This thesis describes an investigation of Rydberg excitation within a high-density sample of cold strontium atoms. This sample is prepared using a two-stage magneto-optical trap, cooling first on a broad singlet transition and then a narrow triplet transition. Rydberg atoms are then created using a two-photon, three-level ladder type scheme and detected using a novel autoionisation technique. It is shown that, in the regime of high optical thickness on the probing transition, a significant Rydberg population can be created by photons that are multiply scattered before leaving the cloud.
The multiply scattered field is density-dependent and has strikingly different spectral properties from the incident laser light. This spectrum is convolved with the spectrum of the Rydberg atoms created via direct laser excitation and the two spectra can be isolated in post analysis. This technique provides a probe of the spectral distribution of the re-scattered light within the cloud, which may be qualitatively different from that of the transmitted light, and previously has not been measured directly. Additionally, this Rydberg population arising from the multiply scattered field can be seen in the spatial distribution of the Rydberg excitations within the atom sample. Finally, a careful analysis of the time dynamics of the Rydberg system reveals that multiple scattering co-exists with signatures of the Rydberg blockade in this strongly dissipative regime
