百太瓦级超短超强钛宝石激光装置

100TW级激光装置采用了全钛宝石的啁啾脉冲放大技术路线，可以输出3个不同功率段，以适应不同物理实验需求。前端系统是一个台面TW量级系统，主要包括钛宝石自锁模飞秒振荡器、Offner无像差展宽器、再生放大器、预放大器及主放大器。从前端系统主放输出的脉冲能量高达300mJ。为了克服再生放大器中的增益窄化效应及预补偿放大过程中引入的光谱振幅和位相畸变，在飞秒振荡器后应用一个可编程的声光色散滤波器（AOPDF）。AOPDF可以对脉冲光谱的振幅和位相进行主动的调制，补偿增益窄化效应及高阶色散引起的位相畸变。没有应用AOPDF进行预调制，则再生放大器输出的光谱宽度为25nm；当应用AOPDF进行适当调制后，再生放大输出的光谱宽度为40nm，因而最后的压缩脉冲可以获得更窄的压缩脉宽。     

可编程声光色散滤波器在10 Hz飞秒再生放大系统中的应用

报道了在10 Hz飞秒再生放大超快激光系统中,运用可编程声光色散滤波器(AOPDF)对注入再生放大的种子光进行频谱整形和色散预补偿,使钛宝石激光系统输出光脉冲谱线半峰全宽由原来的38 nm展宽到66 nm,压缩后输出脉冲宽度从35 fs减小到20 fs。实验结果表明,利用可编程声光色散滤波器能够同时独立进行光谱整形和大范围内色散补偿的特性,可以有效抑制啁啾脉冲放大过程中存在的谱线增益窄化效应,补偿钛宝石激光系统中存在的残留色散。这为进一步研制小于20 fs,10 TW量级钛宝石激光系统奠定了基础。     

采用光谱展宽技术的钛宝石飞秒激光放大器

报道了飞秒激光啁啾脉冲放大器中的激光脉冲光谱展宽技术，实验中使用了几种光谱展宽元件，结果表明使用激光光谱展宽元件能有效地将飞秒激光脉冲 光谱展宽，抑制了飞秒激光放大器中常见的激光脉冲光谱增益窄化现象，从飞秒放大系统的振荡级输出28fs种子脉冲，放大后得到了重复频率为10Hz、峰值功率为1．6TW、脉冲宽度37．5fs的超短强飞秒激光脉冲 。     

用于补偿增益窄化效应的Rugate滤波器设计

采用Rugate膜系理论，分别根据钛宝石和钕玻璃介质增益窄化的特点，合理选择补偿增益窄化的调制函数，优化设计出了分别用于补偿钛宝石系统和钕玻璃系统增益窄化效应的Rugate滤波器.由普通均匀多层膜的特征矩阵方法近似分析了设计出的Rugate滤波器的光谱响应，数值模拟了Rugate滤波器的光谱补偿效果.结果显示，能比较好的符合光谱补偿的要求，可以用作补偿增益窄化效应的光谱调制滤波器. 关键词： 超短脉冲 增益窄化 光谱补偿 Rugate滤波器     

Nd,Gd:SrF2晶体材料在宽带放大中的光谱增益特性

光谱的增益窄化是影响超短脉冲宽带放大的关键因素之一.本文利用Nd, Gd:SrF₂晶体发射光谱的特点,开展了宽带放大中的光谱增益特性理论和实验的研究.通过数值模拟,详细研究了激光增益介质在不同的光谱增益线型及不同增益倍数下,输出光谱的演化规律. Nd, Gd:SrF₂晶体光谱增益窄化特性研究实验结果表明,输入光谱半高宽为5 nm时,在140倍的增益条件下, Nd, Gd:SrF₂晶体的输出光谱宽度未见明显窄化,实验结果与理论计算分析相符合.研究结果为氟化物晶体在宽带啁啾脉冲放大的应用奠定了基础.     

