Absolute alkali-metal polarization using transmission methods.

We report measurements of optical transmission through a 1 cm square Rb-Xe vapor cell near the D1 transition as a function of incident optical power and cell temperature. Low-power absorption spectra are used to determine the optical depth at multiple temperatures, providing a baseline for unsaturated absorption. With the laser held at a fixed detuning and circular polarization, the transmitted power is recorded while sweeping the incident power from the weak-probe regime into strong optical driving.

 

At elevated optical depths, the transmission exhibits a strong nonlinear dependence on optical power, consistent with an intensity-dependent reduction in absorption in an optically thick spin-polarized medium. The data are analyzed using a simple propagation model, which yields an analytic Lambert-W expression for the transmitted power in the limit that diffusion can be neglected. Using independently measured optical depths and transmission curves, we infer an effective, path-averaged absolute rubidium polarization along the optical axis as a function of input power and temperature. This work demonstrates a transmission-based method for inferring average rubidium polarization in high optical depth vapor cells, offering a simple diagnostic complementary to more conventional polarization probes.