Picotesla-sensitivity microcavity optomechanical magnetometry.

Area of Science:

• Physics
• Materials Science
• Engineering

Background:

• Cavity optomechanical systems enhance magnetic field sensing through optical and mechanical resonance.
• Previous microcavity optomechanical magnetometry (MCOM) using Terfenol-D films had limited sensitivity (585 pT Hz^-1/2).

Purpose of the Study:

• To develop a high-sensitivity, mass-producible MCOM by employing FeGaB thin films on SiO₂ WGM microdisks.
• To theoretically explore magnetic actuation and noise-limited sensitivity by varying film and microdisk parameters.
• To demonstrate real-time pulsed magnetic field measurement for applications like corona current monitoring.

Main Methods:

• Sputtering FeGaB thin films onto high-Q SiO₂ whispering gallery mode (WGM) microdisks.
• Fabricating and characterizing multiple magnetometers with varying radii and film thicknesses.
• Conducting theoretical studies on magnetic actuation constant and noise-limited sensitivity.

Main Results:

• Achieved a peak sensitivity of 1.68 pT Hz^-1/2 at 9.52 MHz using a 355 μm radius microdisk and 1.3 μm thick FeGaB film.
• Demonstrated over two orders of magnitude sensitivity improvement compared to previous Terfenol-D sputtered films.
• Operated without a bias magnetic field due to FeGaB's soft magnetic properties.

Conclusions:

• The FeGaB-based MCOM offers a significant advancement in magnetic field sensing sensitivity and performance.
• The developed magnetometer is suitable for real-time pulsed magnetic field measurements, such as corona current in high-voltage lines.
• High-sensitivity magnetometers show potential for applications in magnetic induction tomography and corona current monitoring.