Abstract
We present here a novel framework within which the implementation of sub-Doppler cooling, in prevalent form manifest as polarisation gradient cooling, on atomic systems subsistent in both a free-space regime and one in the presence of a deep, far-off resonant dipole trap, can be fundamentally understood. We develop first a theoretical means through which the predicted presence or absence of atomic cooling, for an arbitrary frequency of an incident cooling field, on the D2 line of Rb-85 can be made. Following such a development, the framework itself is applied to both free-space atomic systems and those under which the imposition of a dipole potential is physically realised, in the pursuit of making transparent the mechanisms governing the integration of polarisation gradient cooling in a diverse array of systems. Excellent agreement is evinced between theory and experiment in all atomic systems investigated, suggesting that the theoretical framework developed provides an adequate description regarding the mechanisms of polarisation gradient cooling pertinent to its implementation on the D2 line of Rb-85