基于增益负反馈的COIL自脉冲方法

针对超音速化学氧碘激光器增益介质的横流特性,设计了具有增益负反馈的光学谐振腔结构,通过化学反应的超音速流场和光场的耦合仿真,根据具体的激光器运行参数,论证了这种结构实现自脉冲激光的可行性。结果表明：振荡激光在增益区上游放大次数越多,对上游增益介质能量提取能力越强,脉冲调制作用越显著。采用激光光斑缩束再放大的结构设计,脉冲激光的峰值功率提高10~20倍,从理论上证明了增益负反馈的调制方法能够实现横流激光器脉冲激光输出。     

脉冲CO2激光器峰值功率的增益饱和现象

从理论和实验的角度分析了在腔损耗调制状态下,当调制速度与ＣＯ２激光转动能级间的驰豫速度相当时,激光器输出脉冲峰值功率与增益系数间存在的非线性特性：峰值功率随增益系数的增加,存在饱和现象。这种特性是ＣＯ２Ｂ类激光器的特点,实验和理论模拟结果一致。     

COIL基于小信号增益系数的最佳流量配比选择

 氧碘化学激光器(COIL)的混合喷管内发生的是气体动力学、化学反应动力学以及光学等相互耦合的复杂过程,每个过程都对COIL性能有着至关重要的影响。利用3维CFD技术,通过求解层流Navier-Stokes方程与组分输运方程,结合10种组分和21个基元反应的化学反应模型,对简化后的化学氧碘激光RADICL模型在亚声速段横向射流情况下,不同的主副流流量配比对小信号增益系数的影响情况进行了比较与分析。结果证明:过高或过低的碘分子浓度均不利于产生合理的小信号增益系数;存在最佳流量配比使小信号增益系数得到显著提高且分布均匀。     

氧碘化学激光器增益谱线的实验研究

利用可调谐二极管激光器为探测光源, 直接测量了氧碘化学激光器的增益谱线的精细结构及其各谱线所占比例。同时用碘原子吸收池标定了六条谱线。     

氧碘化学激光器增益谱线的实验研究

 利用可调谐二极管激光器为探测光源, 直接测量了氧碘化学激光器的增益谱线的精细结构及其各谱线所占比例。同时用碘原子吸收池标定了六条谱线。     

连续波氧碘化学激光器小信号增益的测量

描述了利用脉冲光解碘原子激光器作为探测激光器测量连续波氧碘化学激光器小信号增益的方法与装置,给出了增益的测量结果,对实验结果和误差作了简单讨论。     

用吸收光谱法测量COIL的水汽含量

 分析了利用吸收光谱法测量氧碘化学激光器的水汽含量的原理,在氯气流量为0.1 mol/s的N₂-COIL上进行了测试实验。实验结果显示,在常规工作条件下,由于BHP温度变化所引起的水汽百分含量变化仅为0.1%,可以忽略;水汽含量随稀释气体流量增大而增加,气体流速是引起水汽含量变化的主要原因,实验中应把氯气和氧气的比例控制在4∶1之内。     

用吸收光谱法测量COIL的水汽含量

分析了利用吸收光谱法测量氧碘化学激光器的水汽含量的原理,在氯气流量为0.1 mol/s的N2-COIL上进行了测试实验。实验结果显示,在常规工作条件下,由于BHP温度变化所引起的水汽百分含量变化仅为0.1%,可以忽略;水汽含量随稀释气体流量增大而增加,气体流速是引起水汽含量变化的主要原因,实验中应把氯气和氧气的比例控制在4∶1之内。     

COIL简化模型计算

采用简化动力学、增益模型,分析了常规虚共焦非稳腔和含屋脊镜折叠非稳腔这两种腔型在COIL中的应用,计算表明,折叠腔在改善COIL近场光强分布均匀性和提高近场输出功率方面明显优于常规腔。     

化学氧碘激光器高压操作的可行性以及最佳增益区的确定

利用一简单的模型,从理论上证明了在化学氧碘激光器小信号增益存在依赖于系统总氧压力的最佳值,同时讨论了高压下工作的化学氧碘激光器的可行性,最后给出了确定化学氧碘激光器的最佳增益区的方法。     

Fast self-pulsing through nonlinear incoherent feedback

We consider a double-pass ring cavity with nonlinear incoherent optical feedback and analyze its response when it is driven by a continuous laser beam. This particular cavity is equivalent, in the temporal domain, to a simple spatial-pattern-generating system made from a Kerr slice and a feedback mirror. After formulating the evolution equations, we investigate the behavior of small-amplitude solutions and obtain an expression for the round-trip gains. We then explore the important effect of dispersion in the nonlinear medium. Finally, we show that stable modes are possible by solving numerically the full nonlinear equations.     

