We present an interferometric technique for measuring ultrasmall tilts. The information of a tilt in one of the mirrors of a modified Sagnac interferometer is carried by the phase difference between the counter-propagating laser beams. Using a small misalignment of the interferometer, orthogonal to the plane of the tilt, a bimodal (or two-fringe) pattern is induced in the beam’s transverse power distribution. By tracking the mean of such a distribution, using a split detector, a sensitive measurement of the phase is performed. With 1.2 mW of continuous-wave laser power, the technique has a shot noise limited sensitivity of and a measured noise floor of for tilt frequencies above 2 Hz. A tilt of 200 frad corresponds to a differential displacement of 4.0 fm in our setup. The novelty of the protocol relies on signal amplification due to the misalignment and on good performance at low frequencies. A noise floor of about is observed between 2 and 100 mHz.
© 2017 Optical Society of AmericaFull Article | PDF Article
1 August 2017: A typographical correction was made to Ref. 6.
OSA Recommended Articles
Wei-Tao Liu, Julián Martínez-Rincón, Gerardo I. Viza, and John C. Howell
Opt. Lett. 42(5) 903-906 (2017)
Kunjian Cao, Yi Liu, and Shiliang Qu
Opt. Lett. 42(21) 4418-4421 (2017)
Xiao-Ye Xu, Wei-Wei Pan, Yaron Kedem, Qin-Qin Wang, Kai Sun, Jin-Shi Xu, Yong-Jian Han, Geng Chen, Chuan-Feng Li, and Guang-Can Guo
Opt. Lett. 45(7) 1715-1718 (2020)