Spatially resolved atomic dichroism and CPT-induced coherence-enhanced transmission in vector beam fields

In our previous studies, we reported polarization-dependent profile variations in modulation transfer spectroscopy, including enhanced error signals and modified absorption profiles, which could not be fully explained by conventional models. In this work, we propose a unified physical framework to interpret these phenomena by introducing the concept of atomic spatial polarization-dependent transmission. Using hybrid polarized vector beams as both pump and probe in a counter-propagating configuration, we demonstrate that polarization-induced anisotropic absorption arises from optical pumping dynamics mediated by the vector beam structure. We further show that, when coherent population trapping (CPT) is introduced via dual-frequency laser excitation, the formation of an atomic dark-state population markedly enhances transmission contrast and gives rise to pronounced spectral features. We observed that narrowing the full width at half maximum of the saturated absorption spectrum nearly doubled the MTS signal amplitude. These effects manifest as spatially modulated intensity patterns in the probe beam, thereby revealing CPT-enhanced, polarization-selective transmission in atomic media. Our results not only explain previously observed polarization-induced signal enhancements but also offer new insights into spatially coherent manipulation of atomic populations, with implications for precision spectroscopy and laser stabilization.