The Compact Nanoradian Precision Laser Inclinometer—an Innovative Instrument for the Angular Microseismic Isolation of the Interferometric Gravitational Antennas

The conceptual new design of the Precision Laser Inclinometer (PLI) is proposed and developed what resulted in creation of compact instrument for its possible use in a restricted vacuum volume of sensitive elements of Gravitational Wave Interferometric Antennas. It is shown that the use of a position sensitive method—the dividing plates method—for the detection of angular inclination of laser beams, allows to reduce the dimensions of the PLI to a cube of 11 × 11 × 15 cm$^{3}$ or to a cylinder with a diameter of 15 cm and a height of 11 cm. The reduction of the dimensions results in a simultaneous increase of 1.9 times in the sensitivity of recording the angular inclinations of the earth’s surface.