Diffuse back-illumination setup for high temporally resolved extinction imaging.
Diffuse back-illumination setup for high temporally resolved extinction imaging.
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DOI：
10.1364/ao.56.005028
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发表时间：
2017-06
期刊：
影响因子：
1.9
通讯作者：
F. R. Westlye;Keith Penney;Anders Ivarsson;L. Pickett;J. Manin;S. Skeen
中科院分区：
文献类型：
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作者：
F. R. Westlye;Keith Penney;Anders Ivarsson;L. Pickett;J. Manin;S. Skeen
这项工作介绍了在恶劣的光学环境中用于定量的、高时间分辨率的视线消光成像的光学装置的发展。该应用程序专门针对高环境温度和压力条件下的汽车燃油喷雾测量，在这些条件下，时间尺度很短，沿光路的折射率梯度(即光束转向)的可感知衰减可能会很明显。对照明和收集光学进行了优化，以减小光束转向，设计准则得到了完善的理论关系的支持。使用简单的光线跟踪从概念上解释了折射导向的一般效果。分析了三个独立的场景，以确定使观测到的辐射通量不受转向效应影响所需的照明特性。这些标准用于优化光学系统中的光吞吐量，从而实现最小曝光时间和高时间分辨率能力。该装置使用定制的工程漫射器在有限的角度范围内传输恒定的辐射，从而使辐射强度最大化，同时满足最佳波束控制抑制的照明标准。详细介绍了光学系统的完整表征方法。给出了汽液边界和汽车喷雾中碳烟体积分数的测量结果，证明了改进的对比度和降低的不确定度。与以前的高时间分辨率设置相比，当前的光学设置将由折射率梯度引起的衰减减少了一个数量级。
This work presents the development of an optical setup for quantitative, high-temporal resolution line-of-sight extinction imaging in harsh optical environments. The application specifically targets measurements of automotive fuel sprays at high ambient temperature and pressure conditions where time scales are short and perceived attenuation by refractive index gradients along the optical path (i.e., beam steering) can be significant. The illumination and collection optics are optimized to abate beam steering, and the design criteria are supported by well-established theoretical relationships. The general effects of refractive steering are explained conceptually using simple ray tracing. Three isolated scenarios are analyzed to establish the lighting characteristics required to render the observed radiant flux unaffected by the steering effect. These criteria are used to optimize light throughput in the optical system, enabling minimal exposure times and high-temporal resolution capabilities. The setup uses a customized engineered diffuser to transmit a constant radiance within a limited angular range such that radiant intensity is maximized while fulfilling the lighting criteria for optimal beam-steering suppression. Methods for complete characterization of the optical system are detailed. Measurements of the liquid-vapor boundary and the soot volume fraction in an automotive spray are presented to demonstrate the resulting improved contrast and reduced uncertainty. The current optical setup reduces attenuation caused by refractive index gradients by an order of magnitude compared to previous high-temporal resolution setups.