A construction method of the quasi-monolithic compact interferometer based on UV-adhesives bonding

Abstract: Quasi-monolithic interferometers play a crucial role in high-precision measurement experiments, including gravitational wave detection, inertial sensing, vibrometry, and seismology. Achieving high stability and accuracy in such interferometers requires a method for bonding optical components to a baseplate. While optical contact bonding and silicate bonding are common methods, UV adhesives offer advantages such as controlled curing and low geometrical requirements for optical components and baseplates. This paper presents a detailed construction method for a quasi-monolithic compact interferometer based on UV-adhesive bonding. We built two types of interferometers using this method: a $100\,{\rm mm} \times 100\,{\rm mm}\times 20\,{\rm mm}$ Mach-Zender homodyne interferometer with unequal arm lengths of about $100\,{\rm mm}$ for laser frequency noise monitoring, and a heterodyne interferometer as a displacement sensing head sizing $20\,{\rm mm} \times 30\,{\rm mm}\times 20\,{\rm mm}$. Our Mach-Zender interferometer achieved a phase noise level of $2\,\mu{\rm rad}\sqrt{{\rm Hz}}$ at $1\,{\rm Hz}$ and a equivalent laser frequency noise monitoring sensitivity of about $1\,{\rm kHz}/\sqrt{{\rm Hz}}$ at $1\,{\rm Hz}$. The compact heterodyne interferometer sensing head showed a sensitivity level of $1\,{\rm pm}/\sqrt{{\rm Hz}}$ in translation and $0.2\,{\rm nrad}/\sqrt{{\rm Hz}}$ in two tilts above $0.4\,{\rm Hz}$. Our tests demonstrate that quasi-monolithic compact interferometers based on UV-adhesive bonding can achieve high sensitivity levels at the pico-meter and nano-radian scales.