The Differential Optical Shadow Sensor (DOSS) is a sensor for measuring the position of a spherical test mass relative to a given reference system (housing). The major difference between the Shadow Sensor and an interferometric measurement is that the measurement for the Shadow Sensor is at the intensity level. That means, that there is no necessity for a coherent light source. The dynamic range of the shadow sensor is large as compared to an interferometric sensor.

Two light beams are tangent to the test mass such that the test mass partially blocks the beams. The difference between the intensity of the two beams is measured. This measurement principle is illustrated in the figure below for a one dimensional measurement with a single pair of detectors. The goal sensitivity is in the low nanometer range for frequencies of 1 mHz to 1 Hz.

DOSS Principle

The data acquisition and signal processing has the following features:

  • Compact low noise photodiode amplifier
  • 16-24 bit resolution
  • Lock-in amplification with DSP

The DOSS is currently developed as a CubeSat payload. A block diagram of the payload is shown below.

DOSS Block Diagram

Last modified Mon, 6 May, 2013 at 19:34