Three-Dimensional Radiative Heat Transfer Including Polarization

随着激光技术的发展，单色辐射偏振光束与散射材料的相互作用问题在热传导界得到了相当大的重视。激光现在被用作诊断工具来探测热燃烧气体和大气，并测量填充床、隔热材料、陶瓷和人体组织的辐射特性。基于激光的微加工系统在微电子工业中广泛应用，在微机械结构制造方面具有巨大的潜力。激光的医学应用范围从治疗心脏病和癌症到牙科和眼科手术。利用激光束作为“镊子”抓住并操纵活细胞片段，被认为是一种改进基因定位方法的方法。由于激光光束的尺寸有限，而且是线偏振的，因此这些应用大多必须归类为多维的，而且它们往往涉及多重散射和各向异性散射。目前确实需要发展一种辐射传输的理论模型，使其能够包括所有这些因素，并制定处理极化效应的准则和近似程序。本课题是对三维辐射传热的理论和实验研究，包括极化和多次散射。具体来说，多次散射对已知偏振（线性、圆形或椭圆）激光束的影响正在研究中。激光束垂直于圆柱形散射介质的顶部平坦表面入射。散射中心是均匀的球形粒子，在介质中随机分布。基于斯托克斯参数的三维矢量输运方程，建立了一个理论模型。通常的散射相位函数将被一个4x4相位矩阵所取代。利用双傅立叶变换方法将输运方程简化为一维形式，用Ambartsumian方法求解得到的方程。然后使用双重傅里叶反变换计算背散射辐射。首先对小的球形粒子进行理论分析，即瑞利散射。将进行一系列精心控制的实验，将乳胶微球悬浮在纯水中以验证理论模型。微球的浓度会发生变化，因此散射介质的光学厚度会从薄到厚。这项研究的结果将为涉及偏振激光束与散射介质相互作用的许多实际问题提供见解。一个更真实的辐射模型的发展应该在许多领域有重大的影响，其中激光被利用，包括传热，制造和医学。

With the development of the laser the problem of the interaction of a polarized beam of monochromatic radiation with a scattering material has gained considerable importance in the heat transfer community. Lasers are now used as diagnostic tools to probe hot combustion gases as well as the atmosphere, and to measure the radiative properties of packed- beds, thermal insulations, ceramics, and human tissue. Laser- based micromachining systems abound in the microelectronics industry and hold great potential in the fabrication of micromechanical structures. The medical applications of lasers range from treating heart disease and cancer to dentistry and eye surgery. The use of laser beams as "tweezers" to seize and manipulate bits of living cells is being considered as a way to improve gene-mapping methods. Most of these applications must be classified as multidimensional because of the finite size of the laser beam which is linearly polarized, and they often involve multiple and anisotropic scattering. A definite need exists to develop a theoretical model for radiative transfer that can incorporate all these factors and to develop guidelines and approximate procedures for handling polarization effects. This project is a theoretical and experimental study of three- dimensional radiative heat transfer including polarization and multiple scattering. Specifically, the effects of multiple scattering on a laser beam of known polarization (linear, circular, or elliptical) are under investigation. The laser beam is incident perpendicular to the top, flat surface of a cylindrical scattering medium. The scattering centers are homogeneous spherical particles which are randomly distributed within the medium. A theoretical model is being developed based on the three-dimensional vector transport equation for the Stokes parameters. The usual scattering phase function will be replaced by a 4x4 phase matrix. The transport equation will be reduced to a one-dimensional form using the double Fourier transform method, and the resulting equation will be solved by Ambartsumian's method. The back-scattered radiation will then be calculated using a double inverse Fourier transform. The theoretical analysis will be first carried out for small spherical particles, i.e., Rayleigh scattering. A series of carefully controlled experiments will be conducted with latex microspheres suspended in pure water to validate the theoretical model. The concentration of the microspheres will be varied so that the optical thickness of the scattering medium will range from thin to thick. The results of this research will provide insight into a number of practical problems involving the interaction of a polarized laser beam with a scattering medium. The development of a more realistic radiation model should have a significant impact in many fields where lasers are utilized including heat transfer, manufacturing, and medicine.