Abstract
Abstract This thesis is about “Production of a high-optical-density cold atom cloud”. In the experiment, Optical depth (OD) is an important parameter. The definition of OD is : OD = nσL, which n is density of atoms, σ is cross section and L is the length of media. The Slow effect in Elctromagnetically Induced Transparency needs larger optical depth to increase delay time which means how long the signal could pass through. In Quantum memory, the longer light storage have, the longer pulse width that atoms could save. In our lab, production of cold atoms cloud is much different from the past in this time. The major difference is trapping laser we used have much larger beam size and much larger power. In the past, the power was near to 100 mW, but in this time, the power we used is near to 330 mW, and beam size’s diameter is 30 mm. Because of higher power,we need to optimize the efficiency of MOPA which must have higher output power at lower injection power and the efficiency of coupling in bare fiber. Due to large beam size, the MOT system we erected may occur some problem. It may cause our cold atoms cloud becomes asymmetric. After solve problems about the shape of cloud, we use two-level system to estimate optical depth, and OD is near to 100 without any optimization(concentrate population, dark MOT, compress MOT and so on). The optimization need to be done after we ensure we can see EIT at high OD(~100). If we do so, OD may increase many times.