利用密度-密度关联获得最佳聚焦的冷原子系统
Optimally focused cold atom systems obtained using density-density correlations
摘要：
共振吸收成像是一种常用的探测超冷原子系统二维柱密度的技术。在许多情况下，系统沿成像方向的厚度大大超过成像系统的景深，使得难以识别最佳聚焦配置。在这里，我们描述了一个系统的技术，使玻色-爱因斯坦凝聚体（BEC）和其他冷原子系统进入最佳焦点，即使在厚度与景深的比值很大时：在这个演示中，BEC的系数为8。该技术依赖于傅立叶变换的密度-密度关联函数（功率谱密度，PSD）中的散焦引起的伪影。这些伪影首次出现在PSD中的空间频率在聚焦时最大化;因此，聚焦过程识别并最大化PSD未被有限厚度效应污染的空间频率范围。
英文摘要：
Resonant absorption imaging is a common technique for detecting the two-dimensional column density of ultracold atom systems. In many cases, the system's thickness along the imaging direction greatly exceeds the imaging system's depth of field, making the identification of the optimally focused configuration difficult. Here we describe a systematic technique for bringing Bose-Einstein condensates (BEC) and other cold-atom systems into an optimal focus even when the ratio of the thickness to the depth of field is large: a factor of 8 in this demonstration with a BEC. This technique relies on defocus-induced artifacts in the Fourier-transformed density-density correlation function (the power spectral density, PSD). The spatial frequency at which these artifacts first appear in the PSD is maximized on focus; the focusing process therefore both identifies and maximizes the range of spatial frequencies over which the PSD is uncontaminated by finite-thickness effects.
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