INVESTIGATION OF ATOM IMAGING BY ELECTRIC FIELD

聚焦透镜是原子光学不可缺少的组成部分。实现凸透镜的常用方法是近谐振光的衍射和微细加工的透明干涉结构。我们利用电场来实现凸透镜。处于稳定状态的原子的斯塔克效应是负的。因此，原子被拉向电场强度的局部最大值。虽然在自由空间中不可能产生局部最大静电场，但微波场可以。利用TM010模式的柱面微波腔，对由亚稳态霓原子陷阱产生的慢霓原子束进行聚焦。TM010模场的径向变化是0阶贝塞尔函数，且在轴上有一个极大值。腔的直径与频率成反比。然而，聚焦功率与频率的立方成正比。因此，使用可以传输整个原子束通过腔的最高频率是有利的。我们使用17 GHz的微波炉。腔体的直径和长度分别为13 mm和13 cm。腔体的Q值约为6000。速度较慢的原子垂直下落。腔体下方的原子束图案由微通道探测器探测，该探测器可以产生分辨率约为50微米的二维图像。在腔体下方60 cm处观察到了清晰的聚焦，微波功率为13.5W。

Focusing lenses are indispensable components of atom optics. Popular methods of realizing convex lenses are diffraction by near resonant laser light and by micro-fabricated transparent interferometric structures. We use electric field to realize a convex lens. The Stark effect of atoms in a stable state is negative. Therefore, atoms are pulled towards the local maximum of electric field intensity. Though it is not possible to generate a local maximum of static electric field in free space, microwave field can. We use a cylindrical microwave cavity in TM010 mode to focus a slow neon atomic beam that is generated from a trap of metastable neon atoms. The radial variation of the electric field of the TM010 mode is the 0th order Bessel function and has a maximum on axis. The diameter of the cavity is inversely proportional to the frequency. However, the focusing power increases proportional to the cube of the frequenct. Therefore, it is advantageous to use the highest frequency that can transmit entire atomic beam through the cavity. We use 17GHz microwave. The diameter and the length of the cavity are 13mm and 13 cm, respectively. The Q value of the cavity was approximately 6000. The slow atoms are vertically dropped. The pattern of the atomic beam below the cavity is detected by a micro-channel detector that can produce two-dimensional image with the resolution of approximately 50 micron meters. A clear focusing was observed at the distance 60cm below the cavity with the microwave power of 13.5W.