Optical displacement sensor (ODS): an inertial reference sensor candidate for LISA

Abstract

We propose here an optical displacement sensor (ODS) as a supplemental or backup sensor for the LISA inertial reference sensor concept. This simple ODS consists of a laser diode and a quad-cell photodiode (both commercially available). The inertial mass' reflective surface directs the laser beam onto the quad-cell photodiode. Changes in the inertial mass' position and orientation are then extracted from ratios of the differences and sums of the quad-cell photodiode outputs. A simpler proto-type using a 200 microns wide slit has demonstrated a resolution of 10 nm/square root Hz at 1 mHz and 1 nm/square root Hz above 5 mHz. The electronics noise was 1 nm/square root Hz at and above 1 mHz with simple and off the shelf electronics components. Although this ODS' current performance does not meet the LISA's system requirement1 of 1 nm/rtHz at 1 mHz, we think that is achievable in the near future.