Integrated Differential Optical Shadow Sensor for Modular Gravitational Reference Sensor

The Laser Interferometer Space Antenna (LISA) is a proposed space mission for the detection of gravitational waves. It consists of three drag-free satellites flying in a triangular constellation. A gravitational reference sensor is used in conjunction with a laser interferometer to measure the distance between test masses inside the three satellites. Other future space mission such as DECIGO and BBO also require a gravitational reference sensor. The Modular Gravitational Reference Sensor (MGRS) is being designed for these purposes and consists of two different optical sensors and a UV LED charge management system. The Differential Optical Shadow Sensor (DOSS) is one of the optical sensors and measures the position of a spherical test mass with respect to the surrounding satellite. This measurement is used for the drag-free feedback control loop. This paper describes the most recent, third generation of the experimental setup for the DOSS that uses a fiber coupled super luminescent LED, an integrated mounting structure and lock-in amplification. The achieved sensitivity is 10 nm/Hz^(1/2) above 300 mHz, and 20 nm/Hz^(1/2) for frequencies above 30 mHz.