激光是20世纪最伟大的发明之一。近年来，激光研究领域出现了重要进展，随机激光器。它不再依靠传统的谐振腔进行反馈，而是利用无序结构中的随机散射提供反馈，从而实现高强度的受激辐射。由高度随机介质中的受激辐射构成的激光器称为随机激光器，它蕴含着丰富的物理现象和物理意义，是当今物理学界的一个研究热点。通常，随机激光器可以分为相干反馈型随机激光器和非相干反馈型随机激光器。这两种反馈类型的随机激光器，既可以在强散射介质中实现，也可以在弱散射介质中实现。在强散射介质中，用光子的安德森局域来解释其发光机制，被大家所接受。但是在弱散射介质中，随机激光器的发光机制和模式特征仍是众说纷纭，有待进一步的深入研究。目前我们课题组在弱散射随机激光领域的研究中取得了一些成果，将在本文中详细描述。在第一章，我们将传统激光器与随机激光器进行比较，揭示出它们的本质区别。从随机激光器的理论猜想，到当今随机激光器的制作，介绍了随机激光器的发展历程和现状。阐述了随机激光器在光集成、激光器制造、光信息识别与处理、生物医药等方面的应用价值。在第二章，我们简单介绍了散射和安德森局域的有关理论，详细阐述了Lawandy和Cao.H课题组的有关实验以及他们给出的相关理论解释。在第三章，我们制作了一个弱散射结构随机激光器，利用罗丹明6G溶液作为增益介质，以532nm的纳秒激光作为泵浦源，用氧化锌纳米颗粒作为随机散射粒子，组成实验系统。研究散射的平均自由程，观察从荧光到相干受激辐射的过程，阈值特性和影响随机激光模式的因素。其中包括一些新现象，这些新现象利用已有的理论不能得到有效的解释，为此我们提出了腔耦合的概念，在理论上能够很好的解释这些新现象。在第四章，我们对纯罗丹明6G溶液进行泵浦时，发现也有激光产生，这种激光产生的机制并不是靠传统谐振腔反馈，也没有随机散射介质，但是却存在着相干反馈机制。我们认为在用泵浦光照射时，增益介质中会存在折射率梯度，形成有效的边界，从而实现相干反馈，这是一种全新的相干反馈机制。通过实验，我们证明了折射率梯度的存在。利用这一现象，我们制作了一些激光系统，得到了一些非常好的特性，对应着广泛的应用前景。

The laser is one of the greatest inventions of the 20th century. In recent years, there are some important progress in the field of laser research—random lasers. It is known that, the positive feedback is the key factor in a lasing system, provided by artificial cavity in traditional laser and random scattering in random laser. It contains a wealth of physical phenomena and physical principles, becomes a hot research point in the physics.Generally, there are two kinds of mechanisms for random lasing: coherent feedback and incoherent feedback. Up to now, coherent random lasers have been achieved in both of the strongly and the weakly scattering systems. The physical picture for lasing in strongly scattering systems is widely accepted. On the other hand, the understanding of coherent random lasers in weakly scattering regimes is still an open question.Our group had discovered some new experimental phenomena and proposed some explanation, which will be described in detail in this article.In chapter 1, we compare traditional laser with random lasing, and point the essential difference. Then, we introduce the development process from theoretical guess to the actual production, and present development situation in this field. We describe the value of random lasers, such as optical integrated, laser manufacturing, optical identification and processing, biomedicine and others.In chapter 2, we introduce the theory of the scattering and Anderson localization in briefly. Then, we describe the physical phenomena and explanations reported by Lawandy and Cao.H respectively.In chapter 3, we set up an experimental system. The sample of the disordered system was the methanol solution containing Rhodamine 6G (R6G) laser dye as the gain material and ZnO nanoparticles as the scatters. The Nd: YAG laser (532nm) was employed as the pump source. We firstly illustrate the measurement of MFP of our disordered structure. Secondly, we observe the process from fluorescence to laser, with increasing the power of pump laser, the character of threshold, and the influencing factors of laser mode. Many new phenomena cannot be explained perfectly with old views. So, finally, we propose a new Concept—cavity coupling，which could explain this new phenomena.In chapter 4, a new kind of mechanism of lasing is investigated experimentally. It is quite different from the traditional laser with cavity and the random laser with random scattering. In this mechanism, the intensity-dependent refractive index effect and thermal nonlinear optical effects of the pump beam induce a large gradient of the refractive index in the gain material, which forms a passive equivalent boundary that provides the feedback in the lasing system. A real lasing system, a liquid disk laser, is performed. The property will be useful in many fields.