光在随机增益介质中的放大

 结合环形腔理论，运用蒙特卡罗法模拟了光子在介质中的随机行走。研究了倍频Nd:YAG（脉宽6 ns，频率20 Hz）脉冲激光器作为泵浦光，在TiO₂ / 若丹明 B有机增益介质中，散射微粒的颗粒密度和泵浦光面积对随机激光器阈值强度的影响。模拟结果表明：随机激光阈值和光子在增益介质中的随机行走路程长度和光子通过边界返回增益区和非增益区的几率有关。随着泵浦光面积的增加，随机激光器阈值降低；增益介质中散射颗粒密度的增加降低了随机激光器的阈值。     

掺铒光纤环形激光器输出特性的研究

根据掺铒光纤激光器的速率方程，对环形腔光纤激光器的输出特性进行了理论分析，得到了光纤激光器在稳态条件下阈值抽运功率、激光输出功率和斜率效率的解析表达式。利用数值模拟结果对光纤激光器的这些基本特性参量进行了分析和讨论，为光纤环形激光器的优化设计提供了依据。并进行了980nm抽运的掺铒光纤激光器的实验，实验证明理论分析得到的基本特性是合理的。     

一种控制环形激光器光学腔长的新方法

提出了一种控制环形激光器光学腔长的新方法.该方法是利用压电陶瓷电控环形激光器毛细管内干燥空气的折射率，实现对环形激光器光学腔长的控制.这种控制方法对环形激光器性能影响很小，具有响应速度快、灵敏度高、功耗低等优点，可用于全反射棱镜式环形激光器、反射镜式环形激光器的稳频系统.对于激光陀螺、激光计量等应用具有重要意义.     

环形激光器反射镜相位延迟差测量方法研究

理论上推导出了环形激光器对Ｓ光和Ｐ光相位延迟差与其拍频峰对应的压电陶瓷电压差的关系式,分析了方形环形激光器对Ｓ光和Ｐ 光的频率响应特性,通过测量拍频峰电压差实现环形激光器反射镜相位延迟差测量。通过搭建环形激光器频率响应特性测试系统,从实验上验证了理论计算的正确性。结果表明,该方法测量误差小于１．５％,满足环形激光器反射镜相位延迟差测量要求。     

波导随机散射系统的激光发射

提出在随机分布的散射微粒中嵌入环形波导结构以改善随机激光器的随机发射特性。利用时域有限差分法(FDTD),数值模拟了内嵌环形波导的随机散射系统及其对比结构中光场的分布,得到了各结构的模式频谱。结果显示,本结构只在中心处有激光出射,表明环形波导的存在可以影响随机系统的激光发射,减少激光的模式输出,并在一定程度上增强了出射激光的强度。     

环形激光器用于角速度测量的实验

基于环形激光器测量角速度的原理,搭建了实验系统,测量了环形激光器频差与步进电机转动角速度的关系.实验表明环形激光器可用来进行角速度的测量.     

轻微非共面腔的输出片应力作用研究

 建立了计算轻微非共面腔输出光椭圆度的数学模型,分析了R. H. Moore专利中的理论计算错误,计算分析了输出片的应力作用对输出光椭圆度的影响,发现：输出镜片的应力作用对环形激光器顺时针方向和逆时针方向输出光椭圆度的非对称有影响。通过实验验证了理论计算的正确性。得出R. H. Moore, S. W. Hammons等人在专利中提出的调腔方法存在错误,它不能有效地消除环形激光器中由腔体轻微异面所引起的磁效应。     

环形光纤激光器中的半导体光波导调制器

对环形光纤激光器中的半导体光波导调制器进行了理论研究，结果表明，光纤环中的偏振控制器对光的偏振态的控制以及半导体光皮导对光的偏振态的调节构成了激光器的主要调制机理，为环形光纤激光器的自调Ｑ及锁模的新机制提供了理论依据。     

