Ion Current as a Precise Measure of the Loading Rate of a Magneto-Optical Trap

We have demonstrated that the ion current resulting from collisions between metastable krypton atoms in a magneto-optical trap can be used to precisely measure the trap loading rate. We measured both the ion current of the abundant isotope $^{83}$Kr (isotopic abundance $=$ 11{\%}) and the single-atom counting rate of the rare isotope $^{85}$Kr (isotopic abundance $\sim$ 1 $\times$ 10$^{-11})$, and found the two quantities to be proportional at a precision level of 0.9{\%}. This work results in a significant improvement in using the magneto-optical trap as an analytical tool for noble-gas isotope ratio measurements, and will benefit both atomic physics studies and applications in the earth sciences. Reference: Opt. Lett. \textbf{39}, 409 (2014).