利用脉冲负反馈压缩准分子激光脉冲

 分析了准分子激光脉冲在放大过程中的展宽现象。将饱和开关技术应用于放电泵浦激光器放大腔的放大压缩,发展了脉冲负反馈饱和压缩技术。利用该技术在天光一号系统前端LPX-150激光器上成功获得能量100 mJ、脉宽10 ns的脉冲输出,其空间分布均匀性保持在3%以内。这证明该技术可与无阶梯诱导非相干技术联合使用,在保证光束均匀性基础上进行脉冲压缩。     

利用脉冲负反馈压缩准分子激光脉冲

分析了准分子激光脉冲在放大过程中的展宽现象。将饱和开关技术应用于放电泵浦激光器放大腔的放大压缩,发展了脉冲负反馈饱和压缩技术。利用该技术在天光一号系统前端LPX-150激光器上成功获得能量100 mJ、脉宽10 ns的脉冲输出,其空间分布均匀性保持在3%以内。这证明该技术可与无阶梯诱导非相干技术联合使用,在保证光束均匀性基础上进行脉冲压缩。     

200 Hz高重复频率SBS脉宽压缩实验研究

受激布里渊散射(SBS)脉宽压缩是实现高峰值功率、短脉冲激光输出的重要途径之一,然而,目前SBS脉宽压缩仅限于1~10 Hz低重复频率激光器,限制了高重频短脉冲激光器在激光雷达、空间碎片探测以及目标成像等领域的应用。基于此,开展了高重复频率下的SBS脉宽压缩实验研究。设计搭建了高重复频率的主振荡放大激光器,开展了SBS二次级联脉宽压缩和SBS振荡放大双池脉宽压缩实验。通过SBS二次级联压缩实现了脉冲宽度从~32 ns压缩到~1.9 ns,脉宽压缩比达16倍;而通过SBS振荡放大双池结构实现了脉冲宽度从~4 ns压缩到376 ps,脉宽压缩比达10倍。实验结果表明,采用该超净封闭型SBS相位共轭镜,在Stokes光输出能量达50 m J时,无光学击穿现象,实现了在200 Hz高重复频率下的SBS脉宽压缩。     

KrF激光脉冲整形研究

 实验研究了脉冲堆积法对KrF激光的整形能力。利用受激布里渊散射(SBS)压缩脉冲获得了脉宽为3~5 ns的短脉冲，用4束激光堆积获得了脉宽为10~15 ns、平顶宽度为5~10 ns的整形脉冲。利用实测SBS脉冲数据，对脉冲堆积法进行了数值模拟，模拟的脉冲宽度为12.7 ns，平顶宽度为7.7 ns，该结果与实验相符。对脉冲堆积法的任意整形能力进行了模拟，讨论了脉冲宽度变化对整形的影响，发现脉宽变化在5%以内时，对整形脉冲的影响较小。对整形脉冲的放大进行了定性研究，结果表明：平顶脉冲通过放大器后，前沿部分放大较多，由于饱和作用，后沿放大较少；如果前端整形脉冲前沿为斜坡状，放大后可以得到近平顶的脉冲。     

激光二极管抽运电光调Q双通激光器中的光纤相位共轭

为了降低高重复频率脉冲固体激光器中热致光束畸变对光束质量的影响，在激光二极管抽运、电光调Q的Nd：YAG激光双通放大系统中对多模石英光纤相位共轭镜进行了实验研究。激光重复频率100Hz、脉宽20ns。实验结果表明：应用多模光纤能够显著改善放大级中热效应引入的波面畸变，双通获得近衍射极限的激光输出，并可大幅度压缩脉宽至7ns，达到了3：1的压缩比。在受激布里渊散射阈值附近，实验中观察到相位共轭光光斑剧烈闪烁，而随着注入光纤能量的增大，闪烁现象渐渐消失，输出激光能量的稳定度提高，在注入能量5．3mJ的情况下，获得了14％的能量不稳定度，此时的反射率和退偏率分别为32．6％和7％。     

掺镱光纤放大器泵浦脉宽优化

为抑制低重复频率高能脉冲光纤主振荡功率放大(MOPA)系统的放大自发辐射(ASE)效应,达到脉冲泵浦的最佳放大效果,需要对泵浦脉宽进行优化。基于求解速率方程和功率传输方程,理论研究了脉冲泵浦下掺镱光纤放大器上能级粒子数密度、光纤内存储能量、正反向放大自发辐射的瞬态响应。在给定的泵浦功率、光纤长度、纤芯面积和掺杂数密度等参数下,数值计算得到的优化泵浦脉宽为793 s。此外,实验测定了ASE的建立时间; 通过调节泵浦脉宽,测定了脉冲泵浦下掺镱光纤放大器的放大效果,实验中得到的泵浦脉宽的优化值为800 s,证明了数值模拟的正确性。     

