Calvo M
Instituto de Física, Universidad Católica de Valparaíso, P.O. Box 4059, Valparaíso, Chile.
Ultramicroscopy. 2004 May;99(2-3):179-87. doi: 10.1016/j.ultramic.2004.01.001.
We analyse the optimal conditions for operation of a time-dependent magnetic field lens recently proposed. The lens consists of an axially symmetric ellipsoidal coil producing a spatially homogeneous but time-pulsating magnetic field. This system is capable of focusing a beam of charged particles drifting parallel to the coil axis as well as forming images of an object emitting electrons. This lens has no spherical aberration and, consequently, opens the possibility of surpassing the resolving power of conventional round static field lenses. The cardinal elements of this lens are functions of time and thereby the image position, its magnification factor and orientation change in time. We show how by a suitable choice of the magnetic field pulse parameters and the introduction of screens with circular apertures, it is possible to render all the image characteristics stationary. The effect of diffraction is also discussed in the context of transfer function theory.
我们分析了最近提出的时变磁场透镜的最佳运行条件。该透镜由一个轴对称椭圆形线圈组成，可产生空间均匀但随时间脉动的磁场。该系统能够聚焦平行于线圈轴漂移的带电粒子束，也能形成发射电子的物体的图像。这种透镜没有球差，因此有可能超越传统圆形静电场透镜的分辨能力。该透镜的主要元件是时间的函数，因此图像位置、放大倍数和方向会随时间变化。我们展示了如何通过适当选择磁场脉冲参数并引入带有圆形孔径的屏，使所有图像特征保持稳定。还在传递函数理论的背景下讨论了衍射的影响。
