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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 diffraction integral theory describing the propagation of light beams, the three-dimensional near-field and far-field light intensity distributions of the non-steady-state DF laser were simulated using the Fast Fourier Transform algorithm. The simulation results show that the near-field output spot shape of the unstable cavity is a hollow ring centered symmetrically and the far-field output spot is a multi-order diffraction ring with a center bright spot. The large M number will cause the near-field light spot energy to be concentrated, and the large Neq The value will cause the far-field divergence angle to become larger. The algorithm was used to study the influence of the tilt of the endoscope on the near-field light intensity distribution: the tilting of the endoscope made the near-field distribution of the light beam worse, and the larger the tilt angle, the more obvious the asymmetrical distribution of the light intensity. Uncooled cavity uniaxial DF laser experiments were carried out. The near-field and far-field light intensity distributions and near-field speckle changes of the uncooled DF laser were consistent with those of the numerical simulation. The experimental far-field divergence angle was 1.2 mrad. The simulation results in this paper can provide the basis for diagnosing and adjusting the laser cavity misclassification of DF laser.