液体相位共轭技术在高重复频率双程放大器中的应用

 采用丙酮液体作为相位共轭镜改善光束质量,实验研究了高重复频率二极管泵浦Nd:YAG双程放大器中液体SBS相位共轭技术的应用。结果表明：采用光束扫描方式,较明显地减小了液体介质热效应。激光器在重复频率400 Hz、注入能量40 mJ时,反射率达到65%。激光器使用SBS相位共轭镜后光束质量由2.3倍衍射极限提高到1.3倍衍射极限,激光脉宽由23 ns压缩到5 ns。     

激光诱导等离子体开关控制脉宽实验研究

 利用激光诱导等离子体开关技术,在1 064 nm的Nd：YAG固体激光器上获得了脉宽4.4~6.4 ns的短脉冲激光输出。激光电离空气产生的等离子体开关控制脉冲宽度时,聚焦透镜焦距越短,压缩后的脉宽越窄,但激光能量损耗越大。压缩后的激光脉宽与激光能量近似成双曲线关系。在控制脉宽光路的焦点处放置带孔的Cu薄片可抑制等离子体的扩散,得到了脉宽最短可达4.4 ns的激光输出。     

激光冲击强化激光器的研制

针对近年来发展的激光冲击强化技术,采用1级谐振8级放大的系统结构和模块化设计方法,研制出了激光冲击强化用短脉宽、大能量的Nd:YAG脉冲激光器,并对激光器技术指标进行了测试分析。在预热20 min后、环境温度变化小于2 ℃的情况下,单脉冲最大输出能量高达25 J,能量不稳定度小于3%,脉宽16~20 ns可调,脉宽不稳定度小于1 ns,光束发散角小于等于2.5 mrad,重复频率达5 Hz。对TC4钛合金进行激光冲击强化实验,大幅度提高了TC4钛合金试件表面的残余压应力。结果表明,研制的激光器各项性能良好。     

应用熔石英棒相位共轭镜的LD泵浦激光MOPA系统

 用熔石英棒作为相位共轭镜材料,在LD泵浦的激光MOPA系统中实现了在 100和400 Hz下的受激布里渊散射相位共轭。实验测得重复频率100 Hz时双通放大后的x和y方向的光束质量平方因子分别为1.74和1.66,最大反射率达到24.33% ,脉冲宽度从60 ns压缩到31.34 ns。重复频率400 Hz时双通放大后的x和y方向的光束质量平方因子分别为2.10和2.12,脉冲宽度从56.69 ns压缩到28.84 ns。     

2-(2''''-羟基苯基)间氮杂氧茚放大的自发辐射效应的实验和理论研究

报道了在氮分子激光泵浦下，激发态分子内质子转移分子2－（2＇－羟基苯基）间氮杂氧茚（HBO）环乙烷溶液放大的自发辐射（ASE）实验和理论研究。在环己烷溶液中，HBO的增益系数α（510um）约为1．2cm-1。在建立了HBO激发态分子内质子转移（ESIPT）的放大的自发辐射动态模型基础上，通过数值模拟得到了HBO的增益光谱和放大的自发辐射光谱，计算结果与实验很好相符，证实了HBO的酮式异构体的基态寿命更接近于260ns而非亚纳秒级。     

High-pulse-energy actively Q-switched Tm3+-doped silica 2 microm fiber laser pumped at 792 nm

A diode-pumped Q-switched Tm(3+)-doped double-clad silica fiber laser is reported providing average powers of up to 30 W at pulse widths of only 41 ns and repetition rates in the range of 10-125 kHz. Up to 270 microJ pulse energy was produced. Amplified spontaneous emission (ASE) buildup limits the maximum peak power, and the pump power and average output power at the point of ASE induced clamping were found to depend linearly on the repetition rate.     

Fully conductively cooled, diode-pumped Ho:Tm:LuLiF4 laser oscillator/amplifier

A fully conductively cooled and diode-pumped linear Ho:Tm:LuLiF laser oscillator can generate more than 1 J normal mode pulses at a 10 Hz pulse repetition rate where heat pipes are used for cooling pump diodes and laser crystal. As an amplifier, it can amplify the 80 mJ/180 ns pulses into 400 mJ pulses before the appearance of amplified spontaneous emission (ASE). The ASE threshold is about 5.6 J with a 40 mm long and side-polished laser crystal. For a 5 mJ input pulse and 5.6 J pump pulse, the double-pass gain exceeds 22.5. If the lateral surface of the laser crystal is fine ground, the ASE threshold can rise to higher than 8 J, but the efficiency will be lower due to large pump diffusion.     

