二维随机介质中偏振模式的竞争和阈值特性

基于随机激光的时域理论,建立了横磁与横电光波模式共享反转粒子数情况下的理论模型,并利用时域有限差分法(FDTD)数值求解麦克斯韦方程组和速率方程组,从而获得了二维随机介质内横磁与横电光波模式的阈值特性.结果表明,如果横磁与横电偏振模式之间没有共享反转粒子数,则横磁光波模式拥有较低的激发阈值;反之,则横电光波模式的激发阈值更低.在共享反转粒子数的情况下,改变样品的表面填充率对两种偏振模式的阈值并没有很大的影响,而增加样品面积则可以明显的降低横磁模式的阈值.     

二维随机激光器的模式选择及阈值与饱和特性

基于将Maxwell方程与四能级原子系统速率方程相结合而建立起随机激光时域理论，并利用有限时域差分法，研究了二维随机介质中激光模式的输出特性与介质尺寸、外形及抽运速率等参数的关系.结果表明，与传统激光模式相似，随机激光模式的强度随抽运速率的变化不仅具有阈值特性，而且具有饱和特性.基于模式特性对介质及抽运参数的依赖关系，提出了二维随机激光器的选模方式，在很大程度上不同于传统激光器的选模方式. 关键词： 随机激光器 模式选择 无序介质中的光学特性     

宽谱染料激光器的数值模型及实验验证

应用染料激光器半经典理论,数值模拟了脉冲染料激光器双频及宽谱共增益区的谱线竞争效应,与实验结果符合较好.在双频相关调谐工作条件下,调谐范围增大近25％.在宽谱工作条件下,随着输出耦合损耗增大,谱线宽度逐渐减小. 关键词： 染料激光器 半经典理论 谱线竞争     

掺杂铌酸锂He—Ne相位共轭激光器的稳态输出特性

实验研究了以Ce:Fe:LiNbO_3晶体为相位共轭镜的He-Ne外泵浦相位共轭激光器的稳态输出特性.并建立了在强泵浦条件下的理论公式.理论与实验曲线在趋势上相一致.     

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.     

光注入掺铒光纤激光器的混沌特性

对光注入情况下混沌光纤激光器的输出特性进行实验研究.混沌光纤激光器采用环形腔结构,利用光纤的非线性克尔效应产生混沌激光.主激光器产生的混沌激光通过光隔离器和光纤耦合器注入到混沌掺铒光纤激光器实现外光注入.将主激光器产生的不同功率的混沌信号注入从激光器,研究光注入后从激光器混沌信号时序、频谱、自相关以及稳定性与复杂度等特性.结果 表明,光注入后的混沌信号时序随机且幅度频数呈高斯分布,频谱无明显的周期特性,自相关特性优良.光注入掺铒光纤激光器混沌输出在保证混沌源高复杂度的同时提高了混沌源的稳定性.     

光纤光栅对的参数匹配与激光输出特性

高功率光纤激光器的激光输出特性优化,对进一步提高光纤激光器的输出功率以及实际应用中的切割、加工质量具有重要意义.斜率效率、背向漏光以及受激拉曼散射是高功率光纤激光器设计中较为关心的输出特性参数.作为核心器件,光纤光栅对的参数设计与匹配,会直接影响到整个激光系统的性能.本文旨在探究光纤光栅对的参数匹配对激光输出特性的影响,先是通过理论分析分别阐述了斜率效率、背向漏光以及受激拉曼散射的来源与相互关系;然后通过实验设计,采取了两组不同参数光纤光栅对组合,从实验上分别探究了低反光纤光栅的光谱带宽以及反射率对激光输出特性的影响.最后得出了光纤光栅对的优化参数与匹配原则,为提高连续光纤激光器的激光输出特性提供了理论支持与参考价值.     

自调Q光纤激光器的理论分析和数值模拟

基于自调Q光纤激光器的基本理论,结合速率方程理论与自调Q特点,借助简化的环形腔掺Er3+光纤激光器模型,分析了泵浦功率与自调Q脉冲周期、峰值功率的关系.随着泵浦功率的增加,光纤激光器自调Q脉冲的周期减小,峰值功率变大；当信号光强足够大时,激光器的自调Q现象消失,变为准连续激光输出.通过MATLAB编程对光纤激光器输出特性进行了数值模拟,模拟结果与实验结果基本相符.     

高能掺镱离子光纤激光器的研究

从激光器的速率方程出发,对光纤激光器的工作原理以及输出特性进行了研究,得到了光纤激光器在稳态条件下阈值条件和激光器输出功率的表达式.利用数值模拟结果对光纤激光器基本参量进行分析和论证.为光纤激光器的优化设计提供理论依据.并提出了全光纤型光纤激光器的实验方法.获得了最大功率7.5 W、波长1080 nm、峰值半宽0.11 nm的连续单模激光输出.     

同轴谐振腔高阶横磁模式参数的研究

理论计算和分析了微波圆柱同轴谐振腔高阶横磁(TM)模式的系列关联参数.研究发现：与圆柱腔相比, 同轴谐振腔的TM_n10模式有较大的模式间隔，即工作模式能够远离非工作模式的干扰，这有利于保持器件稳定的频率和功率；在保持腔长不变、腔横截面外半径取特定值时，腔内电场峰值位置的轴向特性阻抗随内径的变化存在极大值；在高频段可以采用任意大横截面的腔体结构和任意阶的模式.计算结果与仿真结果相一致. 关键词： 高阶横磁模式 圆柱同轴谐振腔 特性阻抗 多注速调管     

Lasing modes in a spiral-shaped dielectric microcavity

The resonance patterns and lasing modes in a spiral-shaped dielectric microcavity are investigated through passive and active medium calculations. We find that the high-Q resonance modes are whispering-gallery-like modes, and these resonance modes can be easily excited as lasing modes. We also find that the quasi-scarred resonance mode, which shows strong directional emission beams from the cavity boundary, can be excited with selectively applied external pumping. Through a spectral analysis of the time evolution of the light field, the competition between these lasing modes is discussed.     

