High-precision, wide-range, dual-axis, angle monitoring system

A system is described that uses a helium–neon laser and lateral effect photodiodes to monitor the θ and φ angles of a test mirror. Accuracies of 0.01 arcsec are achieved short term in a laboratory environment. A bandwidth of 900 Hz allows simultaneous real-time angle monitoring on both coarse (10 000 arcsec) and fine (300 arcsec) angular ranges.