Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays
Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays
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DOI：
10.1007/s00348-017-2396-9
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发表时间：
2017-09-01
影响因子：
2.4
通讯作者：
Berrocal, Edouard
中科院分区：
文献类型：
--
作者：
Mishra, Yogeshwar Nath;Kristensson, Elias;Berrocal, Edouard
由于检测到多重光散射，因此通过光学密集喷雾进行成像具有挑战性，这会使记录的图像模糊并限制能见度。结构激光照明平面成像（SLIPI）是一种能够减少光片成像配置中由多次散射引起的强度贡献的技术。传统的SLIPI方法是基于连续记录三个调制子图像，每个子图像具有不同的空间相位，因此主要用于时间平均成像。为了规避这种限制和图像喷射动力学，最近开发了“瞬时”两相（2p）和单相（1p） SLIPI方法。本文的目的是比较这两种方法在光学设计、图像后处理程序、多重散射抑制能力和空间分辨率方面的差异。采用这两种方法对瞬态直接喷射火花点火乙醇喷雾进行成像，用于液体激光诱导荧光和Mie散射检测。本文还利用蒙特卡罗模拟方法对多重散射抑制和图像形成的能力进行了数值模拟。本文表明，这两种方法都有效地抑制了多次光散射的贡献，提供了与相应的单次散射情况接近的图像强度轮廓。在实验中，这种抑制既提高了图像对比度，又消除了不希望被解释为信号的杂散光成分。然而，虽然2p-SLIPI保留了大部分初始空间分辨率，但1p-SLIPI会导致空间分辨率的损失，其中高频图像信息不再可见。因此，在保留喷雾结构的最详细信息（使用2p-SLIPI）和能够仅从单个调制图像记录SLIPI图像（使用1p-SLIPI）之间存在权衡。本文提出的这两种方法的比较和技术概述有助于选择哪种方法最适合给定的喷雾可视化应用。
Imaging through optically dense sprays is challenging due to the detection of multiple light scattering, which blurs the recorded images and limits visibility. Structured laser illumination planar imaging (SLIPI) is a technique that is capable of reducing the intensity contribution that stems from multiple scattering in a light sheet imaging configuration. The conventional SLIPI approach is based on recording three modulated sub-images successively, each having a different spatial phase, and has, therefore, been mostly used for temporally averaged imaging. To circumvent this limitation and image spray dynamics, 'instantaneous' two-phase (2p) and single-phase (1p) SLIPI approaches have recently been developed. The purpose of the work presented here is to compare these two approaches in terms of optical design, image post-processing routines, multiple scattering suppression ability, and spatial resolution. The two approaches are used to image a transient direct-injection spark-ignition ethanol spray, for both liquid laser-induced fluorescence and Mie scattering detection. The capabilities of the approaches for multiple scattering suppression and image formation have also been numerically modeled by means of Monte Carlo simulation. This article shows that both approaches efficiently suppress the contribution from multiple light scattering, providing images with an intensity profile close to the corresponding single scattering case. Experimentally, this suppression renders both an improvement in image contrast and the removal of undesired stray light components that could be interpreted as signal. However, while 2p-SLIPI preserves most of the initial spatial resolution, 1p-SLIPI results in a loss of spatial resolution, where high-frequency image information is not visible anymore. Thus, there is a trade-off between preserving the most detailed information of the spray structure-with 2p-SLIPI-and being able to record an SLIPI image from a single modulated image only-with 1p-SLIPI. The comparison and technical overview of these two methods presented in this paper can facilitate in selecting which approach is the most suitable for a given application for spray visualization.