Telescopes for LISA: function, current status, and path forward

The Laser Interferometer Space Antenna (LISA) will be a space-borne gravitational wave observatory that consists of three spacecraft, separated by several million kilometers, which tracks the separation between inertial test masses via laser interferometry. In this architecture strict requirements exist on the design of the orbits, the ability to accommodate laser frequency noise, the ability to provide the necessary purity of free-fall, and the quality of the optical metrology. This final item is enabled with afocal transmitting/receiving telescopes that increase the laser power transfer efficiency over the long inter-spacecraft link. These telescopes must be designed and built not to adversely affect the precision of the interferometric measurements. The function, design, and current status of LISA telescopes under development at NASA will be discussed in this article.