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arXiv · 2609.15351

State-Dependent Diffusion and Spectra of Strongly Driven Thermal Atoms

Zheng Xiao·Zijie Liu·Suyang Wei·Anhong Dang·Tiantian Shi·Jingbiao Chen
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Abstract

We propose a state-dependent diffusion model for strongly driven thermal-atom spectra. Starting from the trajectory-dependent internal-state evolution of individual atoms, we derive a closed spatial equation for the local density-matrix field using a velocity-moment expansion. Measurements of an $^{85}$Rb atomic-filter transmission spectrum agree well with the model up to a maximum Gaussian peak intensity of $1.27\times10^{3}$ W/cm$^2$, approaching six orders of magnitude above the $^{85}$Rb D2-line saturation intensity. Counterintuitively, the model reveals an anomalous optical-pumping pathway in which intense light transfers atoms from nominally dark states into bright states. Hyperfine Paschen--Back splitting selectively enhances this anomalous pathway while suppressing conventional optical pumping, allowing the filter to maintain approximately 97$\%$ transmission at the highest intensity studied. This work provides a framework for controlling strongly driven atomic ensembles and designing saturation-resistant atomic optical devices.

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Zheng Xiao, Zijie Liu, Suyang Wei, Anhong Dang, Tiantian Shi, Jingbiao Chen. 2026-09-14. State-Dependent Diffusion and Spectra of Strongly Driven Thermal Atoms. https://arxiv.org/abs/2609.15351

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