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Electron Beam Pulsing by Optoelectronically Switched Electron Gun

IP.com Disclosure Number: IPCOM000062361D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Jenkins, KA: AUTHOR

Abstract

In stroboscopic electron beam testing, the time resolution is determined by the length of the electron beam pulse and the control of its start time. Conventional electrostatic beam chopping can be used to make pulses about one nanosecond long; shorter pulses can only be obtained with great difficulty [1]. Also, simple beam chopping reduces the net usable beam by the duty cycle. The technique described herein will easily make pulses as short as 100 picoseconds, with excellent control of the start time, and gives 10 or more times the beam intensity of conventional chopping. The technique uses pulsed voltages on both the Wehnelt grid and the anode of a typical electron gun, as shown in the drawing.

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Electron Beam Pulsing by Optoelectronically Switched Electron Gun

In stroboscopic electron beam testing, the time resolution is determined by the length of the electron beam pulse and the control of its start time. Conventional electrostatic beam chopping can be used to make pulses about one nanosecond long; shorter pulses can only be obtained with great difficulty [1]. Also, simple beam chopping reduces the net usable beam by the duty cycle. The technique described herein will easily make pulses as short as 100 picoseconds, with excellent control of the start time, and gives 10 or more times the beam intensity of conventional chopping. The technique uses pulsed voltages on both the Wehnelt grid and the anode of a typical electron gun, as shown in the drawing. The Wehnelt grid is pulsed for a few nanoseconds, to extract electrons, and the accelerating anode is pulsed for the duration desired. It is known that a pulsed Wehnelt grid produces a beam intensity about 10 times that of a DC biased grid, for a pulse of 3 to 5 ns [2]. However, it is not known if additional gains can be made for a shorter pulse. A short high voltage pulse is difficult to obtain by electronic means, but, as shown by LeFur and Auston [3], it is possible to switch
1.5 kilovolts on or off in less than 25 ps, by an optoelectronic switch governed by a laser. In the present technique a voltage equal to the cathode voltage is put on the anode several nanoseconds early, and is reduced to ground pot...