Onset of instabilities in self-pulsing semiconductor lasers with delayed feedback

We consider the deterministic dynamics of a semiconductor laser with saturable absorber that is subject to delayed optical feedback. Alone, both the saturable absorber and delayed feedback cause the CW output to become unstable to periodic output via Hopf bifurcations. We examine the combined effects of these two destabilizing mechanisms to determine new conditions for the Hopf bifurcations. We also describe the transient as the unstable CW output evolves to the oscillatory state. A main result is that the presence of a saturable absorber can increase the sensitivity of the laser to delayed feedback. Received 1st August 2001 and Received in final form 28 November 2001     

Suppression of self-pulsing in Tm:YAlO3 lasers via current feedback

Self-pulsing of continuous-wave Tm:YAlO₃ lasers limits their use for a variety of important applications. We demonstrate for the first time that the pulsing can be suppressed via feedback to the pump diode laser, a technique that is suitable for both external resonator and monolithic lasers. We also show that the optical transfer function of the laser is that of an unstable relaxation oscillator.     

A 795 nm gain coupled distributed feedback semiconductor laser based on tilted waveguides

The 795 nm distributed feedback lasers have great application in pumping the Rb D1 transition. In this paper, in order to realize specific 795 nm lasing, we designed tilted ridge distributed feedback lasers based on purely gain coupled effect induced by periodic current injection windows through changing the angle of the tilted ridge. The fabricated devices were cleaved into 2 mm-cavity-length, including 5 tilted angles. The peak output powers of all devices were above 30 m W.Single longitudinal mode lasing was realized in all tilted Fabry–Perot cavities using periodic current injection windows,with side mode suppression ratio over 30 d B. The total wavelength range covered 8.656 nm at 20℃. It was disclosed theoretically and experimentally that the output powers, threshold currents, and central wavelengths of the tilted ridge purely gain coupled DFB lasers were relevant to the tilted angles. The results will be instructive for future design of DFB laser arrays with different central wavelengths.     

Adaptive tuning of feedback gain in time-delayed feedback control

We demonstrate that time-delayed feedback control can be improved by adaptively tuning the feedback gain. This adaptive controller is applied to the stabilization of an unstable fixed point and an unstable periodic orbit embedded in a chaotic attractor. The adaptation algorithm is constructed using the speed-gradient method of control theory. Our computer simulations show that the adaptation algorithm can find an appropriate value of the feedback gain for single and multiple delays. Furthermore, we show that our method is robust to noise and different initial conditions.     

基于光电负反馈的激光混沌串联同步系统研究

提出了一种新的混沌中继系统，该系统基于光电负反馈的激光混沌串联同步.对该系统的同步性以及激光器内部参数失配对其同步性的影响进行了研究，并与基于光反馈的激光混沌串联同步系统进行了比较.研究结果表明：当系统参量满足一定条件时，该系统能实现完全同步；当激光器内部参数失配时，其混沌同步性会受到一定的影响，但该系统的混沌同步性对参数失配的容忍性要比基于光反馈的系统好得多.     

基于射频功率调节的负离子源束流反馈控制研究北大核心CSCD

基于射频负离子源的中性束注入系统是高功率长脉冲(稳态)运行中性束注入系统的最佳选择。负离子源是中性束注入系统的核心部件,需要实现稳定的负离子束引出和加速。在负离子源的运行过程中引出负离子电流会发生变化,尤其在长脉冲、高能量运行条件下会更加明显,因此无法满足稳定运行的要求。为了实现引出束流的稳定引出,开展了束流反馈控制研究,研发了一套基于射频功率调节的束流反馈控制系统,并将束流反馈控制系统应用在射频负离子源测试平台,开展了束流反馈控制测试。测试结果表明束流反馈控制系统能够实现对束流的实时反馈调节以获得束流的稳定引出,验证了基于射频功率调节的束流反馈控制的可行性,为高功率射频负离子源的研制提供支持。     

分布反馈式光纤激光器的光热调谐方法

针对现有光纤激光器调谐方法通常不能兼顾调谐幅度和调谐速率的问题,提出了一种基于光热效应的调谐方法,有效兼顾了调谐幅度和调谐速率的要求。分析了光纤激光器的输出波长随泵浦功率变化而改变的实验现象,并以980 nm泵浦源自身调谐为例,进行了静态和动态实验,结果表明:基于光热效应的分布反馈式光纤激光器静态调谐幅度达392 MHz/100 mA,动态调谐速率超过2 kHz,验证了光纤激光器光热调谐方案的可行性。