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.     

用于产生亚12fs脉冲的脉冲波前匹配的超宽带光学参量啁啾脉冲放大器

研究和建议了一种用于产生亚12fs脉冲的基于脉冲波前匹配的LBO超宽带光学参量啁啾脉冲放大器。实验结果表明LBO超宽带光学参量啁啾脉冲放大器可以输出大于60nm(FWHM)的增益光谱带宽，为了利用这种放大器产生转换限制的脉冲输出，给出了一种将超宽带光学参量啁啾脉冲放大器与脉冲波前匹配相结合的方法，这种方法等价于信号光脉冲波前无斜置的放大，克服了超宽带参量啁啾脉冲放大器中由于信号光的脉冲波前斜置而导致很难获得最短压缩脉冲输出的缺陷，从而允许产生转换限制的亚12fs脉冲。     

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。     

Broadband femtosecond OPCPA system driven by the single-shot narrow-band iodine photodissociation laser SOFIA

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800?nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 10⁸ times. The amplified spectral bandwidth of 68?nm corresponds to the pulse duration of 14?fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (<0.1?cm^?1) and, therefore, the conventional chirped-pulse amplification technique does not lead to pulse durations at the femtosecond level.     

Optical parametric chirped pulse amplification based on photonic crystal fibre

A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated.A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier.After the amplified pulses pass through the LBO crystal,the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA).The 850-nm chirped signal light gain from the stretcher is 1.5×10 4 in the first-stage OPA while it is 120 in the second-stage OPA.The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8×10 6.     

Femtosecond pulse parametric amplification at narrowband high power gas laser pumping

In ultrashort pulse amplification a narrowband gas pump pulse laser has been used for the first time. An all-stage optical parametric chirped pulse amplifier (OPCPA) was driven by a single-shot iodine photodissociation laser. For the first time a broadband amplification was achieved in potassium dihydrogen phosphate crystal at 800 nm seeding. Ti:sapphire laser pulses stretched from 12.5 fs to 250 ps were amplified and compressed to 27 fs at a 0.5 TW output power. The results suggest using narrowband high power gas lasers as OPCPA drivers to generate petawatt beams.     

基于预啁啾控制的极宽带光参量放大

在以飞秒钛宝石放大系统的倍频光为抽运光和超连续白光为信号光的光参量放大中,针对抽运光的宽带特点,分析了一种新的极宽带相位匹配方法.结果表明,10nm的抽运光带宽可得到近400nm的相位匹配带宽,若抽运光带宽达到20nm,相位匹配带宽就能达到近600nm.零色散波长为800nm的光子晶体光纤产生的超连续谱经光纤传输后为二次啁啾,宽带抽运光经棱镜对展宽具有线性啁啾,满足了极宽带相位匹配方法所需要的光谱分布.理论计算了对输入脉冲进行预啁啾控制应选择的光纤长度和棱镜对在光路中的插入量,为实现极宽带光参量放大提供了 关键词： 啁啾 极宽带相位匹配 光参量放大 光子晶体光纤     

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。     

光参量啁啾脉冲放大中时间同步抖动对增益稳定性的影响

在考虑了光参量啁啾脉冲放大中的脉冲波形、相位失配和时间同步抖动情况下,给出了计算光参量啁啾脉冲放大增益特性更为完善的三波耦合理论模型。并在1 ns的时间同步抖动情况下,对比分析了光参量放大在小信号放大及饱和放大时的增益稳定性。光参量放大的时间同步抖动对增益影响非常大,使放大信号光脉冲的增益光谱发生了明显的偏移,波形不对称和整个增益降低;并且信号光光谱越宽,光参量放大间的时间同步抖动对其增益影响越严重;但随着参量放大增益饱和的出现和加深,信号光和抽运光之间的同步时间抖动对放大信号光的输出强度影响减弱,即在饱和放大处可以获得更稳定的放大信号光输出。     

Direct measurement of the effective input noise power of an optical parametric amplifier

