Overview of KAGRA: Calibration, detector characterization, physical environmental monitors, and the geophysics interferometer

Abstract

KAGRA is a newly built gravitational wave observatory, a laser interferometer with a 3 km arm length, located in Kamioka, Gifu, Japan. In this series of articles, we present an overview of the baseline KAGRA, for which we finished installing the designed configuration in 2019. This article describes the method of calibration (CAL) used for reconstructing gravitational wave signals from the detector outputs, as well as the characterization of the detector (DET). We also review the physical environmental monitors (PEM) system and the geophysics interferometer (GIF). Both are used for characterizing and evaluating the data quality of the gravitational wave channel. They play important roles in utilizing the detector output for gravitational wave searches. These characterization investigations will be even more important in the near future, once gravitational wave detection has been achieved, and in using KAGRA in the gravitational wave astronomy era.

Optimal Design of Coatings for Mirrors of Gravitational Wave Detectors: Analytic Turbo Solution via Herpin Equivalent Layers

“…To reduce this source of noise, researchers can act by using different materials with the best properties for the mirrors, optimizing the interferometer's laser beam, lowering the temperature to cryogenic values, and finally acting on the coating design. Unfortunately, there are not many glassy materials that satisfy the optical requirements necessary for gravitational wave detectors, the improvement of the laser beam would require a rethinking of the whole interferometer cavity as well as make this cavity cryogenic (see the papers [3][4][5] for a review on the subject).…”

Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)

“…The main optics of the interferometer are initially aligned before the lock acquisition procedure, as follows. Each arm cavity is independently aligned such that the high-visibility flashes of green light are observed by the PD at each transmission port and the CCD camera looking at each end mirror surface [14], whereas all the other mirrors are misaligned. After recording the optimal angles of ETMX, ITMX, ETMY, and ITMY mirrors, the short Michelson interferometer (composed of the BS, ITMX, and ITMY mirrors) is configured, and the BS is aligned to attain the high visibility of the Michelson interferometer.…”

“…The details of the O3GK calibration are described in Refs. [14,39]. The calibrated data used in this study are derived in a real-time digital control system with infinite impulse response filters that simulate the pre-measured optical response and actuator functions with an error of approximately 15% in magnitude.…”

Detector Characterization and Mitigation of Noise in Ground-Based Gravitational-Wave Interferometers

“…Figure 1 illustrates the central role of characterizing the detector and its data quality to the flow of LIGO data analysis from the instruments to the final output of gravitational-wave catalogs. As gravitational-wave astronomy grows, detector characterization and noise mitigation continue to play an important role in the maximization of detector sensitivity and analysis precision [15,18,19].…”