Optimization of optical parametric chirped pulse amplification with different pump wavelengths

Optical parametric chirped pulse amplification with different pump wavelengths was investigated using LBO crystal, at signal central wavelength of 800 nm. According to our theoretical simulation, when pump wavelength is 492.5 nm, there is a maximal gain bandwidth of 190 nm centered at 805 nm in optimal noncollinear angle using LBO. Presently, pump wavelength of 492.5 nm can be obtained from second harmonic generation of a Yb:Sr₅(PO₄)₃F laser. The broad gain bandwidth can completely support ∼6 fs with a spectral centre of seed pulse at 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning crystal angle for phase matching. The gain spectrum with pump wavelength of 492.5 nm is much better than those with pump wavelengths of 400, 526.5 and 532 nm, at signal centre of 800 nm.     

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.     

Generation of accurately synchronized pump source for optical parametric chirped pulse amplification

We demonstrate the generation of ultra-short pulses at 1064 nm by continuous-wave seeded non-collinear optical parametric amplification in a -barium borate crystal pumped by the second harmonics of a femtosecond Ti:sapphire laser. After two stages of seeded parametric amplifiers, the generated pulses at 1064 nm were accurately synchronized with the fundamental pump pulses, which could be used as seeding pulses for further amplification and then frequency doubling to produce an accurately synchronized pump source for optical parametric amplification of chirped pulses from the same Ti:sapphire laser. PACS 42.65.Re; 42.65.-k; 52.35.Mw     

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.     

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.     

Contrast limitation due to pump noise in an optical parametric chirped pulse amplification system

The contrast ratio of the recompressed output pulses in an optical parametric chirped pulse amplification system can be limited by temporal noise on the pump pulse. We present a simple analysis which can be used to estimate both the contrast ratio of this background noise and the duration of its pedestal. The estimated values compare well quantitatively with values derived using a more accurate computer simulation code.     

Chirped pulse amplification in single mode Tm:fiber using a chirped Bragg grating

We report femtosecond pulse generation and chirped pulse amplification in Tm:fiber. A mode-locked oscillator operating in the soliton regime produced 800 fs pulses with 5 nm spectral bandwidth, at 40 pJ pulse energy. This oscillator seeded a pre-amplifier that utilizes a Raman soliton self-frequency shift to produce wavelength tunable pulses with 3 nJ energy, reduced pulse duration of 150 fs, and increased bandwidth of 30 nm. For further amplification, the pulses were stretched up to 160 ps using a chirped Bragg grating (CBG). Stretched pulses were amplified to 85 nJ after compression in single-mode Tm:fiber and recompressed with the CBG as short as 400 fs. Compressed pulses were coupled into a highly nonlinear tellurite fiber to investigate the potential of this ultrashort pulse 2-μm fiber source as a pump for mid-IR supercontinuum generation.     

啁啾脉冲堆积及其放大特性

 根据啁啾脉冲堆积的原理以及模型介绍了两路脉冲堆积时脉冲的时间与频谱特性,分析了堆积脉冲产生时间与频谱调制,以及交叠区产生非线性频率啁啾的原因。通过非线性薛定谔方程,分析了堆积脉冲的放大特性,介绍了啁啾参量对放大结果的影响以及放大后堆积脉冲的频率啁啾的变化。研究表明,在堆积脉冲的放大过程中自相位调制效应非常明显,严重影响了脉冲的频谱与频率啁啾。     

Competing processes in optical parametric chirped pulse amplification

Optical parametric chirped pulse amplification (OPCPA) has the potential to revolutionise the generation of high power ultrashort optical pulses. In this paper, we present the results of a numerical investigation into processes that potentially compete with OPCPA. Specifically, we examine group velocity dispersion, non-degenerate operation, background noise, pump pulse fluctuations, and compressor error. We also discuss the “local approximation” and show that, in the case of OPCPA, it offers a substantial advantage in computational speed for minimal cost in accuracy. The overall conclusion is that OPCPA is fundamentally robust, and that the processes studied pose a less serious problem than might have been expected.     

