Two-photon electromagnetic induction imaging with an atomic magnetometer

Electromagnetic induction imaging (EMI) is a contactless, nondestructive evaluation technique based on sensing the response of target to oscillating magnetic fields as they penetrate into materials. Leveraging enhanced performance radio frequency atomic magnetometers (RF-AMs) at low frequencies can enable highly sensitive through-barrier EMI measurements, which, for example, reveal concealed weaponry or inspect subsurface material defects. However, deriving this advantage requires precise control well-defined, bias field with respect background texture, which presents cumbersome challenge stabilize in real-world unshielded scenarios. Here, we implement two-photon RF-AM scheme portable setup bypass requirement and achieve stable, repeatable resonances sub-kHz regime. The improved accessibility lower primary offer greater skin-depth materials facilitates an enhancement factor 8 skin penetration system, detecting features behind Al shield 3.2 mm. also reduces need large compensation coils field, facilitating implementation compact devices.