Angular and Polarisation Correlations between Cascade Photons

The density matrix theory is applied to establish a connection between the configuration of the excited atomic states and the intensity and polarisation of the cascade photons emitted during the decay process. Explicit expressions are obtained for the P, D and F states of hydrogen and helium atoms. These formulae can be used to assist experimental design for the most efficient and revealing measurements. In addition, formulae for the integrated polarisation of the emitted photons from the P, D, F and G states of hydrogen and helium are presented in terms of partial excitation cross sections.