Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb³⁺-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 × 10⁷ at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse.     

光参量啁啾脉冲放大的逆问题

针对光参量啁啾脉冲放大的逆问题,即如何在给定输出信号光脉冲波形的前提下,通过计算得到输入信号光脉冲波形,提出了相应的计算模型和方法.以分步傅里叶变换和四阶龙格-库塔法为基础,通过数值拟合等方法,建立了输入-输出信号光强之间的定量关系.分别以预期输出信号光脉冲为啁啾高斯脉冲以及具有特定形状的整形脉冲为例,通过逆算得到了相应的输入信号光脉冲波形.研究结果表明,该逆算方法具有原理简单、计算快速准确等优点,可为激光脉冲整形设计提供参考. 关键词： 光参量啁啾脉冲放大 逆问题 啁啾脉冲 脉冲整形     

Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992,optical parametric chirped pulse amplification(OPCPA)became the most promising method for the amplification of broadband optical pulses.In the meantime,we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers.The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level.Meanwhile,the output pulse duration based on optical parametric amplification has entered the range of fewoptical-cycle field.In this paper,we overview the basic principles,trends in development,and current state of the ultrashort and laser systems based on OPCPA,respectively.     

Numerical studies of optical parametric chirped pulse amplification

Based on the coupled wave equations, optical chirped-pulse parametric amplification (OPCPA) is simulated and its characteristics are investigated under the conditions of small-signal and pump depletion. The influence of the group-velocity mismatch and the phase mismatch among the three waves on the process of the amplification are discussed, respectively. Compared with the conventional chirped-pulse amplification system, synchronization between pump and signal-pulses is a crucial issue in OPCPA. The requirement on Δτ_p–s as well as the stability of the system is investigated.     

自由电子激光放大啁啾脉冲的数值模拟

 利用1维非定态程序对单程自由电子激光(FEL)放大器放大线性啁啾脉冲的过程进行了数值模拟,得到了不同啁啾参数的脉冲通过FEL放大器的增益曲线,计算了不同啁啾参数的脉冲被单程FEL放大器放大后的腔外压缩情况。通过对数值模拟结果的定性分析得出：影响输出脉冲宽度和峰值功率的主要因素是FEL放大器的增益线宽和啁啾参数,并以此说明,通过先使用FEL放大器放大啁啾脉冲、然后再将其在腔外压缩的方法产生超短脉冲FEL是可行的。     

BBO，LBO，KDP晶体光参量啁啾脉冲放大特性的比较研究

 对BBO，LBO，KDP晶体I类非共线匹配下的光参量啁啾脉冲放大的相位匹配、参量范围、增益特性等进行了理论分析，重点对BBO和LBO的光参量啁啾脉冲放大特性进行了比较。结果表明对于以光参量啁啾脉冲放大系统代替800nm中心波长的Ti:sappire再生放大系统，用BBO晶体可获得更宽的增益带宽，而对1 053nm中心波长的种子光用LBO晶体更好。     

Phase matched scanning optical parametric chirped pulse amplification based on pump beam deflection

Combined with the optical beam deflection, a novel approach of phase matched broadband scanning optical parametric chirped pulse amplification(OPCPA) was proposed. For this scheme, there was no superfluous operations to the chirped signal pulse which propagated in a changeless direction straightforward, but the pump beam were deflected in space with time by passing through a KTN crystal, which was applied with varied driving voltage. The theories of phase matching of each chirped signal frequency based on pump beam deflection was analyzed detailedly. And the type-I amplification of chirped signal with 800 nm central wavelength and 20 nm bandwidth pumped by 532 nm in BBO crystal was simulated as a case in point. The simulation results showed that the spectral distribution of chirped signal pulse was almost the same as the initial form, i.e., there was nearly no narrowing on the amplified spectrum by using of the scanning OPCPA based on pump beam deflection. In addition, the simulations demonstrated that it was worth minimizing the voltage deviation applied to KTN crystal as much as possible for the sake of better waveform, larger bandwidth and higher conversion efficiency of amplified signal pulse in the proposed scanning OPCPA.     

ps参量放大效应

本文报道用0.53μm波长超短脉冲序列泵浦角度调谐的LiNbO_3参量晶体,获得1%单程参量放大能量转换效率,并在0.8～1.6μm范围测得参量信号光和空载光波长调谐曲线.     

