Design, fabrication, and verification of a three-dimensional autocollimator

The autocollimator is an optical instrument for noncontact angle measurement with high resolution and a long detection range. It measures two-dimensional angles, i.e., pitch and yaw, but not roll. In this paper, we present a novelly structured autocollimator capable of measuring three-dimensional (3D) angles simultaneously. In this setup, two collimated beams of different wavelengths are projected onto a right-angle prism. One beam is reflected by the hypotenuse of the prism and received by an autocollimation unit for detecting pitch and yaw. The other is reflected by the two legs of the right-angle prism and received by a moiré fringe imaging unit for detecting roll. Furthermore, a prototype is designed and fabricated. Experiments are carried out to evaluate its basic performance. Calibration results show that this prototype has angular RMS errors of less than 5 arcsec in all 3Ds over a range of 1000 arcsec at a working distance of 2 m.