1.电磁透镜 电磁透镜---一 原理 透射电子显微镜中用磁场来使电子波聚 焦成像的装置是电磁透镜。 电磁透镜的聚焦原理示意图
1.电磁透镜 ◆ 电磁透镜----原理 透射电子显微镜中用磁场来使电子波聚 焦成像的装置是电磁透镜。 A C O O’ Z 电磁透镜的聚焦原理示意图
Performance of electromagnetic lens If our own eye lens was as good as our best electromagnetic lens,then we'd be legally blind! 12
Performance of electromagnetic lens 12 If our own eye lens was as good as our best electromagnetic lens, then we’d be legally blind!
Electromagnetic lens p.87 on textbook Electron Source of Soft Fe pole beam electrons pieces. Bore 极靴 Axis Electron trajectory 068086-/.… Focal point Copper windings Cu coils Iron shroud- Gap Magnetic Focus lens field Focal length is determined by field strength: V K:constant based on coil f=K V:accelerating voltage i:mA of current 13
Electromagnetic lens 13 Focal length is determined by field strength: K: constant based on coil V: accelerating voltage i: mA of current 极靴 Bore Gap p.87 on textbook
电磁透镜的焦距可由下式近似计算 N K- 式中K一常数 U,一经相对论校正的电子加速电压 N一电磁透镜激磁安匝数 由上式可知无论激磁方向如何，电磁透镜的焦 距总是正的。改变激磁电流，电磁透镜的焦距和 放大倍数将发生变化。因此，电磁透镜是一种变 焦距或便倍率的汇聚透镜，这是它有别于光学透 镜的一个特点
电磁透镜的焦距可由下式近似计算 式中 K—常数 Ur—经相对论校正的电子加速电压 IN—电磁透镜激磁安匝数 由上式可知无论激磁方向如何，电磁透镜的焦 距总是正的。改变激磁电流，电磁透镜的焦距和 放大倍数将发生变化。因此，电磁透镜是一种变 焦距或便倍率的汇聚透镜，这是它有别于光学透 镜的一个特点。 2 (IN) U f K r L f f M f L L 1 1 2 1 1 1
Magnetic lens Optical lens Electron Light Soft iron pole pieces ↓z Glass lens Convex lens Copper coil中 Electron lens www.globalsino.com/EM/ Inverted and Inverted image rotated image 15
15 Convex lens