Performance Testing of TRL4-6 LISA Laser System

The Laser Interferometer Space Antenna (LISA) is an ESA-led future mission to measure gravitational waves from astronomical sources in space. LISA has been adopted as a formal mission by ESA in January 2024, and is expected to become a formal project at NASA within 2024. The laser system (LS), which includes four laser heads (LH) each containing a laser optical module (LOM) and laser electronics module (LEM), a frequency reference system (FRS, optical frequency reference) and four power monitor detectors (PMON), is one of the three U.S. contributions to LISA from NASA. The Lasers and Electro-Optics Branch at NASA GSFC has been developing and managing the design of the LISA LS. Currently, the TRL (technology readiness level) of the NASA LISA laser system is transitioning from 4 to 6. TRL 4/5 LISA LOM was sent to ESA in early 2023 and has undergone optical performance testing. [1] By late summer of 2024, NASA plans to deliver the TRL 6 LOM to ESA for performance evaluation.

Since the delivery of the TRL4/5 LOM to ESA, we have taken steps to advance the TRL of the overall LS and have also started end-to-end system level testing involving other subsystems. They include 1) optical performance test of TRL6 LOM and TRL 5 LEM under thermal cycling, 2) end-to-end test of the laser head (LH) and the GSE (ground support equipment) FRS, driven by TRL 4 FRS electronics (FRS-E) provided by Ball Aerospace, 3) end-to-end test of the laser head (LH) with the GSE phase meter system (PMS) provided by Albert Einstein Institute, and 4) optical performance test of the LH with the PMON subsystem developed by NASA. The FRS, PMS, and PMON provide necessary frequency stability, relative phase stability between lasers, and output power stability, respectively. Since they are all vital for the sensitive laser interferometry performed in LISA, it is necessary to perform these system level testing by combining the LH and other subsystems, and to prove the optical performance at an early stage during the LS development.

Our recent work has successfully demonstrated the intra-connectivity of the LS, as well as critical external interface with the PMS to meet the LISA’s performance requirements. In this talk, we will report on the latest status of the LH testing and system level test. We will also discuss the paths to bring each subsystem to TRL6+ and plans for future system level testing.