Influences of finite gain bandwidth on pulse propagation in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulations with the nonlinear Schr¨odinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing a small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful for the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

Influences of finite gain bandwidth on pulse propagating in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulating with the nonlinear Schrödinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful to the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.     

非单色光抽运的光参量啁啾脉冲放大的带宽及增益特性研究

采用傅里叶变换的方法将脉冲光分解成不同的频率成分,建立了非单色光抽运的光参量放大耦合方程组的数值求解模型.研究了非单色抽运光对光参量啁啾脉冲放大的小信号增益、大信号增益以及增益带宽的影响.非单色抽运光降低参量放大的增益水平,但同时可提高增益带宽,且抽运光谱宽越宽,对增益带宽的提高作用越大.还进一步从相位失配和参量带宽的角度分析了非单色抽运光使参量放大的增益降低、带宽增大的原因. 关键词： 光参量啁啾脉冲放大 非单色光 增益带宽 飞秒激光     

Broadband gain-clamped linear quantum dash optical amplifiers

The linear optical gain of gain-clamped quantum dash semiconductor optical amplifiers (GCSOAs) has been investigated using the rate equation model. The gain spectrum of GCSOA for different wavelength detuning and different doping has been studied. Our analysis shows that the linear gain can be increased as the laser wavelength is detuned to high wavelength where the peak of the optical gain, which is found at wavelengths below the ground state wavelength, is shifted to lower wavelength as the laser wavelength is increased. We find that doping the dashes by either N-type or P-type enhances the linear optical gain and shifts the gain peak to lower wavelength. Moreover, we found that GCSOA with lightly N-type doping demonstrates large separation between the laser and the amplifier wavelength. Also we find that small inhomogeneous line broadening enhances the linear gain peak, shifts the gain peak to wavelength lower than the GS wavelength and widens the gain spectrum.     

激光二极管抽运单/双增益模块的液体激光系统性能对比

单增益模块的无机液体激光体系在通过流动循环散热时,也导致抽运区域的增益介质在流动方向上产生了热梯度.而双增益模块的液体激光系统既能有效地散热,同时也避免了流动方向的热梯度,具有较好的性能.采用数值计算方法模拟了同样增益长度的单、双增益模块系统的热特性和输出激光的远场光斑分布,并进行了对比分析.结果表明双增益模块液体激光系统的性能明显优于单增益模块系统:远场光斑的峰值强度提高一个数量级,能量集中度和光束质量均得到明显的提高.     

周期排列共振放大介质的小信号增益特性研究

研究一维周期排列共振放大介质的小信号增益特性.研究结果表明小信号增益随着作用长度的增加表现出异常的放大特性.在满足严格布拉格共振条件下，介质折射率分布形成的带隙和增益效应之间的相互竞争决定了透射光场的变化.进一步讨论了增益大小与激子参数和共振原子之间的依赖关系. 关键词： 周期共振放大介质 小信号增益 光子带隙     

波荡器位相误差对自由电子激光

 对波荡器位相误差对自由电子激光小信号增益的影响进行了分析讨论。对低增益情况解析地给出了波荡器位相误差引起的增益降低因子。结果表明：与自发辐射类似增益的降低与位相误差的方差成简单的指数关系，位相误差的线性变化部分引起最大增益的位移，还表明波荡器位相误差存在时Madey定理仍然成立。对高增益情况也给出了波荡器位相误差引起的增益降低因子。     

高功率梯度掺杂增益光纤温度特性理论研究

在高功率光纤激光器中, 增益光纤的热效应是限制激光功率进一步提高的重要因素之一. 为了降低增益光纤的最高温度, 提出了一种通过改变增益光纤的掺杂浓度分布, 分散光纤激光的热效应, 从而提高激光输出功率的方法. 基于速率方程模型和热传导模型, 在光纤激光放大器输出功率大致相当的情况下, 对几种不同掺杂方式下增益光纤中的热分布和放大器的输出功率进行了数值模拟. 研究结果表明: 增益光纤的梯度掺杂可以优化光纤中的温度分布并提高光纤熔接点的稳定性; 同时兼具提高输出光束的光束质量、抑制光纤中非线性效应和模式不稳定的效果, 是提高光纤激光放大器输出功率切实可行的办法. 研究结果可以为高功率光纤激光器中增益光纤的设计提供一定的参考.     

