In the paper new theoretical aspects of temporal focusing of photoelectron bunch in time-dependent fields are elucidated. The results of computer modeling on electron-optical system with combined time-dependent electric and static magnetic fields which ensure both spatial focusing of the bunch and its temporal compressing up to the subfemtosecond level are presented.
In contrast to the conventional image intensifier with large work area, a streak image tube should possess additional important feature -the comparatively small temporal distortion at the entire work area of the photocathode. With this additional engineering restriction taken into account, a novel small-size meshless streak image tube has been developed by means of numerical optimization. The tube with 25-mm wide work area contains a pair of deflection plates to sweep the electron image along the 25 mm output phosphor screen that is separated by 100 mm from the photocathode. The electron image can be shuttered with a 300 V blanking electric pulse. Electron-optical magnification of the tube is unit; spatial resolution reaches 30 lp/mm over the entire photocathode work area; temporal resolution lies in the 20 -50 ps range, depending on the accelerating voltage (6 -15 kV).
Applied Program Package ELIM I DYNAMICS \ is designed for simulation, optimization and computeraided design of dynamic image tubes with electrostatic focusing and deflection. The Package allows highly precise computation of basic electrical and electron-optical characteristics including spatial/temporal line spread functions, spatial and temporal resolution along the photocathode working area in static and streak modes, spatial and temporal scale distortion, as well as assembling tolerances associated with image errors due to weak disturbances of axial symmetry. One of the main advantages of the new version presented is that "through" computation of electron beam from photocathode to screen is available with regard to dynamic aberrations caused by scattering fields located nearby the edges of deflecting plates. Some examples of image tube computations made with ELIM I DYNAMICS I Package are given.
In this paper, we analyse the applicability of dynamic speckles for distance measurement to any rough surface. The technique is based on spatial filtering of a speckle pattern generated when the object surface is scanned by a laser beam deflected from an acousto-optic device. An extremely short response time was achieved because of the high scanning speed provided by the acousto-optic deflector. We have developed a prototype of the distance-measuring system and studied its performance. The measurement setup has a very simple configuration. The distance can be measured within as short a time as 50 ns, but with rather high inaccuracy caused by the stochastic nature of the speckle effect. The data averaging is easily implemented within a single scan and allows us to achieve an accuracy of 110 µm within the time window of 2.5 µs. An analysis of the factors affecting the performance of the proposed technique is carried out. It is shown that the response time can be diminished by an order of value using an acousto-optic crystal with higher acoustic speed. The proposed technique may be useful for monitoring the geometrical parameters of fast moving or rotating surfaces in various industrial applications.
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