Chemical–mechanical surface treatment method for high-quality crystalline whispering gallery mode microresonators

Subject of study. A novel method for the surface treatment of high-quality crystalline optical microresonators with whispering gallery modes (WGMs) based on chemical-mechanical polishing using magnesium fluoride microresonators is proposed. The proposed method can be applied to brittle and soft materials. Aim of study. The study aimed to develop a new effective method for the surface treatment of crystalline WGM microresonators based on asymptotic chemical-mechanical polishing. Methods. Magnesium fluoride resonators fabricated by diamond turning were polished using the chemical-mechanical polishing process. The values of the quality factor (Q-factor) and roughness were measured using independent methods to determine the numerical relationship between them: roughness was measured using an interference microscope, and the Q-factor was determined based on the half-width of the resonant power dip at critical coupling. The focus was on the investigation of the properties of the polished suspension: the size distribution of the suspended particles was determined before polishing using the dynamic light scattering method and a scanning electron microscope. Main results. A novel surface treatment method for high-quality crystalline optical WGM microresonators that reduces the polishing time by at least three times has been developed and successfully applied. The proposed method ensures the fabrication of resonators with a small radius and a Q-factor of at least 1 x 10(9) and helps maintain their shapes. The surface roughness along the resonator generatrix after chemical-mechanical polishing was similar to 5 nm, which corresponds to 1-1.5 unit cells of the crystal. Practical significance. The chemical-mechanical polishing method helps reduce the polishing time and improve the surface quality of complex structures. In addition, it can facilitate the automation of the microresonator fabrication process. (c) 2023 Optica Publishing Group