基于垂直谐振腔结构的半导体光放大器理论分析

由新型垂直腔半导体光放大器（VCSOAs）器件结构出发,在反射模式和透射模式两种 情况下,计算了VCSOAs的分布布拉格反射堆（DBR）反射率、单程增益与增益、带宽的关系 ,其中DBR反射率的增大伴随着增益的上升,但也伴随着带宽的减小.通过引入增益-带宽 积的概念,以均衡增益与带宽.计算中表明:10 dB以上增益,50 GHz以上带宽可以实现. 计算结果与文献实验相吻合,对优化VCSOAs的结构设计和性能有所裨益.     

饱和放大情形下光纤参量放大器的增益和带宽特性研究

利用龙格库塔法数值求解非线性耦合方程,研究了单抽运光纤参量放大器在增益饱和区的增益谱特性.通过比较考虑抽运光损耗与忽略抽运光损耗增益谱的差别,分析了抽运光损耗对增益谱的影响.此外,给出了在饱和放大区,信号光的增益谱与光纤长度、输入信号光功率、抽运光波长与零色散波长偏离之间的关系.发现在饱和放大区,增益的整体水平有所下降,增益谱的可用带宽相对于小信号放大有所减少,增益谱在可用带宽范围内出现了旁瓣.这些结果将对工作在饱和放大区的单抽运光参量放大器的设计提供有益的帮助.     

Solvent effects on the gain of rhodamine 6G

The effect of solvents on the gain and the peaks of gain spectra is investigated for rhodamine 6G (R6G) under nitrogen laser pumping. The non-specific solute-solvent interaction for R6G is found to be mainly dispersive. Additional shifts produced for R6G in certain solvents are explained as due to hydrogen bonding. The gain characteristics are interpreted on the basis of the position and overlap of absorption and fluorescence spectra, the quantum yield, the absorption at the pumping wavelength and the refractive index of the solvent. For the solvents studied it is found that R6G has high gain in solvents with low refractive index and high polarity. Amongst the solvents studied the alcohols displayed the highest gain with methanol being the most suitable solvent. The lowest gain amongst the alcohols was with capryllic alcohol which gave a gain that was 69% of that obtained with methanol. Amongst all the solvents studied the lowest gain was with chloroform, being only 34% of the gain in methanol.     

Multi-wavelength hybrid gain fiber ring laser based on Raman and erbium-doped fiber

A stable and uniform multi-wavelength fiber laser based on the hybrid gain of a dispersion compensating fiber as the Raman gain medium and an erbium-doped fiber (EDF) is introduced. The gain competition effects in the fiber Raman amplification (FRA) and EDF amplification are analyzed and compared experimentaUy. The FRA gain mechanism can suppress the gain competition effectively and make the present multi-wavelength laser stable at room temperature. The hybrid gain medium can also increase the lasing bandwidth compared with a pure EDF laser, and improve the power conversion efficiency compared with a pure fiber Raman laser.     

门控分幅相机增益衰减特性

 分析了分幅相机增益衰减的理论模型,利用Mathematica软件模拟了增益随电脉冲传输时间指数衰减的曲线图。根据增益衰减理论,设计了测量增益衰减系数的实验。实验结果表明：分幅相机的平均增益按0.024 9 mm^-1指数衰减,电脉冲沿微带线传输的电压幅值衰减系数平均为0.003 56 mm^-1。得出实验数据中单条微带上增益并不完全符合增益指数衰减规律,而是在最后一帧图的增益有所回升,分析得出这是由电脉冲在微带末端连接处的反射引起的。经多次测量,电脉冲在微带线末端的平均值反射比为24.2％。对增益衰减状况的改善提出建议：采用良导体制作传输线,选取介质损耗小和绝缘性能好的材料作为填充介质,合理设计MCP微带线的厚度、微带宽度及微带与输出面的间距则可减小分幅相机增益的衰减。     

掠入射较高功率密度驱动Ni-like AgX射线激光的理论研究

 用系列程序对掠入射方式驱动亚稳态类镍银碰撞激发机制进行了研究。继低功率密度驱动获得有效增益系数为23.8 cm^-1结果之后,在4.3×10¹³ W·cm^-2较高功率密度驱动时,增益区移到驱动激光折返点附近,有效增益系数达到40 cm^-1以上,比正入射提高了2.4倍。用50 J激光能量驱动单靶,就能达到有效增益长度积为40的深度饱和增益。     

Focal Shift of Paraxial Gaussian Beams in a Left-Handed Material Slab Lens

Focal shift is inevitable in conventional lens systems due to the Fresnel number and angular aperture. In this Letter, we demonstrate that there is no focal shift when a paraxial Gaussian beam passes through a left-handed material slab lens without absorption or gain. However, the effect is exhibited in the presence of absorption or gain, and becomes larger as the absorption or gain increases. When the absorption is equal to the gain, the phenomenon of the focal shift caused by the gain is more obvious. In addition, the field distribution is not affected by the absorption or gain and always remains Gaussian both in internal and external focus planes.     

Graphene-tuned threshold gain to achieve optical pulling force on microparticle

We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method.It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.     

毫米波沟道梯型慢波结构行波管的线性理论

 在电子通道内引入一薄层空心电子注,对沟道梯型慢波结构行波管进行了线性理论研究,推导出了沟道梯型结构行波管的工作色散方程,计算了沟道梯型行波管的小信号增益和工作相速。计算结果表明：沟道梯型结构行波管每周期的增益高,带宽窄;当沟宽度由零增加到环内径的2倍时,增益减小量不足1%,这表明沟宽度对增益的影响不大;当脊高度增大10%时,增益增加62%,当环内径增大10%,增益减小57%,因此增益与脊高度正相关,与环内径负相关,且相关性十分明显。     

多束速调管的增益带宽

 研究了M个束、N个共振腔的多束速调管(MBK)的增益和带宽，得到了描述小信号增益和带宽与器件结构参数和电子束参数关系的公式，给出了在不同参数下增益随频率的变化曲线。分析了多腔对增益，多束对带宽的影响。计算结果表明：多腔可以提高增益；多束可以降低Q值，从而可以增中带宽，带宽增加工了3.6%，还可以提高增益；对于MBK，频率交叉调谐对增加带宽不如频率调谐好；空间电荷波只对增益有影响，对带宽没有影响。最后，预估一种L带多束速调管的增益带宽为8.1%。     

低增益准分子激光最佳透射率的研究

对于激光系统性能而言,谐振腔最佳透射率具有非常重要的作用。低增益、宽带脉冲准分子激光的最佳透射率条件与其激光抽运脉冲引起的增益脉宽有密切关系。提出了在激光四能级系统速率方程的基础上模拟低增益准分子激光的跃迁行为。并利用合理的近似,研究低增益脉冲准分子激光谐振腔的最佳透射率。给出了其在不同增益脉宽情况下统一的最佳透射率条件,并分析了以小信号增益系数为函数的最佳透射率变化规律。所得到的结论为：低增益、宽带脉冲准分子激光的最佳透射率情况和连续激光器有所不同。而是取决于增益脉宽和光子寿命之间的关系。上述结论得到了相应实验研究结果的证实。     

共聚焦生物芯片扫描仪中PMT电流增益的自动控制

根据共聚焦生物芯片扫描仪获得的图像,设计了计算机控制下的PMT电流增益自动控制系统.根据计算生物芯片图像的灰度分布与期望灰度分布的差异,得到期望灰度分布时PMT的期望电流增益,进而获得PMT的期望控制电压.一个12位数模转换器产生期望控制电压,自动控制PMT电流增益的调节,控制电压精度高达2 mV.实验结果表明,所设计的PMT电流增益自动控制系统可快速、准确地实现PMT电流增益调节,并具有稳定性高、抗干扰能力强的特点.