Optik 122 (2011) 287–294
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Optik
journal homepage: www.elsevier.de/ijleo
Static and dynamic imaging electron optics and spatial–temporal aberrations in a
bi-electrode spherical concentric system with electrostatic focusing
Li-wei Zhou
a,∗
, Hui Gong
a
, Zhi-quan Zhang
b
, Yi-fei Zhang
b
a
Beijing Institute of Technology, Beijing 100081, PR China
b
Institute of Armored Force Engineering, Beijing 100072, PR China
article info
Article history:
Received 15 August 2009
Accepted 5 January 2010
Keywords:
Static electron optics
Dynamic electron optics
Paraxial and geometrical lateral aberrations
Paraxial and geometrical temporal
aberrations
A bi-electrode concentric spherical system
with electrostatic focusing
abstract
In imaging electron optics, for a concentric spherical system composed of two spherical electrodes with
electrostatic focusing, the electrostatic potential distribution and the spatial–temporal trajectory of elec-
tron motion can be expressed by analytical forms. It is naturally to take such system as an ideal model
to investigate the imaging properties, as well as the spatial–temporal aberrations, to analyze its partic-
ularity and to find the clue of universalities and regularities. Research on this problem has important
significance, which can afford theoretical foundation not only in studying static electron optics for the
night vision devices, but also in studying dynamic electron optics for high-speed image converter tubes.
In the present paper, based on the practical electron ray equation and electron motion equation for
a bi-electrode concentric spherical system with electrostatic focusing, the spatial–temporal trajecto-
ries of moving electrons emitted from the photocathode have been solved, the exact and approximate
formulae for image position and flight time of electrons, have been deduced. Start from solutions of
spatial–temporal trajectories, the electron optical spatial–temporal properties of this system are then
discussed. According to the definitions of spatial–temporal aberrations, the paraxial and geometrical lat-
eral aberrations, as well as the paraxial and geometrical temporal aberrations, have been deduced, that
are classified by the order of
√
ε
z
/
ac
and
√
ε
r
/
ac
.
© 2010 Published by Elsevier GmbH.
1. Introduction
For an electron optical imaging system, spatial-trajectory-spread and transit-time-spread produced by initial emission energy and
initial emission angle of photoelectrons are the fundamental problems of image tubes and high-speed image converter tubes. In the static
mode operation for these two tubes, the spatial-trajectory-spread of electron trajectories at the image plane determines limited spatial
resolution. In the streak mode operation for high-speed image converter tube, a point image of a photo event of very short duration is
imaged by the camera as a line because of transit-time-spread. The length of the line is proportional to the transit-time-spread. Obviously,
the shorter the length of the line, the better the time resolution of the camera.
It was proven that the spatial-trajectory-spread of an imaging system is mainly determined by the paraxial lateral aberration of second-
order, which is usually summarized as Recknagel–Artimovich formula [1,2]. Formula shows that the paraxial lateral aberration of second-
order does not depend on the concrete electrode structure and potential distributions, but depends on initial electron emission energy,
the strength of electric field at the photocathode, the linear magnification of the system and the position of image plane.
Similarly, the transit-time-spread of an imaging system is mainly determined by the paraxial temporal aberration of first-order, which
is expressed by Savoisky–Fanchenko formula [3]. Formula shows that the temporal aberration of first-order depends only on the initial
emission energy, the strength of electric field at the photocathode, but does not depend on the concrete electrode structure and potential
distribution. Besides, it does not depend on the linear magnification of the system and the position of image plane.
Thus, we may find many similarities between Recknagel–Artimovich formula and Savoisky–Fanchenko formula, but the difference
exists. We can also find the non-harmonious and non-symmetry between them if we think it over. Actually, either the spatial-trajectory-
spread or the transit-time-spread at an image plane, which are produced by spatial–temporal trajectories emitted from photocathode with
∗
Corresponding author at: Beijing Institute of Technology, School of Information Science and Technology, 5, Zhongguancun South Avenue, Haidian Zone, Beijing 100081,
PR China. Tel.: +86 10 68911748; fax: +86 10 68912550.
E-mail address: zhoulw@vip.sina.com (L.-w. Zhou).
0030-4026/$ – see front matter © 2010 Published by Elsevier GmbH.
doi:10.1016/j.ijleo.2010.01.003