  Alignment-based optically pumped magnetometers (OPMs) are capable of
measuring oscillating magnetic fields with high sensitivity in the fT/sqrt(Hz)
range. Until now, alignment-based magnetometers have only used paraffin-coated
vapour cells to extend the spin relaxation lifetimes of the alkali vapour. The
drawback of these cells is that they are hand-blown and are therefore
time-intensive, and somewhat unreliable, to produce. Buffer gas cells, on the
other hand, can be manufactured on a mass scale using microfabrication
techniques. We present the first demonstration of an alignment-based
magnetometer using a buffer gas vapour cell containing caesium (Cs) alkali
vapour and nitrogen (N2) buffer gas. The OPM is operated at 55 degrees C and we
achieve a 325 fT/sqrt(Hz) sensitivity to 10 kHz oscillating magnetic fields
with an 800 Hz bandwidth. The alignment-based magnetometer uses a single laser
beam for optical pumping and probing and could potentially allow for more rapid
commercialisation of radio-frequency OPMs, due to the robustness of the
one-beam geometry and the potential for mass-scale microfabrication of buffer
gas cells.