多个超短脉冲相干叠加构成窄带平顶长脉冲的研究

利用超短脉冲放大过程中的光谱增益窄化效应以及标准具的滤波作用,提出了基于再生放大器的多脉冲相干叠加方案，并对该方案在多脉冲叠加阶段的工作原理进行了分析；在小信号增益区内，对多个超短脉冲相干叠加进行了理论分析和数值计算，数值模拟的结果表明，影响形成窄带平顶长脉冲的基本关系为子脉冲宽度、再生放大器中的损耗及其与振荡器的长度失配量对构成脉冲时间波形影响很大，而对其频谱影响很小；叠加脉冲个数、标准具的通带宽度对构成脉冲波形和光谱均有影响. 关键词： 超短脉冲 多脉冲叠加器 窄带平顶长脉冲 数值计算     

高功率超短脉冲激光系统中光谱增益窄化补偿的调制函数

 设计了一种与高功率超短脉冲激光放大过程中获得的总增益、增益介质的带宽、激光带宽、脉冲中心波长等参数相关的调制函数，对激光放大过程中的光谱增益窄化进行补偿。此调制函数的优越性在于，对不同性能的激光系统，无需改变调制函数的形式就能适用。通过数值模拟的方法，讨论了在不同增益介质带宽、激光带宽、脉冲中心波长下的补偿效果。此调制函数在高功率超短脉冲激光系统中有良好的应用前景。     

钛宝石超短脉冲放大过程中的增益窄化效应

本文研究超短脉冲的放大过程中产生的一个很重要的非线性效应──脉冲频谱的增益窄化效应(Gain Narrowing).分析了它的产生机理,同时指出了增益窄化效应在制约由于自相位调制效应引起的脉冲频谱展宽现象时所起的脉冲整形作用,得出了决定这种整形效果的种子脉冲参数和对放大器性能的要求.     

大型短脉冲激光装置中脉冲前沿畸变效应的研究

阐述了短脉冲激光装置中脉冲前沿畸变效应的产生机理和可能的畸变源.利用Fourier光学方法，建立了一个基于单程压缩构型的研究脉冲前沿畸变效应的理论模型，分析不同种脉冲前沿畸变效应对于压缩器输出脉冲的近场时空特性的影响.基于此,对一个在建的大口径（300 mm）短脉冲装置中的各种畸变源（包括可编程声光光谱色散滤波器、透镜色差以及劈板等元件）进行了数值计算.研究表明：近场输出脉冲宽度显著加宽，输出脉冲前沿形状不同于输入时的畸变形状，只有中心部分区域的脉冲前沿形状与输入类似，该区域的大小由系统带宽决定. 关键词： 脉冲前沿畸变 角色散 单程压缩 透镜     

紫外超短脉冲激光放大过程中脉宽压缩的方案设计

采用放电泵浦KrF准分子激光放大器放大波长为248.4nm的紫外超短脉冲激光。对于能量为0.7mJ、脉宽为550fs的输入脉冲,在光束直径保持10mm不变的条件下,能量放大到15mJ,脉宽展宽到1200fs。为了压缩输出脉冲宽度,分析了群速度色散和自相位调制效应对脉宽展宽的影响。利用棱镜对,采用4种不同的实验方案对脉冲引入负的线性频率啁啾,以补偿KrF准分子激光放大器CaF2窗镜中的群速度色散和自相位调制对脉冲引入的正的线性频率啁啾。结果表明:在放大器之前放置棱镜对的方式可以在保持输出脉冲能量为15mJ的同时,在棱镜对间距为110cm的条件下,将输出脉冲宽度压缩到370fs,输出波长为248.4nm、带宽为0.4nm。     

Generation of near transform-limited ultrashort laser pulses in kilohertz chirped-pulse amplification system by compensating high order phase distortions

The effects of gain narrowing and high order dispersions on the pulse duration in our kilohertz chirpedpulse amplification system have been compensated experimentally. Using an acousto-optic programmable dispersive filter (AOPDF), the spectral full-width at half-maximum (FWHM) is expanded from 30 to50 nm. Stable laser pulses with the duration of 30 fs (FWHM), which is 1.07 times Fourier-transformlimitation, have been acquired by pre-compensating the high order phase distortions using the phase measured by spectral phase interferometry for direct electric-field reconstruction (SPIDER).     

