Compact quasi-monolithic heterodyne laser interferometer

Compact quasi-monolithic heterodyne laser interferometer Yanqi Zhang,Hayden Wisniewski,Andrea Nelson,Ki-nam Joo,Felipe Guzman Heterodyne laser interferometry has demonstrated the required sensitivities for reading out displacement of free-falling test masses in space-based gravitational wave observatories. We are currently developing a compact heterodyne laser interferometer that can be fabricated and integrated in a single quasi-monolithic block. In this design, the spatially separated heterodyne sources eliminate the effects of periodic errors. The highly common optical paths between the measurement and reference interferometers, and the equal nominal optical pathlengths between two arms in each interferometer provide a high common-mode rejection ratio to typical noise sources. In addition, a periodic-error-free heterodyne interferometer operated at 632.8 nm has been built and tested in the lab as a benchtop prototype. This interferometer is able to achieve picometer-level displacement sensitivities in air over frequencies above 100 mHz. A quasi-monolithic and highly compact version of this interferometer operating at 1064 nm, is currently under development. We will present our designs and current results on both systems.