光参量啁啾脉冲放大增益特性研究

 通过对非线性三波耦合方程组进行数值求解，研究了光参量放大的增益特性及饱和放大特性。给出了泵浦光、信号光参数对参量增益的影响及其与晶体饱和长度的关系。且OPA具有传统CPA系统所不具有的优点，将有可能取代传统的CPA系统而作为超短超强激光系统的新型前端。     

Bandwidth and stability enhancement of optical parametric amplification using chirped ferroelectric superlattice

We report a theoretical analysis and numerical simulation of bandwidth and stability enhancement in optical parametric amplification (OPA) when using chirped periodically poled KTiOPO₄. Calculation results show that the bandwidth and stability are enhanced significantly by the use of a chirped grating. Temperature-gradient and fanned gratings are introduced and chirp factors of them are deduced and calculated. The use of a fanned grating flattens the Quasi-phase-matching response and improves the efficiency. Finally, we propose a method to reduce the instability induced by an unstable pump.     

基于光束偏转的扫描式宽带光参量啁啾脉冲放大

光参量啁啾脉冲放大(OPCPA)是超短激光脉冲领域的重要技术之一,增大增益带宽对提高OPCPA的转换效率、实现宽带光参量放大具有重要的意义.本文将光束偏转和非共线OPCPA有机结合,提出了基于光束偏转的扫描式宽带OPCPA模型.分析了通过光束偏转来时刻改变非共线角,以保证各频率成分的相位匹配,从而增大增益带宽的基本原理.采用提出的扫描式宽带OPCPA,针对800 nm中心波长、带宽约为100 nm信号光的光参量放大进行了数值计算.结果表明:经过扫描式OPCPA后,信号光的带宽与放大之前几乎相同,光谱没有窄化;扫描式OPCPA比固定非共线角方式的放大极大地增加了增益带宽和转换效率,实现了宽带的光参量放大;要满足信号光各频率成分的相位匹配,达到最大的增益带宽和转换效率,需要尽量减小加载到钽铌酸钾(KTa_(1-x) Nb_xO_3, KTN)电光晶体上的电压抖动和电压延时.     

Backward Raman amplification in plasmas with chirped wideband pump and seed pulses

Chirped wideband pump and seed pulses are usually considered for backward Raman amplification(BRA)in plasmas to achieve an extremely high-power laser pulse.However,current theoretical models only contain either a chirped pump or a chirped seed.In this paper,modified three-wave coupling equations are proposed for the BRA in the plasmas with both chirped wideband pump and seed.The simulation results can more precisely describe the experiments,such as the Princeton University experiment.The optimized chirp and bandwidth are determined based on the simulation to enhance the output intensity and efficiency.     

啁啾匹配和同步抖动对光参量啁啾脉冲放大的影响

通过研究光参量啁啾脉冲放大过程转换效率随泵浦光啁啾参数的变化,以及信号光和泵浦光波长的对应关系,确立了信号光和泵浦光同步时实现线性啁啾匹配的方法。以磷酸二氢钾作为非线性晶体,研究了信号光和泵浦光之间的线性啁啾匹配和时间同步抖动对光参量啁啾脉冲放大后信号光脉冲波形和转换效率的影响。结果表明：在时间同步的情况下,线性啁啾匹配时的信号光脉冲波形很对称,转换效率也较高;在同步抖动程度一定的情况下,不同泵浦光啁啾参数时,信号光的增益及放大后的脉冲波形差异较大;在线性啁啾匹配程度一定时,信号光和泵浦光时间同步抖动越严重,放大信号光的脉冲波形变化越大,信号光增益越小,且转换效率也越低。     

