Precision measurements of optically thick alkali metal number density within a hybrid alkali metal cell.

The number density of alkali metal vapors and their ratio within hybrid cells is of great significance for the optimal rotation sensitivity of alkali metal-noble gas comagnetometers. To measure the number density of optically thick Rb vapor accurately within a hybrid cell containing optically thin K vapor and optically thick Rb vapor, a novel method combining alkali metal absorption spectroscopy and Raoult's law is proposed in this paper. The relative error between experimental results and results calculated by empirical formula is within ±5% from 365 to 450 K, and the measurement accuracy is improved more than 10 times compared to previous study. This novel method could be applied to check the number density ratio of alkali metal within hybrid cells more precisely.