啁啾脉冲堆积及其放大特性

根据啁啾脉冲堆积的原理以及模型介绍了两路脉冲堆积时脉冲的时间与频谱特性,分析了堆积脉冲产生时间与频谱调制,以及交叠区产生非线性频率啁啾的原因。通过非线性薛定谔方程,分析了堆积脉冲的放大特性,介绍了啁啾参量对放大结果的影响以及放大后堆积脉冲的频率啁啾的变化。研究表明,在堆积脉冲的放大过程中自相位调制效应非常明显,严重影响了脉冲的频谱与频率啁啾。     

Diode-pumped chirped pulse amplification to the joule level

The POLARIS project aims at the development of an all-diode-pumped, high-peak-power femtosecond laser system reaching the petawatt level. The laser amplifiers are based on pumping Yb³⁺-doped fluoride phosphate glass at 940 nm. Recently, stable operation of the first three amplifiers was achieved. Pulses with a bandwidth of 12 nm, which supports 135 fs pulses with energies up to 1.25 J, were generated in the third amplifier with a 12-pass configuration. The amplifier was pumped by 150 collimated high-power laser diodes. Successive polarization maintenance is used for a compact, stable, and convenient adjustable setup. Thermally induced abberations of lowest order were compensated by adaptive mirrors. PACS 42.55.Xi; 42.60.By; 42.70.Hj     

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     

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.     

啁啾脉冲放大系统展宽压缩器各阶色散分析

 通过在光程差中增加相位校正项,重新推导了更为完善的压缩器各阶色散解析式。并对压缩器的各阶色散作了光线追迹的模拟计算,得到与解析式完全一致的计算结果,从而验证了解析式的正确性。基于解析式和光线追迹的方法,更加系统完善地对比较常用的Offner展宽器的各阶色散进行了研究,分析了入射角、光栅与凹面镜距离对其各阶色散及剩余各阶色散的影响。同时,还对非匹配的展宽压缩系统的剩余色散的影响因素进行了讨论。     

高功率全光纤啁啾脉冲放大激光系统

采用基于非线性偏振旋转原理的光纤被动锁模激光器作为主振荡器。输出信号脉冲的重复频率为30 MHz,脉冲半高全宽为265 fs。信号脉冲通过全光纤啁啾脉冲激光放大系统展宽至100 ps后,经过1级芯径10 m的光纤预放大器和1级芯径50 m的光纤功率放大器将脉冲平均功率放大至10 W,斜率效率41.5%。输出脉冲经光栅压缩器将脉宽压缩至594 fs。     

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。     

高效三通光参量啁啾脉冲放大器

为了提高信号光与抽运光在时域上的匹配,提高放大系统的增益,提出了三通光参量啁啾脉冲放大的方法。实验中,信号光在一块晶体内被一抽运光在完全相位匹配的条件下放大了三次,总放大增益为3.7×107,能量晃动小于3%rms,放大后的信号光谱宽为30nm,压缩后的信号光脉宽为82fs。实验结果表明:采用三通光参量啁啾脉冲放大方法,有效地抑制了放大过程中参量荧光对放大过程的影响,在抽运光强为350MW/cm2时,参量荧光仅占输出总能量的1%。     

小宽带堆积啁啾脉冲传输放大特性

 采用啁啾脉冲堆积的方法可获得ns量级宽带整形激光脉冲,对堆积啁啾脉冲时间波形的影响因素及传输放大后脉冲波形与光谱形状的特性进行了研究。结果表明：在传输过程中脉冲的演化规律与窄带脉冲的演化规律基本一致,而且传输放大过程也不会改变脉冲的调制结构,但光谱形状在传输放大过程中发生了变化,初步认为是由非线性效应造成的;小宽带堆积啁啾脉冲具有与窄带脉冲基本一致的的增益水平。     

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。     

高功率全光纤啁啾脉冲放大激光系统

采用基于非线性偏振旋转原理的光纤被动锁模激光器作为主振荡器。输出信号脉冲的重复频率为30MHz,脉冲半高全宽为265fs。信号脉冲通过全光纤啁啾脉冲激光放大系统展宽至100ps后,经过1级芯径10μm的光纤预放大器和1级芯径50μm的光纤功率放大器将脉冲平均功率放大至10W,斜率效率41.5%。输出脉冲经光栅压缩器将脉宽压缩至594fs。