板条激光放大器中寄生振荡的研究

寄生振荡的存在使得放大器在信号光到达之前消耗了大量的反转粒子数,降低了放大器的激光增益和储能效率,严重地影响了激光放大器的性能,尤其对高功率激光放大器。在理论分析和实验研究的基础上,以Nd∶YAG晶体板条为例,用8条半导体激光阵列对晶体进行双侧抽运,研究了高功率激光放大器的寄生振荡现象,分析了板条晶体寄生振荡产生的原因,并详细比较了晶体在不同的抽运功率和表面处理下的放大效果,得到了2倍的单程放大,当输入能量为140 mJ时,获得了278 mJ的激光输出。     

二极管侧泵浦单横模1kHz电光Q开关激光器

 本文介绍了二极管侧泵浦Nd:YAG板条1kHz重复频率Q开关激光器的研制,实验获得最大单脉冲能量0.712mJ,脉宽小于10ns的输出。对Nd:YAG板条进行了三种冷却方式的比较实验,实验证明DPL在高重复频率工作时,激光介质的热效应是影响高重复频率工作的激光器效率的重要因素。     

掺铒光纤放大器中抽运问题的理论分析

依据掺铒光纤放大器的速率方程和光传输方程,在不计放大自发辐射的情况下,得出了抽运功率和信号增益在放大器中沿光纤分布的隐函形式的解析表达式,并利用数值模拟对三种抽运方式下的放大器特性进行了分析。     

纵向泵浦固体激光介质热透镜效应的理论研究

 在分析了纵向泵浦、周边致冷固体激光棒内加热及冷却机理的基础上,将热传导方程合理简化为一维形式,求解出以级数方式表达的棒内温度分布。并根据热弹性力学原理,获得了激光棒中热致应力场和应变场。在考虑了与热透镜效应有关的三个因素：即热色散、热致应力双折射和端面变形后,推导出了纵向泵浦固体激光棒有效热焦距的解析表达式。将所获结果运用于常用的激光晶体Nd:YAG,发现当使用10W半导体激光器泵浦时,所产生的有效热焦距在毫米量级。     

Theoretical and numerical study of Couette-Taylor flow with an axial flow using lattice Boltzmann method

In this study, the numerical models for swirling flows developed by Li et al and Zhou for lattice Boltzmann method (LBM) are chosen. These models were firstly validated using the Couette-Taylor flow between two concentric cylinders simulations. Numerical results showed the efficiency of the Zhou's model. Numerical simulation results using LBM are in good agreement for the steady and unsteady regimes compared to the literature review. In a second step, the Zhou model was then adopted to our study to determine the Couette-Taylor instabilities with an axial flow. Two protocols are tested. The first one (direct protocol) starts with an azimuthal flow without any axial flow (Re = 0). Once the regime is established, an axial flow is then superposed to the Couette-Taylor flow (with a sudden or a progressive manner). The second protocol (inverse protocol) starts with an axial flow at a given Reynolds number (Poiseuille flow). Once the regime is established, an azimuthal flow is the executed (with a sudden or a progressive manner). The effect of various parameters controlling the physical situation is also discussed. The increase of the azimuthal velocity mainly led to the emergence and development of Taylor vortices. Its influence decreases when the axial Reynolds number increases. The relevant result for this study is the change of the critical axial Reynolds number Re_c (total disappearance of instabilities) with both protocols and both manners.     

激光加工微凹坑轴表面对唇形密封泵吸及摩擦特性的影响

为了研究轴表面形貌对径向唇形密封泵吸作用及摩擦特性的影响,利用Nd:YAG固体脉冲激光对旋转轴表面进行微凹坑织构化处理,在油封密封试验机上,针对不同转速、不同表面形貌等工况,完成了一系列对比试验,获取了试验过程中的泵吸量、摩擦力以及密封圈温升等参数.并通过扫描电镜对试验后各密封唇表面进行了分析.结果表明:三角形微凹坑顶点朝向油液侧的表面能够增强泵吸作用,且转速对泵吸率影响很大,而其他形状和参数的微凹坑表面不利于泵吸作用的产生;与未织构面相比,圆形凹坑面积占有率为7%和21%的表面具有良好的减摩效果,三角形凹坑顶点沿周向的两表面间减摩效果较好.     

Investigation of magneto-optical effect in transverse magnetic field in He

The non-linear Voigt effect has been studied in He discharge under resonance laser interaction with the He transition. The range of non-linear signal existence was determined. The contribution of the lower and upper states to the overall signal was analyzed. The cross-section for depolarizing collisions with ground state He atoms was estimated for the 3³ D _2,3 He state. Received: 16 June 1998 / Received in final form: 14 December 1998     

氢分子振动态与铯分子基态碰撞中转动-振动能量转移

利用受激拉曼泵浦将H2激发到v=1，J=3态，研究了H2(1, 3)态与Cs2分子碰撞(1, 3)态的弛豫及Cs2(X1+g)振动态的激发过程。利用相干反斯托克斯拉曼散射(CARS)检测H2的振转态分布，由CARS峰值得到密度比[H2(1, 3)]/[H2(0, 3)]和[H2(1, 1)]/[H2(1, 3)]，由H2(v=0)振转态的Boltzmann分布确定H2(0, 3)的密度，由此得到[H2(1, 3)]和[H2(1, 1)]态的密度。激光诱导荧光光谱(LIF)确定被碰撞激发的Cs2(X1+g, v=11-15)各态。利用单模半导体激光作瞬时光吸收，对于v= 11, 12, 13, 14和15，积分吸收系数(单位：106cm-1s-1)分别是6.5，7.9，7.0，6.1和4.7，结合H2(1, 3)的密度，得到H2(1, 3)Cs2(X1+g, v)的转移速率系数，对于v=11-15，分别是(单位：10-13cm-1s-1)1. 40. 6，1.70. 7，1.50. 6，1.30.5和1.00. 4。利用吸收线Doppler增宽测量分别得到了Cs2(X1+g, v=11-15)的平动能。     

NMR Hyperpolarization Techniques for Biomedicine

Recent developments in NMR hyperpolarization have enabled a wide array of new in vivo molecular imaging modalities, ranging from functional imaging of the lungs to metabolic imaging of cancer. This Concept article explores selected advances in methods for the preparation and use of hyperpolarized contrast agents, many of which are already at or near the phase of their clinical validation in patients.     

Optical bistability via quantum interference from incoherent pumping and spontaneous emission

We theoretically investigate the optical bistability (OB) in a V-type three-level atomic system confined in a unidirectional ring cavity via incoherent pumping field. It is shown that the threshold of optical bistability can be controlled by the rate of an incoherent pumping field and by interference mechanism arising from the spontaneous emission and incoherent pumping field. We demonstrate that the optical bistability converts to optical multi-stability (OM) by the quantum interference mechanism.