Determination of atomic number densities of ⁸⁷Rb and ³He based on absorption spectroscopy

The atomic number densities of ⁸⁷Rb vapor and surrounding gas ³He in a sealed cubic cell were measured by sweeping the absorption line and fitting the experimental data with a Lorentzian profile. The absorption was carried out around the D1 transition at different temperatures. We compare our results for the number density for ⁸⁷Rb with the previous methods and calculate the fractional error to be less than 5% as well as the error for ³He between this work and the density obtained from the filling procedure to be no more than 4.2% at 370K. In addition, we discuss the factors that contribute to the error, among which the cell temperature plays the most important role.