Abstract
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 56 frad/√Hz and a measured noise floor of 200 frad/√Hz 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 70 prad∕/√Hz is observed between 2 and 100 mHz.
| Original language | American English |
|---|---|
| Pages (from-to) | 2479-2482 |
| Number of pages | 4 |
| Journal | Optics Letters |
| Volume | 42 |
| Issue number | 13 |
| DOIs | |
| State | Published - 1 Jul 2017 |
| Externally published | Yes |
Bibliographical note
Funding Information:Army Research Laboratory (ARL) (W911NF-12-1-0263); Northrop Grumman, Department of Physics and Astronomy at the University of Rochester (UR); National Natural Science Foundation of China (NSFC) (11374368).
Publisher Copyright:
© 2017 Optical Society of America.