Characterization of integrating-sphere systematic effects for photon calibration of the KAGRA gravitational wave detector
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 103 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.
Related
- Detectability-Aware Screening of Post-Merger Gravitational-Wave Damping Anomalies in Real Detector Noise: A Graph-Spectral Approach with Empirical Null Calibration
- Unified matched-filter and excess-power pipeline for gravitational-wave detector characterization
- Detector orientation matters: Consequences for gravitational-wave background detectability
- Accounting for detector calibration uncertainty in black-hole ringdown analysis
- Polarized Anisotropic Stochastic Gravitational Wave Background Search with Ground-Based Detector Networks
BibTeX
@misc{hido2026characterization,
title = {{Characterization of integrating-sphere systematic effects for photon calibration of the KAGRA gravitational wave detector}},
author = {Shingo Hido and Misato Onishi and Shinji Miyoki and Takahiro Sawada and Takahiro Yamamoto and Takayuki Tomaru and Yoshiki Moriwaki and Dan Chen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25581},
eprint = {2610.25581},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25581},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Characterization of integrating-sphere systematic effects for photon calibration of the KAGRA gravitational wave detector
AU - Shingo Hido
AU - Misato Onishi
AU - Shinji Miyoki
AU - Takahiro Sawada
AU - Takahiro Yamamoto
AU - Takayuki Tomaru
AU - Yoshiki Moriwaki
AU - Dan Chen
PY - 2026
DA - 2026/10/18
PB - arXiv
DO - 10.48550/arxiv.2610.25581
UR - https://arxiv.org/abs/2610.25581
AB - 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.
ER -