Large scale laser gravitational interferometer with suspended mirrors for fundamental geodynamics

摘要

A Fabry-Perot-Michelson gravitational free mass interferometer is considered for a registration of the low frequency-Earth gravity gradients. A variation of the Earth gravity force vector cause the corresponding misalignment of the interferometer mirrors thus providing information about the Earth gravity field. Gravitational interferometer with suspended mirrors provides a unique possibility to measure a relative angle variations between two "plumb lines" (gravity force vectors) separated by the large distance 3 / 4 km. So at very low frequencies the set up presents a long based angular gravity gradiometer for registering global geodynamics through the surface gravity gradient. A possibility of measuring the geophysical phenomena resulted in gravity field variations (core movements, Earth free oscillations, tidal harmonics, Earth rotation variations, etc.) is discussed and technical requirements for the set up optical elements are formulated. Comparison with conventional geophysical devices is carried out. Estimates of the basic instrumental and seismic noises limiting the sensitivity at low frequency (in the quasi-static regime) are discussed briefly. These estimates show that there is a hope for measurement of the gravitational angular perturbation of the mirrors at the level of 10~(-12)/10~(-13) rad for the observation time about several hours. The possibility of arm signals reconstruction in the presence of recycling mirror is demonstrated. The auxilliary optical system for precise justification between up-down movements and tilts of the end spherical mirrors is considered. The requirements on the stability of laser system are discussed.