Laser threshold magnetometry

Abstract

We propose a new type of sensor, which uses diamond containing the optically active nitrogen-vacancy (NV ^− ) centres as a laser medium. The magnetometer can be operated at room-temperature and generates light that can be readily fibre coupled, thereby permitting use in industrial applications and remote sensing. By combining laser pumping with a radio-frequency Rabi-drive field, an external magnetic field changes the fluorescence of the NV ^− centres. We use this change in fluorescence level to push the laser above threshold, turning it on with an intensity controlled by the external magnetic field, which provides a coherent amplification of the readout signal with very high contrast. This mechanism is qualitatively different from conventional NV ^− –based magnetometers which use fluorescence measurements, based on incoherent photon emission. We term our approach laser threshold magnetometer (LTM). We predict that an NV ^− –based LTM with a volume of 1 mm ^3 can achieve shot-noise limited dc sensitivity of 1.86 fT $/\sqrt{{\rm{Hz}}}$ and ac sensitivity of 3.97 fT $/\sqrt{{\rm{Hz}}}$ .

Keywords

• magnetometry
• nitrogen-vacancy centre
• lasing
• sensing