Microfocus x-ray tube with optical spot size sensing means

Abstract

A microfocus X-ray tube has an anode that emits X-rays and, a biproduct of its waste heat, visible and near infrared light. This invention uses the biproduct light to adjust and maintain the focus of the electron beam and enhance the performance of the X-ray tube as a point source of X-rays. Only the light is reflected by a mirror along a path in which a viewport is placed in the tube envelope. An sensor, e.g., a photodiode, or television camera, is placed in the path. A display means, e.g., a television display, meter, etc., can be connected to the sensing means to display the emitting spot of the anode or the amplitude of the emission. The focus of the X-ray tube is assured by observing the biproduct light and adjusting the electron beam to either minimize the size of the glowing spot or maximizing its apparent brightness. A method for use with an emitter of first and second types of radiation comprises reflecting only the second type of radiation, and sensing the reflected radiation. A microfocus X-ray tube features a mirror for reflecting light but not X-rays. A viewport such as quartz can be disposed in the path of the reflected light in the tube envelope.