2025/03/12 by Catriona A. Thomson, Thomson, Catriona A., Michael E. Tobar +3
Engineering · #Acoustic Wave Resonator Technologies #Applied Physics (physics.app-ph) #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Optics (physics.optics)
paper · pdf · doi:10.48550/arxiv.2503.08981
openalex publication_date 2025/03/12 · openalex created_date 2025/10/13 · openalex updated_date 2026/07/28
We report the observation of transient nonlinear optical effects in a macroscopic whispering gallery mode resonator made of rutile TiO2, demonstrating strong optical-microwave transduction under laser irradiation. By comparing the effects of ultraviolet (UV, 385 nm) and near-infrared (NIR, 700 nm) radiation, we find that the UV-induced effects are significantly amplified, consistent with the material's semiconductor bandgap energy. The interaction results in frequency shifts of microwave modes and changes in quality factor, suggesting a localized saturable refractive index tuning. This may be attributed to the saturation of a spin transition of a dopant ion within the crystal lattice. Remarkably, these effects are observed at low optical powers, down to nanowatt levels, indicating high sensitivity and efficient of light-matter interaction in this system. The phenomenon is centered around 15 GHz, yet electron spin resonance measurements reveal no zero-field splitting at this frequency, suggesting an alternative mechanism beyond conventional spin resonance. These findings highlight the potential of low-power optical control of microwave modes in high-Q resonators for applications in quantum technologies, sensing, and reconfigurable photonic-microwave systems.