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.

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.

Generation of 17-TW 23-fs Pulses with a Two-Stage Ti：Sapphire Amplifier at Repetition Rate 10 Hz

We have developed a two-stage Ti：sapphire amplifier system which can produce 17- TW/23-fs pulses at a repetition rate 10Hz. A birefringent plate is used in the regenerative amplifier to alleviate gain narrowing, while an all- reflective cylindrical-mirror-based pulse stretcher and an acousto-optic programmable dispersive filter （AOPDF） are used to compensate for the higher order dispersion of the system.

Wavefront evolution of the signal beam in Ti:sapphire chirped pulse amplifier

We studied the evolution of wavefront aberration(WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification(CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.

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 -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-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz

A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification（CPA） technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied.We find that the compressed pulse duration is dependent on the amplified energy,the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ,while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ.The measured energy fluctuation is approximately 0.46% root mean square（RMS） over 2 h.The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines,medical therapy,and scientific studies.

High-power all-fiber linearly polarized Yb-doped chirped pulse amplifier based on active polarization control

High-power ultrafast laser amplification based on a non-polarization maintaining fiber chirped pulse amplifier is demonstrated.The active polarization control technology based on the root-mean-square propagation(RMS-prop)algorithm is employed to guarantee a linearly polarized output from the system.A maximum output power of 402.3 W at a repetition rate of 80 MHz is realized with a polarization extinction ratio(PER)of>11.4 dB.In addition,the reliable operation of the system is verified by examining the stability and noise properties of the amplified laser.The M2factor of the laser beam at the highest output power is measured to be less than 1.15,indicating a diffraction-limited beam quality.Finally,the amplified laser pulse is temporally compressed to 755 fs with a highest average power of 273.8 W.This is the first time,to the best of our knowledge,that the active polarization control technology was introduced into the high-power ultrafast fiber amplifier.

Compact pulsed thulium‐doped fiber laser for topographical patterning of hydrogels

We report the generation of high energy 2μm picosecond pulses from a thulium-doped fiber master oscillator power amplifier system.The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber(LMA-PCF).The amplifier output is a linearly-polarized 1.5 ns,100 kHz pulse train with a pulse energy of up to 250μJ.Pulse compression was achieved with(2+2)-pass chirped volume Bragg grating(CVBG)to obtain a 2.8 ps pulse width with a total pulse energy of 46μJ.The overall system compactness was enabled by the all-fiber amplifier design and the multi-pass CVBG-based compressor.The laser output was then used to demonstrate high-speed direct-writing capability on a temperature-sensitive biomaterial to change its topography(i.e.fabricate microchannels,foams and pores).The topographical modifications of biomaterials are known to influence cell behavior and fate which is potentially useful in many cell and tissue engineering applications.

A new method for measuring the pulse-front distortion of arbitrary shapes in high-power ultrashort laser systems

We present a new method that can be used to calculate pulse-front distortion by measuring the spectral interference of two point-diffraction fields in their overlapped district. We demonstrate, for the first time, the measurement of the pulse-front distortion of the pulse from a complex multi-pass amplification system, which exists in almost all high-power laser systems, and obtain the irregular pulse-front distribution. The method presented does not need any reference light or assumption about the pulse-front distribution, and has an accuracy of several femtoseconds.

多脉冲加载下PBX装药的应力放大效应

针对弹体侵彻过程中装药常常受到多脉冲载荷作用的问题,提出了一种装药多脉冲加载装置,研究了多脉冲加载下装药的应力放大效应。基于集中质量法建立了多脉冲加载装置的等效弹簧模型,对产生应力放大的条件进行了探讨。结果表明,多脉冲载荷频率与装药固有频率匹配时系统发生共振,装药产生响应放大,放大倍数随结构间隙宽度的增加而降低。装药多脉冲加载下存在一个时间区间,撞击加载的发生时刻落在该区间内时系统可产生放大效果。对高聚物黏结炸药(polymer bonded explosive,PBX)模拟材料,实现了实验室条件下应力幅值百兆帕、脉冲间隔毫秒级、脉冲次数3次且幅值逐渐放大的多脉冲载荷加载。

用于多模态非线性光学显微成像的增益管理放大全光纤飞秒激光技术

基于增益管理非线性放大的机制,求解非线性薛定谔方程和速率方程对脉冲在增益光纤中的传播过程进行仿真,研究了脉冲在增益光纤中的演化过程。结果表明,优化预啁啾量和种子光强度,可改变脉冲在增益光纤中的增益曲线。在动态增益曲线与非线性效应的共同作用下,输出光脉冲的频谱会迅速展宽数倍并带有线性啁啾,进而脉冲可被压缩至近傅里叶变换极限。为验证该超短脉冲产生方式的可行性,采用仿真结果中的最佳参数设置,成功设计并搭建了一台高能量、短脉宽、高质量的超快光纤光源。该光源可实现中心波长为1060 nm、重复频率为35 MHz、平均功率为267.4 mW以及脉冲宽度仅为39.5 fs的激光输出,与仿真结果高度一致。同现有的超短脉冲产生方式相比,本实验装置的结构更简单、造价更低、装置更紧凑、产生光束品质更佳。

