Research on low noise balanced homodyne detection system for space-based gravitational wave detection (Invited)

The space-based gravitational wave detection frequency band is located in the range of 0.1 mHz-1 Hz, because the gravitational wave source information with larger characteristic quality and scale is contained in the aforementioned frequency band. At present, large-scale laser interferometer space-based gravitational wave detection projects based on different sizes and space orbits have been gradually implemented. It should be emphasized that the laser intensity noise and frequency noise should be suppressed in the laser source system of the interferometer. Moreover, as the first level device of laser noise characterization and suppression, the performance of photoelectric detection will directly affect the effect of laser noise suppression. First of all, on the basis of selecting low noise chip and high stable bias system, the whole circuit was designed by self-reducing circuit and transimpedance-amplifying circuit. In addition, in electromagnetic shielding, low temperature drift factor element, low noise power supply and active temperature control and other technical means, realize the development of high gain and low noise balanced homodyne detection system. Finally, the gain and bandwidth of the photodetector were evaluated and tested by combining the fast Fourier transform method and the number line power spectral density algorithm, and the intensity noise of the laser was detected and characterized in the 0.05 mHz-1 Hz band by using the detector. The experimental results show that the electronic noise spectral density of the balanced homodyne detector is less than 3.6×10⁻⁵ V/ Hz^1/2 in the frequency range of 1 mHz-1 Hz, which is less than the noise requirement of the laser source for space-based gravitational wave detection. When the incident light power is 400 μW, the gain of the balanced homodyne detection system is measured to be more than 40 dB in the frequency range of 0.1 mHz-1 Hz. What’s more, the spectral density of laser intensity noise is 3.6×10⁻² V/ Hz^1/2 at 1 mHz. Low noise photoelectric detection and laser intensity noise characterization are achieved, which provide key device support for laser intensity noise characterization and suppression in space-based gravitational wave detection.