2025/10/29 by Wissel, L., Hewitson, M., Heinzel, G.
#530 #Differential wavefront sensing #Direct measurement #Heterodyne detection #Heterodyne interferometer #Heterodyning #Interference phasis #Interferometers #LISA Pathfinder #Laser intensity fluctuations #Laser interferometry #Measurements of #Phase noise #Phase-noise #Relative intensity noise #Space missions #Wavefronts
paper · doi:10.15488/19914
Laser-intensity fluctuations cause undesired phase noise even in balanced heterodyne interferometers. However, in space missions in particular, such as LISA Pathfinder or LISA, direct measurements of these fluctuations at the relevant frequencies are often not available. Hence, it can be challenging to estimate their impact on the interference phase. To address this, we propose a new method for characterizing laser relative intensity noise (RIN) using differential wavefront sensing (DWS), with the latter being a well-established technique typically used for angular sensing and control. Unlike other methods, this approach does not require an additional reference interferometer and instead takes advantage of the inherent phase subtraction of DWS. This allows us to estimate the RIN value at the heterodyne frequency and its harmonic, relative to the sensor noise floor of the total measurement system. Moreover, it provides a strategy to identify the ideal set point for minimizing RIN couplings in DWS.