Speaker
Description
Silicon nitride (SiN$_x$) is a highly versatile coating material. In high-reflection Bragg mirrors, it could be paired either with silica as high-index layer, for operation at any wavelength in the near infrared [1], or with amorphous silicon as low-index layer, for operation at a wavelength of 1550 nm or larger [2]; it could be used at ambient temperature as well as at cryogenic temperatures [3]. The LIGO and Virgo Collaborations have thus been studying SiN$_x$ thin films for more than a decade, using samples grown through a wide variety of deposition techniques.
Thanks to this extensive research work, the optical and mechanical properties of chemical-vapor deposited SiN$_x$ are now well known, both at ambient and cryogenic temperatures [3]. In contrast, despite ion-beam sputtering (IBS) being the reference deposition technique for coating the mirrors of gravitational-wave detectors [4], to the best of our knowledge the low-temperature loss angle of IBS SiN$_x$ has never been characterized so far.
In this talk we will present the results of cryogenic loss angle measurements of as-deposited and thermally-treated IBS SiN$_x$ thin films of the best optical quality achieved so far [1], and discuss them in light of their possible use in present and future detectors such as KAGRA and Einstein Telescope.
- [1] A. Amato et al., Phys. Rev. D 111, 042003 (2025).
- [2] J. Steinlechner et al., Phys. Rev. Lett. 120, 263602 (2018).
- [3] M. Granata, G2502437 / VIR-1117A-25 (2025).
- [4] M. Granata et al., Class. Quantum Grav. 37, 095004 (2020).