A simple high-sensitivity interferometric position sensor for test mass control on an advanced LIGO interferometer

A small Michelson interferometer has been configured as a tracking mirror d isplacement sensor in order to achieve both large dynamic range (2.1 mm) an d excellent sensitivity (2 x 10(-14) m/root Hz) across a broad frequency ra nge (6Hz-3 kHz). The interferometer is illuminated by a simple LED, uses br oadband, non-polarising beamsplitters and contains no lensing optics. A DC- coupled balanced detector provides an error signal that is used to position the tracking mirror of the Michelson interferometer so as to maintain an i nterferometer operating position close to the centre of a particular fringe . The total interferometric sensor provides a small, simple and cost-effect ive means of achieving high-resolution displacement measurements.