We demonstrate an experiment which utilizes a Sagnac interferometer to measure a change in optical frequency of 129 kHz per root Hz with only 2 mW of continuous wave, single mode input power. We describe the measurement of a weak value and show how even higher frequency sensitivities may be obtained over a bandwidth of several nanometers. This technique has many possible applications, such as precision relative frequency measurements and laser locking without the use of atomic lines.
@article{arxiv.1101.1464,
title = {Precision frequency measurements with interferometric weak values},
author = {David J. Starling and P. Ben Dixon and Andrew N. Jordan and John C. Howell},
journal= {arXiv preprint arXiv:1101.1464},
year = {2011}
}