Phase matching considerations in second harmonic generation from tissues: Effects on emission directionality, conversion efficiency and observed morphology
Phase matching considerations in second harmonic generation from tissues: Effects on emission directionality, conversion efficiency and observed morphology
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DOI：
10.1016/j.optcom.2007.10.040
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发表时间：
2008-04-01
影响因子：
2.4
通讯作者：
Campagnola, Paul J.
中科院分区：
文献类型：
--
作者：
LaComb, Ronald;Nadiarnykh, Oleg;Campagnola, Paul J.
我们提出了一个启发式的治疗，涉及SHG图像强度，信号方向性，观察到的形态胶原蛋白和纤维素纤维组织的物理结构。SHG创建模型是基于宽松的相位匹配条件，该条件考虑了来自介质的色散、随机性和轴向动量贡献，并且包括数学处理，该数学处理将SHG转换效率与原纤维直径和填充相关联，该数学处理通过包括由准相位匹配（QPM）产生的潜在强度放大。这个理论的一个直接结果是，在生物组织中的SHG不是严格的相干过程，并且前向SHG具有比后向分量更长的相干长度。通过这种处理，我们表明，发射方向性和转换效率并不仅仅取决于纤维的大小，而且还取决于纤维间结构的堆积密度和顺序。我们在比较正常和成骨不全（01）皮肤的SHG反应中证明了这些原理。我们发现，在患病状态下观察到的方向性和相对强度下降是一致的相位匹配条件所产生的原纤维的大小和更随机的组装。我们进一步使用这一理论来解释在纤维组织中向前和向后收集的SHG中观察到的形态学差异（例如，胶原和纤维素）。具体来说，我们属性分割外观之间的破坏性干扰小纤维分离小于相干长度。我们建议的方法的基础上放松相位匹配条件是一般在预测组织中的SHG响应，并可能广泛适用于解释诊断应用的SHG对比。(C)2007 Elsevier B.V.保留所有权利。
We present a heuristic treatment which relates SHG image intensities, signal directionality, and observed morphology to the physical structure of collagen and cellulose fibrillar tissues. The SHG creation model is based upon relaxed phase matching conditions which account for dispersion, randomness, and axial momentum contributions from the media, and includes a mathematical treatment which relates SHG conversion efficiency to fibril diameter and packing through the inclusion of potential intensity amplification resultant from quasi-phase matching (QPM). A direct consequence of this theory is that SHG in biological tissues is not strictly a coherent process, and that the forward directed SHG has a longer coherence length than the backward component, Through this treatment, we show that the emission directionality and also conversion efficiency do not arise solely from the fibril size but also depend on packing density and order of the inter-fibril structure. We demonstrate these principles in comparing the SHG response in normal and Osteogenesis Imperfecta (01) skin. We show that the observed directionality and decreased relative intensity in the diseased state is consistent with phase matching conditions arising from the decreased fibril size and more random assembly. We further use this theory to explain the differences in morphology seen in forward and backward collected SHG in fibrillar tissues (e.g., collagenous and cellulosic). Specifically, we attribute segmented appearance to destructive interference between small fibrils separated by less than the coherence length. We suggest the approach based on relaxed phasematching conditions is general in predicting the SHG response in tissues and may be broadly applicable in interpreting the SHG contrast for diagnostic applications. (C) 2007 Elsevier B.V. All rights reserved.