The spontaneous fluorescence background in optical parametric amplifiers is generally attributed to the zero‐point fluctuations of the electromagnetic field. These are amplified in parallel to the seed light and lead to an uncompressible superfluorescence background that deteriorates the contrast in optical parametric chirped pulse amplifiers (OPCPA). The absolute level of the underlying parametric fluorescence has not been reported so far. Comparing the fluorescence to low level cw seed light and quantitatively monitoring the output of a noncollinear optical parametric amplifier for both sources, the level is now determined. In a situation of 50 nm visible output bandwidth and low Gaussian spatial modes about 58 photons are found in the signal direction within the femtosecond time window of the amplifier. The superfluorescence level is observed to be proportional to the pump area for constant signal amplification. The implications for the background in high power OPCPA are discussed.     

Bandwidth enhancement for parametric amplifiers operated in chirped multi-beam mode

In this paper we discuss the bandwidth enhancement that can be achieved in multi-Joule optical parametric chirped pulse amplification (OPCPA) systems exploiting the tunability of parametric amplification. In particular, we consider a pair of single pass amplifiers based on potassium-dideuterium-phosphate (DKDP), pumped by the second harmonic of Nd:glass and tuned to amplify adjacent regions of the signal spectrum. We demonstrate that a bandwidth enhancement upto 50% is possible in two configurations; in the first case, one of the two amplifiers is operated near its non-collinear broadband limit; to allow for effective recombination and recompression of the outgoing signals this configuration requires filtering and phase manipulation of the spectral tail of the amplified pulses. In the second case, effective recombination can be achieved simply by spectral filtering: in this configuration, the optimization of the parameters of the amplifiers (pulse, crystal orientation, and crystal length) does not follow the recipes of non-collinear OPCPA.     

大信号增益区的宽带OPCPA系统特性分析

利用大啁啾信号光脉冲的光谱在时域内的分布特点,采用四阶龙格-库塔算法对宽光谱的光参量啁啾脉冲放大（OPCPA）激光器特性进行了数值分析。以LBO晶体为增益介质,信号光脉冲宽度取100 ps、啁啾系数为1 000,中心波长为800 nm;泵浦光的中心波长为532 nm,脉宽为100 ps。数值计算结果表明：信号光的非线性相位变化的中心部分为线性分布区,且随增益饱和的程度增大而增大;系统的功率转换效率有准振荡结构,且其第一个极值点为系统能量最大的转换率点;随着系统进入增益饱和区,压缩光脉冲的对比度明显降低,预脉冲长度显著增大。     

Optimization of Pulse Temporal Contrast in Optical Parametric Chirped Pulse Amplification

In optical parametric chirped pulse amplification （OPCPA）, the degradation of temporal contrast of the compressed signal pulse mainly results from spectral clipping in the grating stretcher with finite size of the optics, parametric fluorescence （PF） and the spectral variations transferred from temporal fluctuation of the pump pulse. The temporal contrast of the recompressed amplified pulse in the OPCPA system is studied numerically and a number of solutions are considered and optimized to achieve the highest temporal contrast.     

基于预啁啾控制的极宽带光参量放大

在以飞秒钛宝石放大系统的倍频光为抽运光和超连续白光为信号光的光参量放大中，针对抽运光的宽带特点，分析了一种新的极宽带相位匹配方法.结果表明，10nm的抽运光带宽可得到近400nm的相位匹配带宽，若抽运光带宽达到20nm,相位匹配带宽就能达到近600nm.零色散波长为800nm的光子晶体光纤产生的超连续谱经光纤传输后为二次啁啾，宽带抽运光经棱镜对展宽具有线性啁啾，满足了极宽带相位匹配方法所需要的光谱分布.理论计算了对输入脉冲进行预啁啾控制应选择的光纤长度和棱镜对在光路中的插入量，为实现极宽带光参量放大提供了     

High energy and long pulse generation with high-birefringence photonic crystal fibre and laser-diode pumped regenerative amplifier

We report on the generation of a high energy and long pulse for pumping optical parametric chirped-pulse amplification (OPCPA) by a high-birefringence photonic crystal fibre (HB-PCF) and a laser-diode-pumped regenerative chirped pulse amplifier. Using the femtosecond pump pulse centred at 815~nm, a 1064~nm soliton pulse is produced in the HB-PCF. After injecting it into an Nd:YAG regenerative amplifier with the glass etalons, a narrow-band amplified pulse with an energy of $\sim $4~mJ and a duration of 235 ps is achieved at a repetition rate of 10~Hz, which is suitable for being used as a pump source in the 800~nm OPCPA system.     