光纤环形腔激光器输出特性的研究

对由不同长度的掺饵光纤、不同分光比的耦合器构成的光纤环形腔激光器的输出特性进行了实验研究。通过理论与实验分析,得出了激光器的输出功率、斜率效率与掺铒光纤的长度、耦合器的分光比有关,而且存在最佳值的结论。     

全反射棱镜式环形激光器耦合输出的理论分析

对采用棱镜耦合器的全反射棱镜式环形激光器的耦合输出特性进行了理论研究, 导出了有“楔形”间隙的棱镜耦合器的反射系数和透射系数表达式, 给出了反射率和透过率随“楔形”间隙高度变化的理论计算曲线, 进而研究了有关材料选取、腔内振荡分量的选取及减小棱镜耦合器对环形激光腔内模式的影响等问题. 这些研究对于全反射棱镜式环形激光器在激光陀螺、激光角速度传感器等实际应用中有重要意义.     

Statistical properties of single-mode and two-mode ring lasers

Recent theoretical and experimental investigations of the statistical properties of single-mode and two-mode ring lasers are described. A theory of the frequency dependence of laser light fluctuations in a single-mode laser and the photoelectric experiments testing the predictions of this theory are discussed. For the case of two-mode ring lasers, a theoretical discussion of the steady-state and transient properties, such as photon statistics, first-passage-time distributions, correlations and phase locking, is given. Theoretical predictions are compared with the results of photoelectric measurements carried out on two-mode gas and dye ring lasers. A summary and the principal conclusions of this article are presented, and suggestions for further investigations are made.     

Lasing in random media

A random laser is a non-conventional laser whose feedback mechanism is based on disorder-induced light scattering. Depending on whether the feedback supplied by scattering is intensity feedback or amplitude feedback, random lasers are classified into two categories: random lasers with incoherent feedback and random lasers with coherent feedback. A brief survey of random lasers with incoherent feedback is presented. It is followed by a review of our recent experimental work on random lasers with coherent feedback, including measurement of the lasing threshold, lasing spectra, emission pattern, dynamical response, photon statistics, speckle pattern and the investigation of relevant length scales. Large disorder leads to spatial confinement of the lasing modes, that is the foundation for the micro random laser. Some theoretical models of random lasers with coherent feedback are briefly introduced. The study of random lasers improves our understanding of the interplay between light localization and coherent amplification.     

Nanolasers Enabled by Metallic Nanoparticles: From Spasers to Random Lasers

Owing to exotic optical responses, metallic nanoparticles and nanostructures are finding broad applications in laser science, leading to numerous design variations of plasmonic nanolasers. Nowadays, two of the most intriguing plasmonic nanolasing devices are spasers and random lasers. While a spaser is based on a single metallic nanoparticle resonator with the optical feedback provided by the localized surface plasmon resonance, the operation of a random laser relies on multiple light scattering within randomly distributed metallic nanoparticles. In this paper, an up‐to‐date review on the applications of metallic nanoparticles in spasers and random lasers is provided. Principles of a random spaser, a device combining the features of a spaser and a random laser, are briefly discussed as well. The paper is focused on major theoretical and experimental approaches to control the core metrics of lasing performance, including threshold, resonant wavelength, and emission directionality. The applications of spasers and random lasers in the fields of sensing and imaging are also mentioned. Finally, the challenges and future perspectives in this area of research are discussed.     

Random distributed feedback fibre lasers

The concept of random lasers exploiting multiple scattering of photons in an amplifying disordered medium in order to generate coherent light without a traditional laser resonator has attracted a great deal of attention in recent years. This research area lies at the interface of the fundamental theory of disordered systems and laser science. The idea was originally proposed in the context of astrophysics in the 1960s by V.S. Letokhov, who studied scattering with “negative absorption” of the interstellar molecular clouds. Research on random lasers has since developed into a mature experimental and theoretical field. A simple design of such lasers would be promising for potential applications. However, in traditional random lasers the properties of the output radiation are typically characterized by complex features in the spatial, spectral and time domains, making them less attractive than standard laser systems in terms of practical applications. Recently, an interesting and novel type of one-dimensional random laser that operates in a conventional telecommunication fibre without any pre-designed resonator mirrors–random distributed feedback fibre laser–was demonstrated. The positive feedback required for laser generation in random fibre lasers is provided by the Rayleigh scattering from the inhomogeneities of the refractive index that are naturally present in silica glass. In the proposed laser concept, the randomly backscattered light is amplified through the Raman effect, providing distributed gain over distances up to 100 km. Although an effective reflection due to the Rayleigh scattering is extremely small (∼0.1%), the lasing threshold may be exceeded when a sufficiently large distributed Raman gain is provided. Such a random distributed feedback fibre laser has a number of interesting and attractive features. The fibre waveguide geometry provides transverse confinement, and effectively one-dimensional random distributed feedback leads to the generation of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres).     

