the influence of mirror tilt on near-field light intensity distribution is investigated, indicating that the beam in near field will be deteriorated when misalignment appears, the larger of the tilt angle the much more obvious of asymmetric light distribution. The measured light intensity distribution on near-field and far-field and the variation of near filed light intensity distribution with mirror tilt angle are consistent with the simulation results, and the far-field divergence obtained is 1.2 mrad. The simulation results can provide a basis for cavity mirror misalignment diagnostic analysis and resonator regulation of non-chain DF laser.