The compensation of the noise due to angular oscillations of the laser beam in the Precision Laser Inclinometer

An experimental method for the compensation of the noise originated by the laser ray angular oscillations was proposed and experimentally proved for the Precision Laser Inclinometer (PLI). The PLI noise spectral density was reduced by factor 30× and reached 10$^{–8}$ rad/Hz$^{1/2}$ level at the frequency of 5 × 10$^{–5}$ Hz. The angular noise of a laser ray leaving the one-mode optical fiber in the vacuum and in stabilized temperature conditions has been measured. The amplitude of the oscillations for one-day observation reached 0.46 μrad

The temperature stability of 0.005°C for the concrete floor in the CERN Transfer Tunnel #1 hosting the Precision Laser Inclinometer

To reach a sensitivity level of ~10$^{–9}$ rad for the Precision Laser Inclinometer (PLI) for the registration of the Earth surface angular oscillation in the low frequency band of [10$^{–6}$ Hz, 1 Hz] the temperature stability of the CERN Transfer Tunnel #1 has been investigated. The daily temperature variation was 0.082°C for the air and 0.005°C for the concrete floor. The last result opened the possibility to observe the Earth surface inclination caused by Moon and Sun if the PLI is thermally stabilized by the massive monolithic concrete floor of the tunnel

Determination of the maximum recording frequency by the Precision Laser Inclinometer of an earth surface angular oscillation

For the Precision Laser Inclinometer (FPI) using the I-20A oil, a high-frequency 4 Hz boundary was determined for reliable detection of the earth’s surface angular vibrations. The proposed method makes use of the microseismic signal and its processing to expand the PLI working interval for signal reception and allows to record the narrow frequency-band signals originated by the Earth surface angular oscillations caused by industrial sources