增压式脉冲水射流瞬时压力特性试验研究

射流压力特性决定其冲击能力,针对增压式脉冲水射流瞬时压力特性尚不明确这一问题,利用自行研制的增压式脉冲水射流压力采集系统开展试验,探究进水压力、进油压力及喷嘴直径等参数对增压腔压力特性的影响规律。试验结果表明:随着进水压力的提升,峰值压力不变,谷值压力同步提升,频率增大,增压比不变;随着进油压力的提升,峰值压力逐步增大,谷值压力不变,频率增大,增压比不变;随着喷嘴直径的增大,峰值压力逐步降低,谷值压力不变,频率增大,增压比逐步降低。同时,单周期瞬时压力中包含有两次主级脉动与一段次级脉动,通过调制进水压力可获取具有间断性与连续性的脉动压力特征。

高峰值功率GMN飞秒光纤激光器研究进展(特邀)

高峰值功率飞秒光纤激光器在高精度工业制造、生物医学、国防、航空航天等领域有着广泛的应用。目前,产生高峰值功率飞秒光纤激光的主要方法是啁啾脉冲放大技术和非线性脉冲放大技术,然而前者虽然能够产生单脉冲能量大于1 mJ的飞秒脉冲,但受限于增益窄化效应,产生的脉冲持续时间通常大于200 fs。后者虽然能够产生持续时间~50 fs的脉冲,但整体设计比较复杂,限制了其应用范围。随着国内外相关工作的长期积累以及激光器件等硬件能力的提升,科研人员提出了一种基于增益管理非线性(Gain-Managed Nonlinear,GMN)放大的方案,这项技术能够以简单的系统设计产生持续时间小于50 fs的脉冲,还能保证紧凑的系统结构。综述了增益管理非线性放大技术的理论研究进展,总结了国内外不同设计结构的增益管理非线性放大系统研究进展,最后对增益管理非线性放大系统的应用进行了展开分析,展望了其在未来的发展方向。进一步分析了泵浦波长、泵浦方式对增益管理非线性放大的影响,提出了一种全光纤一体化的增益管理非线性放大系统,并利用该系统进行了超连续谱产生的应用研究。

High-power femtosecond laser generation from an all-fiber linearly polarized chirped pulse amplifier

An all-fiber high-power linearly polarized chirped pulse amplification(CPA)system is experimentally demonstrated.Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fiber Bragg gratings(CFBGs),a maximum average output power of 612 W is achieved from a high-gain Yb-doped fiber that has a core diameter of 20μm with a slope efficiency of approximately 68%at the repetition rate of 80 MHz.At the maximum output power,the polarization degree is 92.5%and the M^(2)factor of the output beam quality is approximately 1.29;the slight performance degradations are attributed to the thermal effects in the main amplifier.By optimizing the B-integral of the amplifier and finely adjusting the higher-order dispersion of one of the CFBGs,the pulse width is compressed to 863 fs at the highest power with a compression efficiency of 72%,corresponding to a maximum compressed average power of 440.6 W,single pulse energy of 5.5μJ and peak power of about 4.67 MW.To the best of our knowledge,this is the highest average power of a femtosecond laser directly generated from an all-fiber linearly polarized CPA system.

L波段全国产化2.5 kW级脉冲模块设计

随着国防和民用技术的迅速发展,高性能的L波段脉冲模块成为雷达和通信领域的关键组件。文章介绍了一个全国产化的2.5 kW级L波段脉冲模块的设计流程。该模块采用先进的射频放大技术和脉冲形成网络设计,结合本土材料和工艺技术的优势,实现模块的高性能和低成本生产。仿真和实验验证表明,设计的模块满足了所有预期的技术参数,包括功率水平、脉冲宽度和效率,通过了严格的质量控制和可靠性评估。

Monolithic tapered Yb‑doped fber chirped pulse amplifer delivering 126μJ and 207 MW femtosecond laser with near difraction‑limited beam quality

In this work,a high-energy and high peak power chirped pulse amplifcation system with near difraction-limited beam quality based on tapered confned-doped fber(TCF)is experimentally demonstrated.The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250µm at the thin end and 56/400μm at the thick end.With a backward-pumping confguration,a maximum single pulse energy of 177.9μJ at a repetition rate of 504 kHz is realized,corresponding to an average power of 89.7 W.Through partially compensating for the accumulated nonlinear phase during the amplifcation process via adjusting the high order dispersion of the stretching chirped fber Bragg grating,the duration of the amplifed pulse is compressed to 401 fs with a pulse energy of 126.3μJ and a peak power of 207 MW,which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fber laser.At the highest energy,the polarization extinction ratio and the M2 factor were respectively measured to be~19 dB and 1.20.In addition,the corresponding intensity noise properties as well as the short-and long-term stability were also examined,verifying a stable operation of the system.It is believed that the demonstrated laser source could fnd important applications in,for example,advanced manufacturing and photomedicine.

