Ultra-thin pancake beam expanding collimator with metalens for atomic magnetometer

Optically pumped atomic magnetometers (OPAMs), as cutting-edge sensing technology, demonstrate immense value in fields such as biomedical imaging and geological exploration due to their ultra-high sensitivity and miniaturization potential. However, traditional optical systems, due to their large size and complex components, severely limit the portability and measurement accuracy of the devices. A polarization-selective metalens is included in an ultra-thin pancake beam expanding collimator, which allows for a reduction in optical path length while preserving high collimation performance. At 795 nm, the metalens forms a folded metacavity with a plane mirror and exhibits spin-dependent reflection and transmission. When used in an atomic magnetometer, the collimator reduces the module volume to 27 % of traditional designs while maintaining fT-level sensitivity—a crucial feature for geophysical and biological applications. This research not only breaks through the technological bottleneck of miniaturizing atomic magnetometers but also pioneers a new paradigm of chip-integrated optical systems for atomic sensors.