The detection of gravitational waves: the contribution of the Applied Physics Institute, Russian Academy of Sciences

Abstract

September 14, 2015 marked the day that the LIGO collaboration recorded a gravitational-wave signal arriving from the merger of two black holes that occurred 1.3 billion years ago. The LIGO detector is based on a Michelson interferometer with an arm length of 4 km. The achieved sensitivity makes it possible to detect a change of the arm length smaller than 10−19 meter. We discuss the physical problems that were solved in order to achieve this unprecedented sensitivity. The most essential contribution of the Applied Physics Institute, Russian Academy of Sciences, to the LIGO detector is the invention of unique Faraday isolators that operate with high laser radiation power. The absorption of radiation in a magneto-active medium unavoidably causes it to heat up and thermally induces polarization and phase distortion of the laser beam. This article presents an analysis of all the distortions of the laser beam from the viewpoint of the degradation of the parameters of the isolator. The mechanisms and key physical quantities responsible for the various forms of the distortions have been determined. The existing methods of compensating and suppressing parasitic thermal effects are described in detail.