LISA NASA engineering design unit (EDU) laser head metrology

The Laser Interferometer Space Antenna (LISA) mission will form an interferometer spanning arm lengths of 2.5 million kilometers to detect cosmic ripples in spacetime with a picometer resolution. To be able to measure gravitational waves, the laser system must meet stringent performance requirements including frequency noise, power stability, and sideband phase noise. A fully dedicated state-of-the-art measurement system has been developed by CSEM to properly characterize the performance of the NASA Laser Head (LH) against the system requirements. During extensive testing the laser head encountered a critical failure and by reviewing the telemetries, the NASA laser team found the root cause and provided an updated laser head with improved design for continued testing at CSEM. We present the frequency noise measurement system, combining the short-term stability of an optical reference cavity with the long-term stability of a maser with the help of an optical frequency comb used to measure the lasers frequency noise over 9 orders of magnitude. We also present the measurements obtained on the improved NASA LH of the amplitude noise and the side band phase noise and highlight the capabilities and the limitations of each measurement setup. Furthermore, the successful measurements of sideband phase noise performed with AEI collaboration are presented.