Hybrid metasurface-Bragg mirror cuts coating Brownian noise 1.6-fold and absorption to 7 ppm at 1064 nm

The design embeds a resonant metasurface layer below the multilayer stack rather than at the input face, shielding the lossy resonant elements from peak intracavity intensity. A new coherent noise model combines beam-scale mean-field thermoelastic fluctuations with sub-wavelength periodic responses, yielding the 1.6-fold noise reduction at 1064 nm for a target reflectance. Angular tolerance improves, maintaining high reflectance over a 1-degree range compared with bare metasurface mirrors.

Precision optical cavities underpin gravitational-wave detectors, optical atomic clocks, and emerging quantum networks; coating Brownian noise currently limits their length stability at room temperature. By relocating the metasurface, the hybrid approach decouples low-noise performance from the high-loss penalty that has blocked earlier all-metasurface proposals. The 7 ppm absorption figure remains above the best ion-beam-sputtered coatings but is low enough for many high-finesse applications.

No experimental cavity test yet exists; the work is purely computational. Validation will require fabricating the buried metasurface, measuring scatter and absorption in a Fabry-Perot cavity, and confirming the predicted noise spectrum via direct thermal-noise readout. Success would immediately affect LIGO A+ upgrades and next-generation clock lasers.

Future work should benchmark against crystalline coatings and explore cryogenic operation, where thermoelastic noise mechanisms change.