Laser-Assisted Diamond Cutting for Low-Damage Fabrication of High-Q CaF₂ Whispering-Gallery Mode Resonators

Calcium fluoride (CaF₂) crystals are an ideal material for fabricating high-quality whispering-gallery-mode (WGM) optical resonators. However, their hard and brittle nature make it difficult to achieve low-damage, ultra-smooth surfaces through conventional cutting, which limits the optical performance of the resonators. To address this, laser-assisted diamond cutting technology is proposed in this study for low-damage and high-quality fabrication. Molecular dynamics simulations reveal the atomic-scale mechanism by which laser thermal effects reduce cutting forces and promote dislocation motion. Nano-scratch experiments further show that the critical depth of ductile-brittle transition (DBT) increases from 388 nm to 1070 nm, 2.76 times that of conventional cutting. Based on these results, ultra-precision turning of a high-quality hemispherical resonator with a Q factor of up to 1.3 × 10⁸ was achieved. This study provides an effective solution for low-damage and high-performance resonator fabrication from hard and brittle optical crystals.