双光子抽运随机激光器中辐射光能量的演化

基于非相干反馈随机激光器的扩散方程理论，将扩散方程中的增益项改写为饱和形式，并利用有限差分方法，研究了双光子抽运随机激光器中辐射光能量随时间演化特性.对扩散方程的数值求解给出了系统辐射光能量由自发辐射开始，经历小信号增益状态得到放大，再到由于增益饱和形成稳态输出的整个演化过程.表明介质的无序导致了在较低能量情况下也能获得饱和增益这样的非线性效应.结果为研究获得双光子抽运随机激光器的稳态输出提供了理论依据. 关键词： 随机激光器 双光子抽运 饱和效应 无序介质中的光学效应     

固体激光器光束合成特性分析

光束合成是研制高功率、高光束质量固体激光器的必由途径.建立板条介质固体激光器阵列光束合成的理论模型,从子束间距、整体相位差、偏振态、随机像差等方面,分析了合成光束的远场特性.通过数值模拟可以看到,子束间距决定了合成光束远场光斑的衍射旁瓣的大小和多少;子束间整体相位差决定着合成光束远场中心光斑是否分离,并影响着峰值光强和...     

粉末随机激光辐射

粉末随机激光辐射是一种刚刚被人们发现的激光过程,这种激光由粉末状介质的多次散射来提供光学反馈,不需要外加谐振腔。随机激光辐射过程除了对激光物理有很大意义之外,还有巨大的应用前景,例如,有可能在平板场发射显示器中得到广泛应用,文章介绍了粉末激光的原理及其实现过程。     

Chirped and chirp-free femtosecond pulses in passively mode-locked dye lasers

Femtosecond light pulse generation in a ring laser and its propagation properties are described. The basic principles and some theoretical aspects of the pulse generation process in dye lasers are summarized taking into account the influence of the amplifier, of the saturable absorber, of the glass path and of mirrors. Phase modulation arising from multilayer dielectric mirrors has been calculated and measured by determination of an equivalent intracavity glass path length. The main source of phase modulation (chirp) seems to be the saturable absorber.     

Multi-state optical flip-flop memory based on ring lasers coupled through the same gain medium

We investigate a system consisting of multiple ring lasers coupled by a single gain medium. All the ring lasers share a common feedback arm. The output power of an individual laser shows periodic oscillations as a function of time. The periodicity of the oscillation is determined by the ratio of the roundtrip times of the feedback arm and the ring cavity. In the case that two of such ring lasers are coupled, either their oscillation periodicities are synchronized, or the system is bi-stable. In the latter operation regime, the system can act as an optical flip-flop memory whose state be switched by injection of external light. The concept can be extended to multi-state operations; an eight-state optical flip-flop memory is experimentally demonstrated.     

Experimental characterization of nonlinear harmonic generation in planar and helical undulators

We present an experimental characterization of the process of coherent harmonic generation in single-pass free electron lasers. The harmonic radiation is obtained by seeding the electron beam stored in the Elettra storage ring with a Ti:sapphire laser. Different methods for generating harmonics are compared between them, and a detailed characterization of the emitted light is performed for different polarizations. Our results also contribute to the debate about the possible presence of a coherent on-axis signal in helical undulators. In this respect, we provide an experimental confirmation of recent theoretical studies that predict no coherent on-axis signal.