Faraday rotation density measurements of optically thick alkali metal vapors

We investigate the measurement of alkali number densities using the Faraday rotation of linearly polarized light. We find that the alkali number density may be reliably extracted even in regimes of very high buffer gas pressure, and very high alkali number density. We have directly verified our results in potassium using absorption spectroscopy on the second resonance (42S→52P)