Subfemtotesla radio-frequency atomic magnetometer for detection of nuclear quadrupole resonance

A radio-frequency tunable atomic magnetometer is developed for detection of nuclear quadrupole resonance (NQR) from room temperature solids. It has a field sensitivity 0.24 fT Hz12 at the 423 kHz N14 NQR frequency of ammonium nitrate. A potential application of the magnetometer is detection of nitrogen-containing explosives which is difficult with conventional tuned copper coils due to a poor signal-to-noise ratio (SNR) below a few megahertz. The NQR signal from 22 g of powdered ammonium nitrate located 2 cm away from the sensor is detected with a SNR of 9 in a 4.4-s -long multiple echo sequence, which represents an estimated order-of-magnitude improvement in sensitivity over the pickup coil detection.