Three-Dimensional Radiative Heat Transfer Including Polarization

随着激光器的发展，单色偏振光束与散射材料的相互作用问题在传热学领域得到了越来越多的重视。激光现在被用作诊断工具，用于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。基于激光的微机械加工系统在微电子工业中大量存在，在制造微机械结构方面具有巨大的潜力。激光的医疗应用范围从治疗心脏病和癌症到牙科和眼科手术。人们正在考虑使用激光作为“镊子”来捕捉和操纵活细胞的片段，以此来改进基因图谱的方法。这些应用中的大多数必须归类为多维，因为激光束的尺寸是有限的，它是线偏振的，而且它们经常涉及多次和各向异性散射。确实需要制定一种能够纳入所有这些因素的辐射传递理论模型，并制定处理偏振效应的准则和大致程序。本课题是对包括偏振和多次散射在内的三维辐射换热的理论和实验研究。具体地说，多重散射对已知极化(线性、圆形或椭圆形)的激光束的影响正在研究中。激光束垂直入射到圆柱形散射介质的顶部平坦表面。散射中心是随机分布在介质中的均匀球形颗粒。基于斯托克斯参数的三维矢量输运方程，正在建立一个理论模型。通常的散射相函数将被一个4x4的相位矩阵所取代。利用双重傅立叶变换将输运方程简化为一维形式，并用安巴苏米亚方法求解。然后将使用双重逆傅立叶变换来计算后向散射辐射。首先对球形小粒子进行理论分析，即瑞利散射。为了验证理论模型，将对悬浮在纯水中的乳胶微球进行一系列严格控制的实验。微球的浓度将改变，从而散射介质的光学厚度将从薄到厚不等。这项研究的结果将为一些涉及偏振激光光束与散射介质相互作用的实际问题提供深入的见解。更逼真的辐射模型的发展应该会对激光应用的许多领域产生重大影响，包括传热学、制造业和医学。

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.