Spaceborne Laser Transmitter Development for the Laser Interferometer Space Antenna (LISA) Mission

The Laser Interferometer Space Antenna (LISA) is a partnership between the European Space Agency (ESA) and NASA to build a Gravitational Wave (GW) observatory. The observatory, which consists of a three-spacecraft constellation with a nominal separation of 2.5 million km between each spacecraft, provides a tool for scientists to directly detect gravitational waves generated from various astronomical phenomena in a waveband that is not accessible from Earth. NASA is developing laser transmitters as one of the potential US contributions to LISA. The NASA laser design leverages lessons learned from previous flight missions, and includes the latest technologies in photonics packaging and reliability engineering to ensure a laser lifetime of 16 years covering integration and test through a possible extended mission phase.

The laser system is one of the most important components of the LISA measurement system, since it will provide the light used to make the sensitive interferometric distance measurement between the spacecraft. We at the NASA GSFC have been developing a highly stable and robust master oscillator power amplifier (MOPA) laser system for LISA since 2018. The MOPA architecture entails two major subsystems – (i) the master oscillator (MO), a lower power laser that meets majority of the laser requirements except power; and (ii) the power amplifier (PA), which boosts the low output power of the MO to the required power without imparting additional noise. Our laser design philosophy is driven by LISA’s unique requirements arising from its role in the extremely long-baseline interferometric measurement system. It must have exquisite stability in both wavelength (which requires active stabilization using a high finesse optical cavity) and intensity (which requires active stabilization for long-term drifts and quantum-limited performance over short time scales). In addition the laser must be robust enough to survive the 16 years of operation from early ground testing through the extended mission phase.

The unique LISA requirements make evaluation of the laser performance challenging. To enable testing of these lasers, we built a unique laser characterization infrastructure that does not exist in industry, other Government labs, or academia. These in situ test capabilities provide important advantages including: time savings, cost savings, and improved ability to meet compliance requirements.

In this talk we will discuss the NASA GSFC laser development effort for LISA with emphasis on: (1) the design and packaging of the MOPA laser, (2) reliability and risk mitigation plan to show compliance with the 16-year LISA lifetime requirement, and (3) test facilities for the demonstration of laser performance. We are targeting a delivery of a form, fit, and functional laser to ESA in 2020 and a fully space-qualified TRL6 MOPA laser by mid-2021.

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