Characterization of integrating-sphere systematic effects for photon calibration of the KAGRA gravitational wave detector
Year: 2026
Type: preprint
Abstract: Photon calibration (Pcal) systems are essential for accurately reconstructing gravitational-wave strain in laser interferometric detectors. In the KAGRA Pcal system, the laser power applied to the end test mass is measured using integrating-sphere power sensors. During the first part of the fourth observing run (O4a), repeated calibration measurements showed scatter larger than expected from the uncertainties assigned to individual measurements. Although this excess scatter was empirically reflected in the previously reported calibration uncertainties, its physical origin was not identified. In this study, we experimentally characterize the response of the integrating spheres used in the KAGRA calibration chain with respect to three incident-beam conditions: incidence angle, polarization, and beam position. Based on these measurements and the reproducibility of the integrating-sphere placement in each calibration configuration, we evaluate the corresponding systematic uncertainties and explicitly incorporate them into the uncertainty model for the O4a Pcal-X calibration measurements. The inclusion of these previously unmodeled effects substantially improves the consistency between the estimated uncertainties and the observed scatter, particularly for calibration parameters measured at the KAGRA end station, where the reduced chi-square values decrease from values as large as $10^3$ to values of order unity to several. These results indicate that variations in the incident-beam conditions of integrating-sphere power sensors account for a substantial part of the previously unexplained scatter and establish a more physically motivated framework for evaluating Pcal laser-power calibration uncertainty. They also provide a basis for future reduction of the calibration uncertainty through improved control of the incident-beam conditions.
Source: arXiv (Cornell University)
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Foundation for Science and Technology Development, National Research Foundation, Ministry of Education, Culture, Sports, Science and Technology, Academia Sinica, Korea Institute of Science and Technology Information, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, Ministry of Science and ICT, South Korea, National Science and Technology Council, Japan Society for the Promotion of Science, Institute for Cosmic Ray Research, University of Tokyo, Great Southern Development Commission, Government of Western Australia
Awards: G1063769543, G12788915, G1907708792, G207645610, Pioneering High-Frequency Gravitational Wave Astronomy for Elucidating the Physics of High-Density Extreme Matter, G3774609052, G3984162807, G4480843407, Detection of gravitational waves with a cryogenic interferometer, G5793006848, Calibration Standard and High-Precision Data Analysis toward the Observational Era of Gravitational Waves, Thăm dò Vật chất tối bằng Sóng hấp dẫn và Từ trường Vũ trụ, G7259685644, G842060473, G8541542807, Inclusive study on gravitational-wave astrophysics
OpenAlex ID: W7223060407