Low-frequency signals of large-scale gravitational-wave interferometers

The applicability of large-scale gravitational-wave interferometers for measuring low-frequency geophysical signals is considered. The main goal of this paper is to study the mechanism for the penetration of quasi-static geophysical perturbations to the high-frequency interferometer port. Attention is drawn to the parametric nature of this effect related to slow variations of the optical transfer function. The geophysical modulation index is calculated for all harmonics of the output spectrum and for the photon circulation frequency resulting from the noise illumination of neighboring optical modes near the central resonance. The model of an interferometer with a two-component pump is analyzed in an effort to improve the geophysical signal recording quality. Numerical estimates for various operating regimes of the instrument are presented, along with discussions of the possibility of recording weak gravitational effects.