High-Precision Small-Angle Measurement of Laser-Fiber Autocollimation Using Common-Path Polarized Light Difference

The laser autocollimation measurement method is an important technique for the precise measurement of small angles. However, the beam drift significantly affects the accuracy and stability of laser autocollimation. This article is the first to present a laser-fiber autocollimation method for measuring small angles with the difference in common-path polarized light. In principle, this method greatly reduces the laser beam drift caused by various factors and significantly improves the measurement accuracy and stability. The effects of the factors affecting beam drift on small-angle measurement were analyzed and simulated. A corresponding measurement system was developed with the capability to measure not only small angular changes in a single object but also relatively small angular changes between two objects, and a series of experiments were conducted. The results indicated that the angle measurement stability was improved by 90%–98% using the difference in common-path polarized light to compensate the beam drift caused by mechanical structure drift, vibration, and environmental disturbance. Extremely high measurement stability of 0.07 in 10 h and
$0.04''$
in 2 h was obtained at 500 mm. Furthermore, the measurement system was effectively used to measure the thermal stability of a star sensor bracket of a satellite, yielding a thermal stability of
$0.15''/^{\circ }\text{C}$
to meet the on-orbit operational stability requirement of
$0.25''/^{\circ }\text{C}$
. Thus, this new method compensates for beam drift in the autocollimation measurement of small-angle changes in a single object and relatively small angular changes between two objects.