Ultra-low-noise laser intensity noise evaluation system in Hz frequency band for ground-based gravitational wave detection
Authors: LI Xiang , WANG Jiawei , LI Fan , HUANG Tianshi , DANG Hao , ZHAO Desheng , TIAN Long , SHI Shaoping , LI Wei , YIN Wangbao , ZHENG Yaohui ,   State Key Laboratory of Quantum Optics Technologies and Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   State Key Laboratory of Quantum Optics Technologies and Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2024

The direct detection of gravitational waves has opened up a new window for understanding the universe and trailblazed multi-messenger astronomy. The frequency bands of gravitational waves generated by various astronomical events can cover a broadband range, and the detection mechanisms and schemes for gravitational waves in different frequency bands are different. For example, the ground-based gravitational wave detection has a frequency band ranging from 10 Hz to 10 kHz, which is based on Michelson interferometer. The space gravitational wave detection has a frequency band in a range of 0.1 mHz–1 Hz , which is based on space interferometer. The pulsar gravitational wave detection has a frequency band ranging from 1×10<sup>–9</sup> Hz to 1×10<sup>–7</sup> Hz, which is based on pulsar timing array. The next-generation ground-based gravitational wave project requires higher sensitivity to detect faint signals, necessitating an assessment system with minimal background noise to accurately measure the laser relative intensity noise. At present, the detection frequency band of ground-based gravitational wave detection devices in operation is mainly concentrated in a range of 10 Hz–10 kHz. To satisfy the detection sensitivity requirements, the laser relative intensity noise should be accurately evaluated and suppressed to ≤2.0×10<sup>–9</sup> Hz<sup>–1/2</sup> at 10 Hz and ≤4.0×10<sup>–7</sup> Hz<sup>–1/2</sup> at 10 kHz by photoelectric feedback. In this work, an evaluation and characterization system is constructed for ground-based gravitational wave band laser intensity noise, which is based on low noise and high sensitivity photoelectric detection device and combined with LabVIEW and MATLAB algorithm programming for instrument control and data processing. This low noise evaluation system is used to test the background noise of fast Fourier transform (FFT) analyzer SR760, preamplifier SR560, photoelectric detector electronic noise and intensity noise of homemade optical fiber amplifier, and then the data extraction and image processing are carried out by LabVIEW and MATLAB algorithms, and finally the ground-based gravitational wave frequency band system is evaluated. The experimental results show that the electronic noises for the preamplifier SR560 and the FFT analyzer SR760 are lower than 3.8×10<sup>–9</sup> Hz<sup>–1/2</sup>@(10 Hz–10 kHz). The electronic noise for the photodetector is lower than <inline-formula><tex-math id="M3">\begin{document}$ 1.4 \times {10^{ - 8}}\;{\text{V}}/\sqrt {{\text{Hz}}} $\end{document}</tex-math></inline-formula> at 10 Hz and <inline-formula><tex-math id="M4">\begin{document}$ 8.1 \times {10^{ - 9}}\;{\text{V}}/\sqrt {{\text{Hz}}} $\end{document}</tex-math></inline-formula> at 10 kHz, and the accuracy of the system is calibrated and tested by the standard sinusoidal signal. Finally, the noise of commercial laser is evaluated and compared with the factory data to verify the accuracy of the evaluation system. Related research, device and system development provide hardware, software and theoretical basis for preparing high-power low-noise laser light source and gravitational wave detection, and also provide the theoretical basis and evaluation criteria for detecting the ground-based gravitational wave .