Continuous High-Sensitivity and High-Bandwidth Atomic Magnetometer

Here we demonstrate an atomic magnetometer that has a bandwidth of more than 100 kHz and a sensitivity of 180 fT/root Hz at a Fourier frequency of 8 Hz, and 0.7 nT/root Hz at 100 kHz. These sensitivity measurements are achieved at geophysically useful magnetic field magnitudes (approximately 50 mu T inside a three-layer mu-metal shield) and are limited by the photon shot noise for frequencies above 8 Hz. This device is based on a nonlinear magneto-optical rotation sensor that is operated with an active feedback to the pump modulation frequency. We present a theoretical description of the response functions of the components in the magnetometer. We show that the range of operation of atomic magnetometers can thus be expanded beyond the conventional high-sensitivity, low-bandwidth domain, to provide a high-linearity, high-bandwidth, and high-sensitivity sensor.