Breaking the Energy-Symmetry-Based Propagation Growth Blockade in Magneto-Optical Rotation

The magneto-optical polarization rotation effect has myriad applications in many research areas spanning the scientific spectrum, including space and interstellar research, nanotechnology, material science, biomedical imaging, and subatomic particle research. In the nonlinear magneto-optical rotation (NMOR) effect, the angle of rotation of a linearly polarized optical field in a magnetized medium is dependent upon its intensity. However, typical NMOR signals of conventional single-beam $\text{Λ}$-scheme atomic magnetometers are peculiarly small, requiring sophisticated magnetic shielding and high-frequency phase-sensitive detection. Here, we show the presence of an energy-symmetry-based propagation growth blockade that undermines the NMOR effect in conventional single-beam $\text{Λ}$-scheme atomic magnetometers. We further demonstrate, both experimentally and theoretically, an inelastic wave-mixing technique that breaks this NMOR blockade, resulting in more-than-2-orders-of-magnitude enhancement of the NMOR signal power amplitude that cannot be achieved with conventional single-beam $\text{Λ}$-scheme atomic magnetometers. This technique, demonstrated here with substantially reduced light intensities at near-room temperatures, may lead to many applications, especially in the field of biomagnetism and high-resolution low-field magnetic imaging.