Vector light shift averaging in paraffin-coated alkali vapor cells.

Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin-coherence time in paraffin-coated cells leads to spatial averaging of the vector light shift over the entire cell volume. This renders the averaged vector light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. Importantly, the demonstrated averaging mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.

Dual-Axis π-Pulse Magnetometer with Suppressed Spin-Exchange Relaxation.

We present a spin-exchange relaxation-free vector magnetometer with suppressed 1/f probe noise, achieved by applying a small dc bias field and a comb of magnetic dc π pulses along the pump direction. This results in a synchronous orthogonal ac response for each of its two sensitive axes. The magnetometer is particularly well suited to applications such as biomagnetism in which the signal to be measured carries a dominant component of its power at low frequencies. The magnetometer reaches a technical noise floor of 8 .4 fT Hz -1/2   ( x ^ ) and 11 fT Hz -1/2   ( y ^ ) at 0.01 Hz. A single-axis dc spin-exchange relaxation-free (SERF) magnetometer sharing the same experimental apparatus attains 61 fT Hz-1/2 at the same frequency. A noise minimum of 1 .1 fT Hz -1/2   ( x ^ ) and 2 .0 fT Hz -1/2   ( y ^ ) is reached by the magnetometer at10 Hz, compared to 0.7 fT Hz-1/2 at 25 Hz for a dc SERF magnetometer.