SILEX-I: 300-TW Ti:sapphire laser

Based on chirped pulse amplification technology, we have built a Ti:sapphire laser system, called SILEX-I (superintense laser for experiments on extremes), at CAEP, which consists of three stages with 5-, 30-, and 300-TW outputs, respectively. The first and the second stages work at 10 Hz, while the third works at single shot. Pulse durations of 30 fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) to compensate for the spectral gain narrowing in the regen. By taking a number of advanced measures for spatial beam control, such as spatial beam shaping, relay-imaged propagation, precise alignment of compressor gratings, and OAP, near-diffraction limited focal spots (FWHM) have been obtained. Focused intensities are calculated at (1–3) × 10²⁰ W/cm² with an f/2.2 OAP.SILEX-I has shown an excellent stability and reliability in operations for applications since its completion and will soon be able to operate at 500 TW.     

Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping

We demonstrate experimentally that an arbitrary phase and amplitude profile can be applied to an ultrashort pulse by use of an acousto-optic programmable dispersive filter (AOPDF). Our filter has a large group-delay range that extends over 3 ps and a 30% diffraction efficiency over 150 THz. Experiments were conducted on a kilohertz chirped-pulse amplification laser chain capable of generating 30-fs pulses without additional pulse shaping. Compensating for gain narrowing and residual phase errors with an AOPDF in place of the stretcher results in 17-fs transform-limited pulses. Arbitrary shaping of these 17-fs pulses is also demonstrated in both the temporal and the spectral domains.     

空气中激光等离子体通道的三次谐波光谱特性研究

对不同条件下强激光在空气中形成等离子体通道的三次谐波光谱特性进行了研究。单脉冲能量12mJ,脉宽30 fs,重复频率10 Hz,中心波长795 nm的飞秒激光脉冲经0.5 m焦距的凹面镜聚焦,在空气中形成了等离子体通道,并在前向观测到谱线半峰全宽(FWHM)为15 nm的三次谐波。随着脉冲啁啾的变化,三次谐波的光谱出现红移或兰移,当激光脉冲附带 1.3×105fs2的二阶色散时,三次谐波谱线红移且谱峰强度增长了两倍。同时,通过改变可编程声光色散滤波器(AOPDF)光谱调制的位置(Hole position),三次谐波的光谱也发生频移。     

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.     

Spectral mirror for ultra-short, high peak power, multi-PW Ti:sapphire lasers

A multilayer mirror for spectral filtering adapted to ultra-short and multi-PW Ti:Sa laser has been designed, manufactured and characterized. The method used to determine both the reflectivity shape and the coating design leads to global compensation of gain narrowing, saturation and spectral phase. The result is a spectral control on 200 nm range while keeping a flat spectral phase. This kind of filter will enable obtaining 15 fs pulse duration for multi-PW laser systems based on Ti:Sa.     

Pulse Compression by Filamentation in Argon with an Acoustic Optical Programmable Dispersive Filter for Predispersion Compensation

We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.     

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.     

Active spectral phase control by use of an acousto-optic programmable filter in high-repetition-rate sub-80 fs nonlinear fiber amplifiers

We report the generation of sub-80 fs pulses with energy in the 100 nJ range at 1050 nm and a repetition rate up to 164 kHz based on a nonlinear fiber amplification system combined with an active control of the spectral phase. This control is performed by an acousto-optic programmable dispersive filter operated at a multiple of its acoustic repetition rate. This result opens up its possible use in highly nonlinear fiber chirped-pulse amplification setups.