Stephan Schlamminger


LISA, Laser Interferometer Space Antenna, is, as indicated by its name, a space based gravitational wave detector. It is a joint effort by NASA and ESA and will be launched sometime in the near future.

Three satellites are at the corners of an equilateral triangle with a baseline of 5 million km. Inside each satellite, two proof masses define the ends of lines which join to form a vertex of the triangle. The proof masses are kept in free fall by servoing the satellites position around the proof masses without disturbing the proof masses trajectories.

An incident gravitational wave will change the distance between test masses on two different satellites. The interferometers formed by sending laser beams between spacecrafts will measure such a change in length.

Our research at the University of Washington focuses on possible unwanted interactions between the proof mass in one satellite and its housing. In particular, it has to be shown that disturbances due to fluctuating electric potentials are small enough such that the projected LISA sensitivity can be reached. We have built a very sensitive, i.e. low noise, torsion balance to measure such small fluctuations.

comparison of the LISA noise requirements and measured noise

The plot above shows the measured acceleration noise measured with the torsion balance converted into LISA units. The black line is the LISA requirement. The measured noise is about a factor of 10 above the LISA requirement. This is the limit of our instrument. In order to draw valid concusions for LISA we measure with ten times smaller gaps between proof mass and housing.

Presentation given at the 6th International Lisa symposium. (620 kB)