Design and development of an interferometric readout for planetary seismometers.
Résumé
Seismometers are now likely to be placed on other planets and a seismic return on the Moon is currently considered. Indeed, the Apollo seismometers had a good sensitivity : 60 pm/√Hz at 1 Hz but were however unable to detect all the seismic signals produced by the Moon, like the 'lunar continuous meteoritic hum'. The different core seismic phases, although detected through stacking, have not also been individually recorded. A new generation of broadband planetary seismometers, 100 to 1000 times more sensitive than the Apollo ones is thus required. The idea consists in using the gravitational waves detectors' technology which are the reference in terms of interferometric measurements at low frequency and very low noise levels in order to improve the performances (linearity and noise level) of the seismometers' mass displacement sensors. The final objective is to reach a sensitivity of 40 fm//√Hz at 1 Hz. An optical readout is proposed, based on the Pound-Drever Hall laser frequency stabilization method, and the preliminary theoretical and experimental results show a sensitivity of 12.8 fm/√Hz at 1 Hz in the worst case by only considering the optical and mechanical parts.