啁啾光脉冲的自相位调制效应对压缩光脉冲的影响

 在超强激光系统中,对比度和本底宽度是压缩光脉冲极为重要的指标。在啁啾脉冲放大系统的压缩阶段,在啁啾脉冲宽度为141ps,啁啾系数为1000,B积分值分别为0,1和2的情况下,模拟了自相位调制效应（SPM）对压缩脉冲的峰值光强、脉冲宽度和本底宽度的影响。结果表明：在B积分值为2的条件下,若不补偿非线性色散,压缩脉冲的峰值强度降为无自相位调制效应时的65%左右,脉冲宽度约为种子脉冲宽度的2倍,本底宽度则增加到原来的3倍左右;在B积分值大于0.5的情况下,本底宽度和B积分值近似成线性关系。     

Numerical analysis of spatial distortions in a single-grating chirped pulse amplification system

A numerical study of spatial distortions of a laser beam after propagation through an optical single-grating chirp pulse amplification (CPA) system was developed. This study is based on numerical simulation using the ray-tracing model from Rayica module of MATHEMATICA and it relates the behavior of the aberrated beam in terms of spatial distortions (eg. spatial chirp and pulse front tilt) in case of grating incident angle variation. The results are relevant for different applications which use CPA systems with needs of high quality laser beam profile.     

光参量啁啾脉冲放大过程中脉冲特性理论研究

 通过数值求解非线性三波耦合方程组,并利用色散致啁啾引起的瞬时频率与时间的关系,模拟了啁啾脉冲在光参量放大过程中的脉冲波形和频谱形状的变化关系,以及通过压缩器的脉冲形状。模拟结果表明：啁啾脉冲在光参量放大过程中的时域宽度和频谱有很小程度的加宽,但基本上不影响放大后脉冲的压缩及信噪比。     

光参量啁啾脉冲放大过程中脉冲特性理论研究

通过数值求解非线性三波耦合方程组,并利用色散致啁啾引起的瞬时频率与时间的关系,模拟了啁啾脉冲在光参量放大过程中的脉冲波形和频谱形状的变化关系,以及通过压缩器的脉冲形状。模拟结果表明：啁啾脉冲在光参量放大过程中的时域宽度和频谱有很小程度的加宽,但基本上不影响放大后脉冲的压缩及信噪比。     

Narrowing behavior of chirped pulses with small Fresnel number in focusing systems

Based on the diffraction integral and Fourier transform, the fields of chirped pulses passing through a thin lens are derived. Influences of Fresnel number and chirp parameter on the transverse intensity distributions of the chirped pulses at focal plane are illustrated with numerical results. Also, effect of pulse duration on the intensities is investigated. It is found that the width of transverse intensity distribution of the chirped pulses decreases with increasing the chirp parameter and the narrowing behavior presents more obvious with smaller Fresnel number. A physical explanation for the narrowing behavior is given on the basis of a simplified form of the field expression.     

Optimized amplification of femtosecond optical pulses by dispersion management for octave-spanning optical frequency comb generation

We report a method for optimizing the amplification of femtosecond optical pulses by using dispersion management. The amount of dispersion provided to the seed optical pulse of an erbium-doped fiber (EBF) has an optimal region that enhances the output power of an amplifier. The power enhancement is accompanied by spectral broadening, which originates from adiabatic narrowing in the erbium-doped fiber. The amplified optical pulses can be used to generate an octave-spanning optical frequency comb (OFC) by employing a highly nonlinear fiber (HNLF).     

泵浦光波形和脉宽对飞秒激光对比度的影响

 采用宽带数值模型，应用四阶龙格-库塔数值算法对三波耦合方程进行数值分析，研究了泵浦光的波形和脉宽在提高光参量啁啾脉冲放大系统输出飞秒激光对比度的作用。结果表明：在泵浦光脉宽较小的条件下，采用平滑的泵浦光波形更有利于提高飞秒激光对比度；在泵浦光脉宽较宽时，飞秒激光对比度得到很好地提高，而对泵浦光波形不敏感；但继续提高泵浦光脉宽并不能进一步改善飞秒激光对比度，而系统的转换效率却显著降低。