The early stage of spray atomization has been the subject of extensive research efforts, and while early breakup often focuses on engineering sprays, the very same dynamics are important in medical sprays and natural spray generation. In the region of primary atomization ancillary droplets create a shroud with high optical scattering properties (i.e., high optical depth, OD, even over small physical distance) that surrounds the bulk atomizing core. The atomization process has been predicted by models and numerical simulations but there is a lack of experimental data in the early breakup region as a source for verification and validation of those models. Ultra-Short Pulse Off-Axis Digital Holography (USPODH) allows the imaging of a target hidden in an optically dense turbid environment. The technique uses short coherence length femtosecond laser pulses to con-struct images from only ballistic and quasi-ballistic photons. Prior work demonstrated the feasibility of USPODH imaging in ambient and realistic conditions with OD up to 12. The current work expands the technical aspects from the previous study, particularly enhancing the field-of-view by adopting a lensed long-range microscopy setup. The achieved magnification is between 1.1 and 1.5, at a working distance of 35cm, and resolves primary atomization lobes, ligaments, and droplets as small as 14 µm in the near-nozzle region. USPODH is successfully rejecting light scattered by the shroud of primary atomization droplets surrounding the spray core and can image fluid struc-tures at the gas-to-liquid interface which are consistent with the structures predicted by primary atomization models.

中文翻译：

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使用超短脉冲离轴数字全息术对光密喷雾结构进行远程显微镜检查

喷雾雾化的早期阶段一直是广泛研究的主题，虽然早期分解通常集中在工程喷雾上，但同样的动力学在医用喷雾和天然喷雾生成中也很重要。在初级雾化区域，辅助液滴形成一个具有高光学散射特性（即高光学深度，OD，甚至在很小的物理距离上）的护罩，它围绕着本体雾化核心。原子化过程已通过模型和数值模拟进行预测，但缺乏早期分解区域的实验数据作为验证和验证这些模型的来源。超短脉冲离轴数字全息 (USPODH) 允许对隐藏在光密混浊环境中的目标进行成像。该技术使用短相干长度的飞秒激光脉冲仅从弹道和准弹道光子构建图像。先前的工作证明了 USPODH 在 OD 高达 12 的环境和现实条件下成像的可行性。当前的工作扩展了先前研究的技术方面，特别是通过采用透镜远程显微镜设置来增强视野。获得的放大倍数在 1.1 到 1.5 之间，工作距离为 35 厘米，可分辨喷嘴附近区域中小至 14 µm 的初级雾化瓣、韧带和液滴。