Remote Atmospheric Magnetometry

We are investigating an optical technique for remotely measuring nanotesla variations in the Earth's magnetic field ($\sim$ 0.5G). This technique uses a frequency-modulated, circularly polarized laser ($\lambda = $ 760 nm) to spin polarize the ground state of molecular oxygen at atmospheric conditions. The Earth's magnetic field splits the magnetic sublevels of molecular oxygen's ground state leading to spin depolarization. The molecule's fluorescence depends on the spin depolarization and consequently on the Earth's magnetic field. The time-dependent fluorescence will be extracted by heterodyning with the laser's frequency modulation. We will discuss limiting physical processes such as collisional dephasing, Doppler broadening, and molecular oxygen's magnetic dipole transition strength. This research is being funded by ONR.