Thulium-doped all-PM fiber chirped pulse amplifier delivering 314 W average power

A high-power all polarization-maintaining(PM) chirped pulse amplification(CPA) system operating in the 2.0 μm range is experimentally demonstrated.Large mode area(LMA) thulium-doped fiber(TDF) with a core/cladding diameter of25/400 μm is employed to construct the main amplifier.Through dedicated coiling and cooling of the LMA-TDF to manage the loss of the higher order mode and thermal effect,a maximum average power of 314 W with a slope efficiency of 52% and polarization extinction ratio of 20 dB is realized.The pulse duration is compressed to 283 fs with a grating pair,corresponding to a calculated peak power of 10.8 MW,considering the compression efficiency of 88% and the estimated Strehl ratio of 89%.Moreover,through characterizing the noise properties of the laser,an integrated relative intensity noise of 0.11% at 100 Hz-1 MHz is obtained at the maximum output power,whereas the laser timing jitter is degraded by the final amplifier from 318 to 410 fs at an integration frequency of 5 kHz to 1 MHz,owing to the self-phase modulation effect-induced spectrum broadening.The root-mean-square of long-term power fluctuation is tested to be0.6%,verifying the good stability of the laser operation.To the best of our knowledge,this is the highest average power of an ultrafast laser realized from an all-PM-fiber TDF-CPA system ever reported.

1 MHz,273 W掺镱棒状光纤啁啾脉冲放大系统

掺镱超快光纤激光器因光束质量好、输出功率高而被广泛应用于科学研究、工业加工、医疗诊断等领域.大模场面积的棒状光纤可以提供平均功率在百瓦量级的高能量飞秒脉冲输出,本文基于掺镱棒状光纤搭建了啁啾脉冲放大系统,详细研究脉冲输入功率对脉冲放大及压缩的影响.实验结果表明,在低放大功率下(<160 W)增大输入功率可提升放大效率且脉冲压缩质量基本不受影响;当放大功率进一步增大时,需选择合适的输入功率避免积累过量非线性相位.该啁啾脉冲放大系统可将20 W圆偏光输入放大至305 W,压缩后产生平均功率为273 W、能量为273μJ的264 fs脉冲,脉冲平均功率和峰值功率比Pedersen课题组(Pedersen M E,Johansen M M,Olesen A S,Michieletto M,Gaponenko M,Maack M D 2022 Opt.Lett,475172)结果约提升了一倍.

核脉冲信号的对数处理

对于能量相差较大的γ脉冲信号,如果应用线性放大器进行放大及后续处理需要较大的线性范围和较低的噪声,否则难以兼顾高能脉冲的抗饱和与低能脉冲的抗噪声。试制了一个非线性放大电路,利用三极管PN结的对数伏安特性将能量相差10倍的脉冲信号放大为幅值相差1倍左右的脉冲信号,在特定的情况下兼顾高低能γ信号的放大便于后续信号处理,测试了基于固定阈值脉宽TDC的对数信号处理,效果较好,可减少噪声干扰。

速度脉冲型近场地震作用下某混合减震结构动力响应特性研究

近断层地震动的速度脉冲效应对结构的抗震性能具有不利影响,我国规范对近场效应的考虑通过不同断层距的近场增大系数体现。以距离断裂带不足5km的某混合减震框架结构为工程背景,选取一组典型的速度脉冲型近场地震波,并用基于小波分析的识别方法进行验证,同时基于抗规选波方式考虑场地地震环境选取另一组地震波,在均满足有效持时、地震动加速度峰值、反应谱相似性的前提下,对比设防、罕遇地震下脉冲波和规范选波结构响应的差异。结果表明:速度脉冲型地震动对近断层减震项目的结构响应有一定的放大作用,设防地震下基底剪力增大系数约为1.07,罕遇地震下基底剪力增大系数约为1.18~1.19,罕遇地震下消能元件的耗能更充分,结构构件的塑性损伤进一步发展,放大作用较设防地震更为显著;对于短周期减震结构,当选波没有区分速度脉冲地震记录同时又按抗规乘以1.5的近场增大系数时,可能高估结构的响应。