Common-path design criteria for laser datum based measurement of small angle deviations and laser autocollimation method in compliance with the criteria with high accuracy and stability.

Common-path design criteria for laser datum based measurement of small angle deviations are proposed to guide the implementation of common-path principle in dealing with laser beam drifts resulting from laser generation mechanism and instability of beam transmission medium. A laser autocollimation method is designed in compliance with the criteria, and can achieve an accuracy of 0.013 arcsec and a two-hour stability of 0.020 arcsec over a measurement distance of two meters. The criteria and the method proposed can be effectively used for laser datum based measurement of small angle deviations with high accuracy and stability, especially over a long measurement distance.