WIEN FILTER - A WAVE-PACKET-SHIFTING DEVICE FOR RESTORING LONGITUDINAL COHERENCE IN CHARGED-MATTER-WAVE INTERFEROMETERS
WIEN FILTER - A WAVE-PACKET-SHIFTING DEVICE FOR RESTORING LONGITUDINAL COHERENCE IN CHARGED-MATTER-WAVE INTERFEROMETERS
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DOI：
10.1103/physreva.48.152
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发表时间：
1993-07-01
影响因子：
2.9
通讯作者：
HASSELBACH, F
中科院分区：
文献类型：
--
作者：
NICKLAUS, M;HASSELBACH, F
双光束干涉仪的纵向相干性是指两个部分波包同时到达干涉面。在带电粒子干涉仪中，由于几何路径长度的差异，光路长度的差异，或者部分或全部光束路径上两个波包的群速度的差异，这种同时性可能会丢失。这些影响中的几个可以结合在一起产生干涉平面中波包之间的净相对空间延迟，从而导致干涉条纹对比度的降低。在带电物质波干涉测量中，可以使用维恩滤波器来补偿这种相对延迟，从而重建纵向相干性。维恩滤波器由相互垂直的电场和磁场以及光束路径组成。在其匹配状态下，即当静电和电子上的磁力完全相互抵消时，维恩滤波器既不会使光束偏转，也不会对波包施加任何相移。然而，在横向分离的路径上通过维恩滤波器的波包在不同电位的区域传播，并且反过来以不同的群速度传播，这导致波包相对于彼此的纵向位移。通过选择由维恩滤波器引起的补偿延迟与上述影响引起的净相对延迟完全相反，可以恢复最大的纵向相干性（从而恢复条纹对比度）。实验证明了维恩滤波器的这一特性。本文讨论了电子能谱中不同波长的平面波在配准面上的非相干叠加现象，讨论了维恩滤波器的相干恢复作用。它证明了描述粒子系综的波包中自干涉平面波分量的量子力学相干性比干涉条纹对比的实验损失通常所表明的更强。这种对比度恢复装置的可用性对于极低能量（几个keV或更少）电子干涉测量尤其重要。它也可能成为未来离子束干涉仪的重要组成部分。
Longitudinal coherence in two-beam interferometers means that the two partial wave packets arrive in the plane of interference simultaneously. In charged-particle interferometers, this simultaneity can be lost due to a difference in the geometrical path lengths, a difference in the optical path length, or a difference in the group velocities for the two wave packets on parts of or all of the beam paths. Several of those influences can combine to yield a net relative spatial delay between the wave packets in the interference plane, thus causing a reduction of the interference fringe contrast. A Wien filter can be used in charged-matter-wave interferometry to compensate for this relative delay and thus to reestablish longitudinal coherence. A Wien filter consists of an electric and a magnetic field perpendicular both to each other and the beam path. In its matched state, i.e., when the electrostatic and the magnetic forces on the electrons exactly cancel each other, the Wien filter neither deflects the beams nor exerts any phase shift on the wave packets. However, wave packets traveling through the Wien filter on laterally separated paths propagate in regions of different electric potentials and in turn with different group velocities, which leads to a longitudinal shift of the wave packets relative to each other. Maximum longitudinal coherence (and thereby fringe contrast) can be restored by choosing the compensating delay caused by the Wien filter exactly opposite to the net relative delay caused by the influences mentioned. An experiment is presented that demonstrates this property of a Wien filter. The coherence-reviving action of a Wien filter is discussed in the context of the incoherent superposition in the registration plane of the plane waves corresponding to different wavelengths in the electron spectrum. It demonstrates that the quantum-mechanical coherence of the self-interfering plane-wave components of the wave packets describing the particle ensemble is more robust than the experimental loss of interference-fringe contrast often suggests. The availability of such a contrast-restoring device is especially important for very-low-energy (a few keV or less) electron interferometry. It is also likely to become important for future ion-beam interferometers.