Transient gain enhancement for a train of picosecond pulses in a large-aperture KrF laser amplifier

The heavily depleted steady-state gain in a large-aperture amplifier can be transiently enhanced by temporally suppressing the intra-cavity amplified spontaneous emission (ASE). In our previous experiments of amplifying two 10-ps pulses in a 29-cm-diameter KrF amplifier, we showed that output fluences of three times the saturation energy density E_sat were obtained at a pulse separation of 1.7 ns for full-filling beams, whereas it took 4 ns for 5-cm-diameter beams. Our recently developed time-dependent ASE code almost reproduced this observed quick gain recovery. In this paper, we report the experimental results of amplifying six 10-ps pulses in series to the saturation level in the large-aperture amplifier. The quick gain recovery was observed also for the pulse train. Short-pulse outputs of 3E_sat were obtained at a reduced pulse separation of only 1.5 ns. Received: 12 March 1999 / Published online: 19 May 1999     

Influences of ASE on the performances of Q-switched ytterbium-doped fiber lasers

The output characteristics of actively Q-switched ytterbium-doped fiber lasers (YDFL) are investigated in this paper. Our experimental results show that, the combined effect between the short switching time and the gain transient property of doped fiber causes the initial amplified spontaneous emission (ASE) power fluctuation, forming the multi-peak structure in the output pulse for either ring or linear cavity Q-switched YDFL. The pulse buildup time decreases with the rising of the pump. Moreover, since the broad-band ASE generated in the YDF is very high, it may saturate the doped fiber once the switch has been opened, making it difficult to achieve Q-switched laser oscillation for both fiber lasers. By using ASE filter to suppress the initial ASE, the gain supplied by the YDF can be greatly enhanced, which can not only decrease the threshold, but also greatly decrease the duration, and enhance the peak power of the Q-switched laser pulse as well. By using such an ASE filter, the Q-switched laser pulse with the peak power of 40.7 W and the duration of 30 ns has been achieved for the linear cavity YDFL pumped with 160 mW.     

Generation and measurement of >108 intensity contrast ratio in a relativistic kHz chirped-pulse amplified laser

We report on the generation and measurement of a > 10⁸ contrast ratio between main pulse and amplified spontaneous emission (ASE) from a relativistic kHz chirped-pulse amplified laser. We have enhanced the ASE contrast ratio as much as > 400 times by employing a pulse cleaner composed of a μJ preamplifier and a saturable absorber. A third-order cross-correlator with a dynamic range of > 10⁹ and a scanning range of up to 4 ns has been developed for the contrast measurement. Detailed analysis of the cross-correlation trace shows that the random noise of spectral phase generates 20-ps pedestal structure starting from 10⁻⁶ level of the main pulse.     

Amplified spontaneous emission from nitrogen laser pumped dye lasers

The nitrogen laser pumped dye laser output has been studied with emphasis on the behaviour of amplified spontaneous emission (ASE) with respect to the tuning wavelength, pump energy, dyes and their concentration and solvents. Spectral spread of ASE is narrower than fluorescence and its maximum is shifted towards the red side. However, lasing occurs beyond the ASE region. ASE is small at high gain wavelength and increases at the edges of the gain curve. Laser energy is highest at the ASE peak with minimum ASE present in the output. ASE is reduced with increased laser energy in the energy transfer dye lasers.     

小信号脉冲抽运时掺铒光纤自发辐射的研究

自发辐射(ASE)是掺铒光纤放大器(EDFA)的重要噪声源,对于由EDFA构成的光纤激光器有重要影响。理论与实践证明,它与抽运方式紧密相关,所以研究脉冲抽运时掺铒光纤(EDF)的自发辐射有重要的学术价值。同时,脉冲抽运对于EDFA锁模激光器的研究也有一定意义。从理论和实验两方面研究了小信号脉冲抽运时,抽运脉冲宽度和幅度对于EDF的自发辐射特性的影响,得到了小信号抽运时输出ASE噪声平均值的近似解析解。研究发现,小信号脉冲抽运时输出信号的幅度与抽运脉冲的宽度成正比。这个新现象可用于脉冲宽度的全光检测。     

Amplified spontaneous emission and power amplification in high-power DF laser systems

Amplified spontaneous emission （ASE） always occurs in high-power DF laser systems with master oscillator-power amplifier （MOPA） configuration. ASE not only reduces the energy extraction efficiency of the laser system, but also negatively influences its heat management. The interaction between the ASE flux and the coherent laser flux, as well as the effect of ASE on cuboid DF amplifiers, is studied using a finite difference method and an iterative arithmetic. In addition, the influence of ASE on coherent laser amplification is discussed in detail.     

Theoretical application of z-dependent gain coefficient to describe amplified spontaneous emission

Based on the geometrical modeling of the unified gain coefficient and the reported amplified spontaneous emission (ASE) output energy measurement ε(ASE) versus amplifying excitation length, l(AMP) in a KrF laser oscillator, we managed, as an example, to explain the ASE output energy behavior both numerically and analytically. In this approach, introducing the ASE gain-coefficient profile for the KrF laser, g(0,KrF)(ASE), was not avoidable. It was found that while the g(0,KrF)(ASE) profile follows the introduced gain-modeling formulation, it is, however, slightly lower than the KrF laser gain profile, g(0,KrF)(exp), deduced from the measurements reported by different researchers. The present approach, up to the present time, is able to explain all of the existing ambiguities on understanding the ASE behavior.