High-power output from a compact OPCPA laser system

With a tabletop hybrid Nd:YAG-Nd:glass laser as pump source, a compact optical parametric chirpedpulse amplification(OPCPA)laser system with a peak output power of 16.7 TW and a pulse duration of120 fs has been demonstrated.Chirped pulses are amplified from 50 pJ to more than 3.1 J with an energygain of above 6×10~(10)by three LBO optical parametric amplifiers with a pump energy of 12.4 J at 532nm.After compression, a final output of 2.0-J/120-fs pulse is obtained. To the best of our knowledge,itis the highest peak output power from an OPCPA laser so far.In addition, a practical design of 1-PWlaser system based on the technique of OPCPA is also proposed.     

啁啾匹配OPCPA方案用于消除超短激光脉冲的预脉冲

采用了一种利用啁啾匹配光参量啁啾脉冲放大（OPCPA）技术来消除泵浦脉冲时间窗口内的预脉冲的方法,并对该方法展开了数值模拟研究。分析了泵浦光脉冲形状、预脉冲提前时间等因素对预脉冲消除效果以及信噪比提升情况的影响。通过与传统的非共线OPCPA方案对比,发现啁啾匹配OPCPA方案可以消除掉离主脉冲更近的预脉冲,且它对预脉冲的消除效果受泵浦光脉冲形状的影响较小。     

光学参变啁啾脉冲放大相位失配啁啾脉冲频谱整形新方法

相位匹配是实现高效光学参变啁啾脉冲放大(OPCPA)能量转换的关键之一,通过对几种常用非线性晶体的光学参变啁啾脉冲放大过程进行数值模拟研究,结果表明一定程度的相位失配不但能增加光学参变啁啾脉冲放大增益带宽,而且会使啁啾脉冲光谱强度分布中间凹陷。提出利用光学参变啁啾脉冲放大相位失配放大作为啁啾脉冲频谱整形的新方法,通过理论分析和模拟计算,找到了光学参变啁啾脉冲放大相位失配啁啾脉冲频谱整形效果的控制量;并对几种常用非线性晶体在简并、近简并、非简并等条件下的光学参变啁啾脉冲放大相位失配放大特性进行了比较。     

啁啾匹配OPCPA方案用于消除超短激光脉冲的预脉冲

采用了一种利用啁啾匹配光参量啁啾脉冲放大（OPCPA）技术来消除泵浦脉冲时间窗口内的预脉冲的方法,并对该方法展开了数值模拟研究。分析了泵浦光脉冲形状、预脉冲提前时间等因素对预脉冲消除效果以及信噪比提升情况的影响。通过与传统的非共线OPCPA方案对比,发现啁啾匹配OPCPA方案可以消除掉离主脉冲更近的预脉冲,且它对预脉冲的消除效果受泵浦光脉冲形状的影响较小。     

光参量啁啾脉冲放大中时间同步抖动对增益稳定性的影响

 在考虑了光参量啁啾脉冲放大中的脉冲波形、相位失配和时间同步抖动情况下,给出了计算光参量啁啾脉冲放大增益特性更为完善的三波耦合理论模型。并在1 ns的时间同步抖动情况下,对比分析了光参量放大在小信号放大及饱和放大时的增益稳定性。光参量放大的时间同步抖动对增益影响非常大,使放大信号光脉冲的增益光谱发生了明显的偏移,波形不对称和整个增益降低;并且信号光光谱越宽,光参量放大间的时间同步抖动对其增益影响越严重;但随着参量放大增益饱和的出现和加深,信号光和抽运光之间的同步时间抖动对放大信号光的输出强度影响减弱,即在饱和放大处可以获得更稳定的放大信号光输出。