Nanoradian angle measurements using differential Fabry-Perot interferometer

In this work, the novel angle measurement method that make use of Differential Fabry — Perot Interferometer (DFPI) and the High Precision Small Angle Generator (HPSAG) will be introduced. The DFPI using the frequency stabilized lasers and beat frequency measurement techniques was applied to the detection of ultra-small angles in the level of sub-nanoradian precision. During the application down to 1 nrad angular steps within the measurement range of 0.5 arcsec (2500 nrad) were generated using the HPSAG and these steps were detected by the DFPI which could measure angular displacements with picometer sensitivity free from linearity errors.