A micro-angle sensor based on laser autocollimation

This paper describes a micro-angle sensor based on laser autocollimation. The sensor consists of a light source, an objective lens and a positioning-sensing device. The position-sensing photodetector, which is a quadrant photodiode, is placed at the focal position of the objective lens. Differing from a conventional autocollimator, the angle sensor employs a laser diode as the light source. The laser beam is collimated to a thin parallel beam with a diameter of 1 mm so that the angle sensor can be used to detect the surface local slope of a specimen. The thin laser beam also makes it possible to use a small target mirror for measurement of stage angular error motions. Because the sensitivity of angle detection does not depend on the focal length of the objective lens by using a laser source, an objective lens with a short focal length is employed for realizing a compact sensor size. The prototype micro-angle sensor has a dimension of 26mm × 22mm × 12 mm. The resolution is better than 0.1 arc-seconds. Optical design and experimental results of confirming the performance of the sensor are presented.