Transponder-type laser interferometer prototype for spaceborne gravitational wave detectors

Transponder-type laser interferometry is essential in spaceborne gravitational wave detection missions. This paper presents a transponder-type laser interferometer prototype for potential noise calibration of spaceborne gravitational wave detectors. Using a digital optical phase-locked loop, we successfully locked the phase of the slave laser to the master laser (similar to 200 pW). Once the link between the master laser and the slave laser is established, the two satellites (essentially two lasers) form a transponder-type laser interferometer. We carefully analyze the measurement stability and noise characteristics of the interferometer, and the results show that the Allan deviation of the zero drift can reach 243.2 pm at t = 0.429 s, while the noise spectral density has a typical 1/ f line shape with a floor of 21 pm/Hz1/2 at 1 Hz. The coherence analysis shows that the temperature drift is an important factor limiting the performance of the interferometer below 2 mHz, while the frequency noise of the master laser is not dominant in the experiment. Transponder-type laser interferometers have a wide range of applications in intersatellite communication and measurement. Our design can serve as a valuable reference for gravitational wave detection missions such as LISA. (c) 2024 Optica Publishing Group