Alleviating optical pumping inhomogeneity using a polarization-encoded metasurface in NMR co-magnetometers.

In nuclear magnetic resonance (NMR) co-magnetometers, the non-uniform transverse energy distribution of the pumping Gaussian beam can result in substantial optical pumping inhomogeneity and decoherence of atomic spins, which hinder the improvement of the precision and sensitivity of the sensor. One of the most significant recent technological advances for laser beam homogenization is the utilization of the microlens array system. However, the homogenized characteristics of the microlens array system vary with the propagation distance of the pumping light and are not suitable for chip integration, which will affect the sensitivity and compactness of the NMR system. To solve this issue, a metasurface homogenizer is demonstrated for encoding intensity information into the polarization profile of an incident Gaussian beam by combining the geometric phase and Malus' law with the transverse intensity distribution independent of the propagation distance. Compared to Gaussian beam pumping at identical input power, the metasurface homogenizer enhances the measured optical magnetic sensitivity by 23%. The proposed metasurface homogenizer not only realizes the higher precision and sensitivity in NMR co-magnetometers, but also highlights how metasurface-based technologies can contribute to the integrated quantum sensing regime.