| 摘要 |
PURPOSE:To accurately obtain a spot irradiation position in a short time with simple constitution by forming images of photoelectrons emitted by a photoelectric film through an electron lens and multiplying the electron images by a microchannel plate (MCP). CONSTITUTION:When the photoelectric film 11 is irradiated with spot light, photoelectrons are emitted on the reverse surface of the film 11. Photoelectrons are accelerated by the electron lens 12 to form electron images on the front-side surface of the MCP13. The photoelectrons are multiplied when passing through thin holes constituting the MCP13 and strike on a resistance body 14 when emitted from the reverse surface, so that currents begin to flow out of electrons 15 and 16. Resistances ra and rb are present between the electrodes 15 and 16 and the currents Ia and Ib flowing of the electrodes 15 and 16 are so determined as to be Ia/Ib=la/lb, where la and lb are the distances between a point SP and the electrodes. For the purpose, the ratio of currents flowing from terminals 17 and 18 to a signal processor 19 is computed to easily know the position of the SP as a value lb.
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