Design and Evaluation of Cosmic Explorer Layouts

Cosmic Explorer (CE), the next-generation US gravitational-wave (GW) observatory, aims to push the boundaries of sensitivity and detection range beyond aLIGO by employing larger interferometers and advanced optical systems. One of the key challenges in its design is optimizing the interferometer layout to achieve superior performance while ensuring compatibility with various subsystems. This analysis explores alternative interferometer configurations for CE, analyzing their benefits and limitations, and recommending two promising designs for further optical development.

The “Long Reverse aLIGO” layout is a modified version of the existing aLIGO that reduces beam size at the beam splitter (BS) by positioning telescopes between the BS and the 40km arm cavities. Moreover, two additional optics are added in the power recycling cavity (PRC), enabling independent mode matching for both the PRC and signal extraction cavity (SEC) to the common arm mode of the interferometer.

The 'Long Crab' layout uses curved folding mirrors to steer the beams from the arms, achieving an angle of incidence significantly less than the traditional 45 deg used in current GW detectors. Thermal modeling of the BS has indicated that low angle of incidence may be necessary for achieving the required detector performance at high circulating light powers. This innovative design lays a strong foundation for improving the CE, enhancing its sensitivity and ensuring optimal performance for the next generation of GW detection.