Near-resonance Light Scattering from a High-density, Ultracold Atomic ${}^{87}$Rb Gas

We report a combined experimental and theoretical investigation of near resonance light scattering from a high-density and ultracold atomic ${}^{87}$Rb gas. The atomic sample, having a peak density $\sim 5\cdot {10}^{13}$ atoms/cm${}^3$, temperature $\sim$ 65 $\mu$K and initially prepared in the F = 1 lower energy ${}^{87}$Rb hyperfine component, is optically pumped to the higher energy F = 2 hyperfine level. Measurements are made of the transient hyperfine pumping process and of the time evolution of scattering of near resonance probe radiation on the $F=2\to F^{\mathrm{\prime }}=3$ transition. Features of the density, detuning, and temporal dependence of the signals are attributed to the high density and consequent large optical depth of the samples.