物理学报2024，Vol.73Issue(14)：193-200,8.DOI:10.7498/aps.73.20240570
基于增强条纹去除的超冷原子成像
Ultracold atomic imaging based on enhanced fringe removal method
摘要
Abstract
Absorption imaging is the foundation for quantitative measurements in experiments on ultracold atoms.This technique mainly involves capturing images of both the probing light field and the atom absorption light field.In this process,the unavoidable jitter of the probing light introduces imaging noise of fringe patterns into the atomic optical density distribution OD.In conventional fringe removal algorithms,this type of noise can be normalized by constructing an optimal reference image from multiple reference images that have been actually taken,which shares similar fringe patterns to an absorption image(Fig.(a)).Although this method works well in the region without atomic signal,they often overlook the modulation of the noise signal due to atomic absorption effects,leading to persistent residual fringes on the atom clouds.This problem becomes more pronounced with atomic density increasing.Here,we propose an enhanced fringe removal algorithm that takes into account the effects of atomic absorption,and actively modulates the intensity of the noise signal in the reference image constructed by conventional fringe removal algorithms(Fig.(b)),effectively preventing the residual fringes from forming,thus significantly improving the signal-to-noise ratio of the atomic images.When applied to the absorption imaging of homogeneous Fermi gases with high density,as shown in Fig.(d),this new algorithm successfully reduces the relative standard deviation of optical depth characterizing atomic density fluctuations by approximately 37％,which is about 3 times the relative standard deviation by conventional algorithm.Three subgraphs in Fig.(e)show the optical depth distribution at corresponding data points labeled by square boxes in Fig.(d).Furthermore,we also use this technique to quantitatively determine the second sound in the unitary Fermi superfluid of 6Li atoms.Compared with conventional fringe removal methods,our new algorithm increases the correlation function's contrast of the density wave nearly 4 times,therefore enhancing the intensity of the density response spectrum by approximately 15％with half the measured standard error,paving the way for quantitatively determining the speed and attenuation of the second sound.These results demonstrate that the enhanced fringe removal algorithm not only effectively suppresses fringe noise,but also facilitates the identification and detection of important physical phenomena in high-density atomic systems,such as some collective excitations and new quantum phases.关键词
条纹去除/吸收成像/幺正费米超流/第二声波Key words
fringe removal/absorption imaging/unitary Fermi gases/second sound引用本文复制引用
王帅,李希,姚星灿..基于增强条纹去除的超冷原子成像[J].物理学报,2024,73(14):193-200,8.基金项目
国家自然科学基金(批准号:11874340)和国家重点研发计划(批准号:2018YFA0306501)资助的课题. Project supported by the National Natural Science Foundation of China(Grant No.11874340)and the National Key R&D Program of China(Grant No.2018YFA0306501). （批准号:11874340）
