具有夹层极靴的新型电子探针透镜的设计与计算

The Design and Calculations of a New Probe Forming Lens with Sandwich Pole Pieces

本文分析讨论了具有夹层极靴的新型探针透镜的设计计算方法。提出采用轴上线性增长线性下降的似优磁场分布,在工作距离给定后,仅用两个场形参量就可以唯一地确定透镜的场形,并可以获得近似最小的球差系数。本中从模型场出发,导出了夹层极靴的设计计算公式,介绍了它的计算机辅助设计方法。用所述方法设计的一个实际透镜,在工作距离L_s=30mm时,球差系数C_s=84mm,色差系数C_c=64mm,激励(NI)/((V_r)^(1/2))=8.0.在试样上方有50°的自由空间角。

A design procedure is described for the new sandwich pole piece forming lens.lt is pointed out that having adopted a similar optimal model distribution composed of a linearly rising part followed by a linearly falling part,the length of the lens and the slopes of the two parts of the field are solely determined by the working distance provided a minimum in C_s is imposed as a requirement.The resulting design can yield very loW spherical aberration constants at long working distances.A practical leis was designed based on principles and procedures described above.At a workiag distance of 30mm,the C_s=84mm and C_=64mm.50° of free space above the spcimn was left unobstructd by the lens.