Coupling of TTL noise in the TDI data stream—a preliminary study based on EPD

Abstract Significant suppression of laser frequency noise is required for space-based gravitational wave detectors operating within the 0.1 mHz to 1 Hz range, where residual sensitivity can be limited by secondary effects such as tilt-to-length (TTL) coupling noise. In this work, realistic laser frequency noise and TTL coupling noise are modeled and injected at the interferometric phase measurement level in a semi-physical experiment based on an electronic phase delay (EPD) test bench. Using the Michelson-X time-delay interferometry (TDI) configuration, laser frequency noise is effectively suppressed, whereas TTL coupling noise remains as a residual contribution after TDI processing. The residual TTL coupling noise is experimentally quantified and its spectral behavior is analyzed, demonstrating the propagation of TTL-induced phase fluctuations into the TDI data stream. These results provide experimental constraints on TTL effects in TDI-based space gravitational wave detectors.