Numerical Simulations of Arm-locking for Taiji Space Gravitational Waves Detection

The laser frequency stabilization is one of the most important key technologies for the interferometer measurement system of space gravitational waves detection. As a proposed frequency stabilization technique, the scheme of arm-locking is to convert the stability of interferometer arm-length into the stability of laser frequency. Some numerical simulations of arm-locking for Taiji mission were investigated in the paper. Meanwhile, an innovative controller consisted of a compensation filter and two-stage integrators in parallel was presented to suppress the laser frequency noise without increasing gain and prevent the high gain from suppressing the gravitational waves signal. The single arm-locking simulation results showed that the laser noise of closed loop was lower than 3.19 mu m/root Hz@10 mHz only in the frequency range of 0.1 mHz - 0.03 Hz. But the dual arm-locking simulation results showed that the laser noise of closed loop was lower than 3.19 mu m/root Hz@10 mHz in the full frequency range of 0.1 mHz - 1 Hz, meeting the requirement of Taiji mission. Preliminary results represented the feasibility and effectiveness of arm-locking on laser frequency stabilization for the Taiji mission.