Tilt-to-length coupling calibration in the LISA mission: uncertainty and biases

The Laser Interferometer Space Antenna (LISA) will be the first gravitational wave detector in space. It requires a picometer precision in the mHz regime, making stringent noise handling necessary. After the suppression of laser frequency noise in post-processing, one of its most significant noises will be the coupling of angular jitter into the interferometric measurements. This is called tilt-to-length (TTL) coupling.

In flight, the TTL noise will be suppressed by subtraction in post-processing. This method utilizes angular interferometric readouts. Its success depends on the accuracy of the TTL coupling calibration and distinction from other noise sources and gravitational wave signals.

In our latest analyses, we could show that this accuracy varies significantly for different estimators if the levels of angular jitter or readout noise are altered. Provided prior knowledge of the readout noise, the bias of the estimators can be computed and corrected analytically. These results make us confident that the TTL coupling noise can be successfully calibrated even if the readout noises exceed their requirements.