Radiation transport within the natural isotopic mixture of rubidium vapor after isotope selective excitation

Abstract

The radiation transport within the natural isotopic mixture of rubidium is studied by detecting the time dependent resonance fluorescence after isotope selective excitation of⁸⁷Rb or⁸⁵Rb to the 5² P _3/2 state by the pulsed light of a laser diode. At atomic densities of about 10¹² cm⁻³ the mean number of photon scatterings is 10 or 25 after excitation of⁸⁷Rb or⁸⁵Rb, respectively. Monte Carlo simulations of multiple photon scattering are used to reproduce the time dependent fluorescence signals. Satisfactory agreement between experiments and calculations can be achieved only if a radiative transfer of excitation energy between the different isotopes is considered. The energy transfer can be explained by radiative coupling of the different isotopes due to two partially overlapping hfs components of the 780 nm resonance line. As a test of our theoretical approach fluorescence signals recorded after excitation of⁸⁷Rb and⁸⁵Rb under identical experimental conditions are fitted both by using the same set of two parameters.