Accurate Measurement of Gravitational Waves with the Photon Calibrator
Yuki Inoue1,2*, Tomotada Akutsu3, Sadakazu Haino1, Nobuyuki Kanda4, Yuta Michimura5, Keiko Kokeyama6, Takahiro Miyamoto6, Richard Savage7, Toshikazu Suzuki2, Takayuki Tomaru2, Takafumi Ushiba5, Takahiro Yamamoto6, Takaaki Yokozawa4
1Institute of Physics, Academia Sinica, Nankang,Taipei, Japan
2High energy research organization, Tsukuba, Ibaraki, Japan
3NAOJ, Mitaka,Tokyo, Japan
4Graduate school of science, Osaka city university, Osaka,Osaka, Japan
5Institute of Physics, The university of Tokyo, Bunkyo, Tokyo, Japan
6ICRR, Kashiwa,Chiba, Japan
7LIGO Hanford Observatory, Hanford,WA, USA
* presenting author:Yuki Inoue,
One of the most exciting discoveries of this century is the direct direction of the gravitational waves (GWs) with the Advanced LIGO experiment. GWs are one of the most promising predictions from the general relativity, which is beyond the Newtonian mechanics established by Einstein 100 years ago. However, the predicted distortion of space-time is much small. GWs induce strain on the order of 10-²⁰/√Hz. The typical interferometer arm is on the order of kilometers, thus producing a necessary testmass displacement sensitivity of around 10-¹⁷m/√Hz. Thus, we require the high-sensitive observation technology. Scientists have spent 100 years on achievement of detection for GWs until now.
Worldwide observation network of GW experiments is essential for accurate measurement of GW properties. Following Advanced LIGO, KAGRA and Advanced VIRGO plan to start the operation in coming years. The goal of KAGRA, Advanced LIGO, and Advanced VIRGO is to directly explore new physics with GWs. Advanced LIGO, KAGRA, and Advanced VIRGO can detect the GWs from astronomical sources using Michelson interferometer with a Fabry-Perot cavity with a length of several kilometers in both arms. The arm lengths of the interferometer correspond to the frequency of the observation. The targets of the frequencies of a ground- based interferometer are between 1 Hz and 4000 Hz.
In order to pursue the new physics with the world observation network, we need to calibrate the absolute amplitude and phase of the waveform by each GW detector. The previous study has shown that optimizing scientific benefit requires calibration accuracies on the order of 10 % for the first detection of GW. However, we require 0.5 % uncertainty for later measurement.
The KAGRA group plan to employ the photon calibrator so-call “Pcal”. The Pcal is already used by Advanced LIGO. The Pcal uses power-modulated auxiliary lasers to induce periodic modulation in the position of a suspended mirror via photon radiation pressure. The force is associated with displacement proportional to both the force and the power of laser. KAGRA and Advanced LIGO plan to improve Pcal, whose goal of uncertainty is less than 0.5 %.
In this talk, we will be talking about the plan and progress KAGRA Pcal studies.

Keywords: KAGRA, Gravitational Waves, Calibrator, Photon pressure