Lasing with guided modes in ZnO nanorods and nanowires

A vertically arranged nearly parallel array of ZnO nanorods and randomly oriented nanowires has been grown by low pressure chemical vapor deposition (CVD) on silica substrates and on stainless steel gauze woven from a wire with a diameter of 40 μm, respectively. The quality of the produced material is high enough to act as a gain medium for stimulated emission in the ultraviolet spectral region. Multiple sharp lasing peaks were realized from single hexagonal nanorods and arrays of hexagonal ZnO nanorods. The lasing peaks display successive onset and saturation with increasing excitation power density and fit well the expected resonance spectrum of guided modes in hexagonal nanorods. The behavior of lasing spectra from shot to shot of pumping in randomly oriented nanowires along with the independence of the lasing threshold on the excitation spot area suggest that the emission spectrum results from the superposition of lasing modes in individual nanowires, rather than from random lasing due to photon coherent scattering.     

Dynamic nonlinear effect on lasing in a random medium

We have studied both experimentally and numerically the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes the frequency and size of lasing modes, but also modifies the laser emission intensity and laser pulse width. When the nonlinear response time is longer than the lifetime of the lasing mode, the nonlinearity changes the laser output through modifying the size of the lasing mode. When the nonlinear response is faster than the buildup of the lasing mode, positive nonlinearity always extracts more laser emission from the random medium due to the enhancement of single particle scattering.     

Statistics of random lasing modes in weakly scattering systems

We investigated the statistics of random lasing modes in colloidal solutions with local pumping. The ensemble-averaged spectral correlation function of single-shot emission spectra exhibits regular oscillations. The statistical distribution of laser emission intensity follows a power-law decay, in comparison with an exponential decay of the statistical distribution of amplified spontaneous emission (ASE) intensity. The dramatic difference between the statistics of lasing peaks and that of the stochastic ASE spikes illustrates their distinct mechanisms.     

Characterization of the 46.9-nm soft X-ray laser beam from a capillary discharge

Intense lasing had been obtained from argon plasma in the soft X-ray region from a capillary discharge plasma system. Different diagnostics have been used to characterize the lasing properties by recording the temporal, spatial, and spectral profiles of the emission. The divergence measurement indicates that the soft X-ray laser beam has good directionality with a divergence of 3.5 mrad. The spectrum of the laser beam measured using a transmission grating showed intense lasing line at 46.9 nm. Diffraction orders as high as 10th orders were observed. The temporal profile recorded with a vacuum diode showed a distinct laser peak with a pulse width ~1.2 ns (FWHM). In addition, the coherence of the X-ray laser beam was also confirmed from the high-contrast interference fringes (visibility ~85 %) recorded using double slits.     

Intense directional lasing from a deformed square-shaped organic-inorganic hybrid glass microring cavity

Intense directional light emission from a deformed square-shaped organic light-emitting microring cavity was observed. The ring cavity was a dye-doped organic-inorganic hybrid glass film coated upon a square-shaped fiber. From the near-field and far-field emission patterns and their emission spectra we found, for the first time to our knowledge, the simultaneous existence of chaotic whispering-gallery modes and four-bounce reflection modes. The two types of mode have different emission directions, different lasing thresholds, and different spectral linewidths. High-contrast angle-modulated light emission was also observed. We could control modulation and angular spread of emission by controlling the deformation of the cavity.     

Cavity-Q-driven phenomena in an evanescent-wave pumped and gain coupled whispering-gallery-mode fiber laser

We study cavity-Q-driven lasing wavelength shift and line-width widening in an evanescent-wave pumped and gain coupled Whispering-Gallery-Mode (WGM) fiber lasers. A bare optical fiber is immersed in a lower refractive index (RI) dye solution, pumped and gain coupled by evanescence waves, and linearly polarized WGM lasing emission is observed from the rim of the fiber. We find that both lasing wavelengths and line width of WGM peaks are sensitive to the RI of the dye solution and the fiber diameter, with the increase of the RI of the dye solution or decrease of the fiber diameter, a blue shift of the lasing spectrum and a widening on the spectral line width are observed. The observed phenomena have been attributed to the change of quality factor of a circular cavity built in the fiber cross section, the achieved experimental data agree well with the calculated values of the quality factor.     

柱形微腔回音壁激光光谱模式的精确标定

由柱形微腔中回音壁模式满足的本征值方程,得到确定回音壁模式位置和间距的近似解析公式。以此近似解析公式,首次对直径在215～328 μm间的5个柱形微腔回音壁激光光谱做了模式标定。在用近似解析公式对柱形微腔激光光谱的数值作拟合的计算中,除了回音壁模的径向模式数(l)和角动量模式数(n)外无需其他拟合参数,解析公式的拟合值和实验激光光谱波长值间的偏差小于0.05 nm,拟合结果精确可靠。柱形微腔回音壁激光光谱模式的精确标定在模式的场分布计算以及频移型微腔生物传感器的研究应用中具有重要作用,文章介绍的方法亦可应用于柱形微腔直径和折射率的精密测量。     

Mode beating in spot-size converter lasers

An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper.