掺镱双包层脉冲光纤放大器的特性研究

 在高频及低频脉冲种子光的情况下讨论了掺镱双包层光纤放大器的输出特性.在有限差分法中,对于不同重复频率的脉冲种子光,需要设置不同的初始条件以快速计算得到稳定输出.本文给出了在高频和低频情况下设置初始条件的方法,并讨论了作为种子光的准连续高频高斯脉冲峰值功率与其等效连续光功率之间的关系,最后计算了种子光为高频及低频脉冲情况下的平均输出功率与泵浦功率的关系.     

高功率超短脉冲在增益介质中的传输特性

在考虑了增益介质的群速度色散、克尔非线性效应、增益饱和和增益谱后,推导出了光脉冲在介质中的传输方程.采用分步傅里叶变换法数值模拟了高功率线性啁啾脉冲在增益介质中的传输状态,并着重讨论了增益色散对光脉冲形状和功率谱的影响.计算结果表明:当高功率超高斯光脉冲在增益介质中传输放大时,脉冲形状变得尖锐,峰值向脉冲前沿移动;功率谱峰值向低频方向移动,并且在功率谱边缘形成非对称振荡结构;当介质的增益色散增大时,光脉冲光谱宽度变窄,峰值功率减小,因此对于宽光谱脉冲,增益色散将会导致损耗.     

硅波导受激喇曼散射放大信号光的数值模拟

提出了用连续泵浦光在硅波导中的受激喇曼散射对信号光进行放大的方法.建立了信号光和泵浦光在硅波导中传输的耦合方程,得到了计算信号光增益的理论模型.利用数值模拟结果,对泵浦功率沿波导的分布,信号光在不同波导长度以及输入功率情况下的增益等进行了分析和讨论.结果表明,适当增加波导长度和泵浦光功率可以得到较高喇曼增益的结论.     

利用相位模板实现数字全息超分辨成像

为了简化数字全息超分辨记录系统,分别在其物光和参考光部分引入一块相位模板,以获得垂直和倾斜方向照明物体的光束和具有不同载波频率的参考光束.当这些具有不同照射方向的光透过物体后,可以使CCD在位置固定的情况下记录到携带低频和高频信息的物体衍射场,不同载波频率的参考光则保证了高频和低频信息在复合全息图的频谱面上能够相互分离.实验结果证明,通过将记录到的物体高频和低频信息合成,可以获得超出系统衍射极限分辨率的再现像.     

利用相位模板实现数字全息超分辨成像

为了简化数字全息超分辨记录系统,分别在其物光和参考光部分引入一块相位模板,以获得垂直和倾斜方向照明物体的光束和具有不同载波频率的参考光束.当这些具有不同照射方向的光透过物体后,可以使CCD在位置固定的情况下记录到携带低频和高频信息的物体衍射场,不同载波频率的参考光则保证了高频和低频信息在复合全息图的频谱面上能够相互分离.实验结果证明,通过将记录到的物体高频和低频信息合成,可以获得超出系统衍射极限分辨率的再现像.     

光子晶体光纤中自相位调制效应对超高斯脉冲传输的影响

为了研究光子晶体光纤的微结构对其非线性光传输特性的影响,利用超格子法和光子晶体光纤中的光传输方程,计算了光子晶体光纤中的高斯光脉冲和超高斯脉冲的自相位调制谱.计算结果表明：高斯光脉冲和超高斯光脉冲的高频端比低频端均有较大的频谱展宽,而高斯光脉冲的频谱比超高斯光脉冲的频谱具有更大的中心峰值；超高斯光脉冲较高斯光脉冲有较广的频谱范围,它们的自相位调制展宽范围均随着传输距离的增加而增大.这些现象均可以利用自陡峭效应的理论加以解释.与传统光纤相比,高斯光脉冲在传统光纤中所受自相位调制效应的影响较小.     

掺Yb双包层光纤放大器的瞬态增益和频率响应

在理论上和实验上对掺Yb双包层光纤放大器(YDCFA)的瞬态增益特性进行了研究.建立了简化的瞬态增益基本模型,数值计算了低频光脉冲经过双包层光纤的放大波形,分析了瞬态增益饱和和恢复特性.在实验中对种子源放大的YDCFA的脉冲特性进行了分析,证实了其瞬态增益的低频响应特性.     

光参量振荡器的模型仿真

在傍轴近似条件下建立了OPO的数学模型,通过引入三波混频中时间与空间关系,采用分步傅里叶算法模拟了纳秒级脉冲和连续光波在谐振腔内的三波混频过程。理论模型中考虑了不同频率光波之间的色散关系,可以在高转换效率情况下分析不同泵浦脉冲功率、脉冲时长、腔镜透反射比以及不同种子光输入等情况下的输出波形、功率以及OPO阈值等特性。实验中采用掺杂MgO的周期性极化铌酸锂晶体（MgO∶PPLN）为非线性介质,在输入1.06 m泵浦激光脉冲能量为0.4 mJ时,产生3.8 m闲频光超过0.07 mJ输出,与数值模拟结果0.08 mJ较为符合。     

非线性光纤环镜在受激布里渊散射慢光级联系统中的可行性研究

基于非线性光纤环镜(NOLM)的脉冲压缩特性,分析了NOLM在基于受激布里渊散射(SBS)慢光级联系统中对延迟脉冲的影响.利用环形结构来模拟多次级联,有效地降低了系统的复杂度,得到了在不同抽运光功率和级联次数下脉冲的延迟输出特性.理论分析表明,NOLM可以有效地抑制SBS慢光级联系统中延迟脉冲的展宽,抽运光功率决定了展宽因子的变化趋势及最终稳定值的大小,展宽因子在级联4次时趋于稳定值,恰当选取抽运光功率可实现脉冲的零展宽延迟;改变抽运光功率和级联次数可以实现延迟量的连续可调,且延迟量理论上不受限制;增大抽 关键词： 慢光 脉冲压缩 非线性光纤环镜 受激布里渊散射     

光脉冲传输的Volterra级数模型收敛性质的研究

利用级数收敛理论, 推导出了基于Volterra级数理论的非线性薛定谔方程(NLSE)半解析解的收敛性质的表达式, 得到了保证级数收敛所允许的光脉冲最大输入功率、传输距离和所用Volterra级数模型的阶数以及与光纤参数之间的关系。利用数值计算得到了在给定光纤参数的情况下, 使用不同阶数的Volterra级数时为保证级数收敛所允许的光脉冲最大输入功率和传输距离的关系曲线, 结果表明, 使用不同阶数的Volterra级数来描述光脉冲传输时, 与阶数相对应的为保证级数收敛所允许的光脉冲最大输入功率也不同, 同时脉冲的宽度和光纤的色散都对为保证级数收敛所允许的光脉冲最大输入功率有影响。     

Passive coherent combination of two ultrafast rod type fiber chirped pulse amplifiers

Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs and 650 μJ pulses corresponding to 60 W of average power at a repetition rate of 92 kHz. Furthermore, at 2 MHz of repetition rate record coherent combining average powers of 135 W before and 105 W after compression are measured. A combining efficiency higher than 90% is maintained over the whole range of output powers and repetition rates investigated demonstrating the efficiency and robustness of the passive combining technique. The measured pulse-to-pulse relative power fluctuation at high energy is 2%, indicating that the system is essentially immune to environmental phase noise. We believe the passive combining method to be an attractive approach for compact multi-GW peak power femtosecond fiber-based sources.     

47 W, 6 ns constant pulse duration, high-repetition-rate cavity-dumped Q-switched TEM(00) Nd:YVO(4) oscillator

We report on a cavity-dumped Q-switched TEM(00) Nd:YVO(4) oscillator offering a unique combination of high power, constant short pulse duration, and high repetition rate, suppressing the gain dependence of pulse duration in classical Q-switched oscillators. Its performance is compared with that of the same oscillator operated in a classical Q-switched regime, demonstrating the much higher peak powers achievable with this technique, especially at high repetition rates. Up to 31 W of 532 nm green light was generated by frequency doubling in a noncritical phase matched LBO crystal, corresponding to 70% conversion efficiency.     

Comparison of electro-optical and acousto-optical Q-switched,high repetition rate Nd:GdVO<Subscript>4</Subscript> laser

The differences between the performances of electro-optical (EO) and acousto-optical (AO) Q-switched, diode pumped Nd:GdVO₄ laser at high repetition rates were detailed in this paper. The results revealed that EO Q-switch was more favorable to obtain short pulse width and high peak power laser than AO Q-switch under high repetition rate operation. The minimum pulse widths at 100 kHz were 20.2 ns under EO operation and 28.7 ns under AO operation, corresponding to peak powers of 3.1 kW and 2.2 kW, respectively. The corresponding values at 10 kHz were 5.3 ns, 9.0 ns and 77.4 kW, 45.6 kW, respectively.     

Microdrilling of metals using femtosecond laser pulses and high average powers at 515 nm and 1030 nm

We investigate the microdrilling of metals (stainless steel, copper and tungsten) for two different wavelengths, 1030 nm and 515 nm, in the regime of femtosecond laser pulses. An ytterbium-doped fibre CPA system provides high pulse energies (up to 70 μJ) and high repetition rates (up to 800 kHz), corresponding to high average powers of about 50 W, for this experimental study.     

Techniques for high power microwave sources at high average power

Experiments on CLIA (compact linear induction accelerator), capable of generating 750 kV and 10 kA into a matched load using magnetic switching to produce 60 ns long pulses, are described. As a first application, the authors used CLIA to drive a water-cooled L-band magnetron at repetition rates as high as 250 Hz with no breakdown or pulse shortening. This gives an average power of 6.3 kW. A short burst at 1 kHz demonstrates operation that would translate to an average power of approximately 25 kW. In this regime operation is not limited by gas build-up, electrode erosion or microwhisker depletion. Currently, the authors are operating on CLIA with a high current relativistic klystron. Beams with modulated current powers of approximately 1 GW have been generated at 100 Hz for bursts as long as 5000 pulses. It is concluded that there are no apparent obstacles to much higher average powers at higher peak powers     

Dark pulses with tunable repetition rate emission from fiber ring laser

We demonstrated the experimental observation of the dark pulses with tunable repetition rate from an erbium-doped fiber ring laser. A considerable length of high nonlinear fiber is incorporated into the fiber ring laser to enhance the nonlinear intensity. In our experiment, both bright and dark pulses can be observed under the conditions of appropriately setting of the device in the cavity. Further study showed that the dark pulse is formed due to the cross coupling between two different lasing wavelengths. Particularly, dark pulse-train with multiple repetition rates was observed from the laser cavity and the repetition rate switchable operation can be realized by simply adjusting the polarization controller (PC) in the cavity. The operation of multiple repetition rates of dark pulses was further experimentally investigated and detected as a result of pulse splitting of each component with different wavelength.     

LD连续泵浦Nd:YVO4声光调Q激光器

 利用半导体激光器（LD）连续单端泵浦Nd:YVO₄晶体，实现了声光调Q输出1 064nm的短脉冲。分析并用实验验证了不同透过率输出耦合镜及不同重复频率条件下，输出调Q脉冲能量、脉冲宽度及平均输出功率的规律。在泵浦功率为20.7W，重复频率为50kHz时，获得了最大平均输出功率为5.72W的脉冲，光 光转换效率为28%，斜效率为32.4%；在重复频率为10kHz时，最大单脉冲能量为0.286mJ，脉宽为22ns，峰值功率为13kW。     

Passively Q-switched Nd:YAG ring lasers with high average output power in single-frequency operation

Applying Cr(4+):YAG saturable absorbers, we demonstrate efficient passively Q -switched operation of diode-pumped Nd:YAG lasers with a maximum average output power of more than 800 mW. Pulse durations below 3 ns, energies of 70 muJ, and peak powers of 30 kW are observed with kilohertz repetition rates. Single-frequency operation is accomplished for all output powers by a nonplanar ring geometry.     

High-peak-power Tm-doped double-clad fluoride fiber amplifier

A diode-pumped Tm-doped double-clad fiber-optic amplifier is reported that provides up to 5 kW of peak power at pulse durations of 30 ns and a repetition rate of 33.5 kHz. When the repetition rate is increased to 123.6 kHz, the peak power drops to 1.5 kW, while the average output power of the amplifier stays at 6.5 W with a slope efficiency of 34.9%. As an amplifier the fiber can be saturated by a very low average launched input power of only 36 mW at 1.87 microm and yields the same average output power as in a fiber laser or amplified spontaneous emission source setup for all the repetition rates investigated. The peak powers reported are to the author's knowledge the highest generated by Tm-doped fiber lasers or amplifiers at repetition rates above 1 kHz with simultaneously short pulse durations of 30 ns.