South China Normal University, MOE Key Laboratory of Laser Life Science, Tianhe Shipai, Guangzhou, Guangzhou 510631 China.
J Biomed Opt. 2011 Jul;16(7):075001. doi: 10.1117/1.3596174.
A theoretical model that deals with SHG from crystallized type I collagen fiber formed by a bundle of fibrils is established. By introducing a density distribution function of dipoles within fibrils assembly into the dipole theory and combining with structural order (m,l) parameters revealed by quasi-phase-matching (QPM) theory, our established theoretical model comprehensively characterizes both biophysical features of collagen dipoles and the crystalline characteristics of collagen fiber. This new model quantitatively reveals the 3-D distribution of second-harmonic generation (SHG) emission angle (θ,ϕ) in accordance with the emission power. Results show that fibrils diameter d(1) and structural order m, which describes the structural characteristics of collagen fiber along the incident light propagation direction has significant influence on backward∕forward SHG emission. The decrease of fibrils diameter d(1) induces an increase of the peak SHG emission angle θ(max). As d(1) decreases to a threshold value, in our case it is around d(1) = 150 nm when (m,l) = (1,0), θ(max) > 90 deg, indicating that backward SHG emission appears. The SHG may have two symmetrical emission distribution lobes or may have only one or two unsymmetrical emission lobes with unequal emission power, depending on the functional area of (m,l) on d(1).
建立了一个处理由原纤维束形成的结晶 I 型胶原纤维的二次谐波产生 (SHG) 的理论模型。通过在偶极子理论中引入原纤维组装内偶极子的密度分布函数，并结合准相位匹配 (QPM) 理论揭示的结构序参数 (m，l)，我们建立的理论模型全面描述了胶原偶极子的生物物理特征和胶原纤维的晶体特征。该新模型根据发射功率定量揭示了二次谐波产生 (SHG) 发射角 (θ，ϕ) 的 3D 分布。结果表明，描述胶原纤维沿入射光传播方向的结构特征的原纤维直径 d(1)和结构序 m 对反向/正向 SHG 发射有显著影响。原纤维直径 d(1) 的减小会导致峰值 SHG 发射角 θ(max)的增加。当 d(1)减小到一个阈值时，在我们的情况下，当 (m，l) = (1，0) 时，d(1)约为 150nm，θ(max)>90 度，表明出现反向 SHG 发射。SHG 可能具有两个对称的发射分布瓣，或者可能只有一个或两个不对称的发射瓣，发射功率不等，这取决于 (m，l) 在 d(1)上的功能区域。
