与794nm飞秒激光精确同步的无直流背底的1064nm脉冲光的产生

基于非共线光参量放大(NOPA)，以宽带794nm飞秒激光的倍频光为抽运光，以连续的He-Ne激光为信号光，产生了与宽带794nm飞秒激光精确同步的无直流背底的1064nm的脉冲光.实验结果显示该1064nm的光脉冲可作为光参量啁啾脉冲放大系统的抽运激光链的种子光，从而实现用全光学方法实现OPCPA系统抽运光和信号光的精确同步.还将非共线光参量放大器置于经特殊设计的He-Ne激光腔内，也同样成功得到了无直流背底的1064nm的光脉冲.经一次光参量放大后所得到的1064nm光的光谱和空间啁啾特性与非共线光参量放大器置于He-Ne激光腔外时得到的1064nm的光脉冲相同，而其单脉冲能量约为腔外NOPA的10倍. 关键词： 非线性光参量放大 光参量啁啾脉冲放大 时间同步     

Lorenz系统驱动声光双稳时空混沌系统并行同步的研究

研究了一个时间混沌系统驱动多个时空混沌系统的并行同步问题.以单模激光Lorenz系统和一维耦合映像格子为例,在单模激光Lorenz系统中提取一个混沌序列,通过与一维耦合映像格子中的状态变量耦合使单模激光Lorenz系统和多个同结构一维耦合映像格子同时达到广义同步,并且多个一维耦合映像格子之间实现完全并行同步.通过计算条件Lyapunov指数,可以得到并行同步所需反馈系数的取值范围.数值模拟证明了此方法的可行性和有效性.     

上海深紫外自由电子激光装置中激光与束流的精确同步

介绍了一种基于相干辐射测量的激光-电子束同步方法,描述了实现空间及时间同步的基本原理、步骤和细节,并利用这种方法在上海深紫外自由电子激光装置（SDUV-FEL）上实现了电子束与激光之间亚ps量级的精确同步,为基于外种子激光的高增益高次谐波产生（HGHG）、回声型谐波产生（EEHG）和级联HGHG自由电子激光实验奠定了坚实的基础。还利用这种手段对不同条件下的电子束纵向特性进行了测量和分析。     

飞秒与皮秒激光脉冲的主动同步及和频产生宽带超短激光的研究

利用主动同步方式实现了飞秒钛宝石激光器与皮秒Nd:YVO₄激光器的同步，得到了时间抖动低于1ps的同步精度.在此基础上进行了两束激光的和频实验研究，产生了波长为460nm的宽带蓝光飞秒脉冲激光.这一技术不仅代表了实现不同波长、不同脉冲宽度激光同步的一般方法，而且也证明了通过和频、差频两束不同激光产生新波长超短脉冲激光的一种全新技术方案. 关键词： 主动同步 超短脉冲 和频 差频     

纳秒激光烧蚀冲量耦合数值模拟

为研究激光烧蚀靶产生冲量过程和机理, 建立了一个复杂的一维热传导和流体动力学模型. 以空间碎片常见材料Al为例, 用建立的模型数值计算了纳秒脉宽激光烧蚀靶产生的冲量及冲量耦合系数随时间变化情况. 数值结果和已有的实验数据符合的较好. 数值计算表明: 激光脉冲时间内, 靶获得的冲量随时间迅速增加, 在脉冲时间结束后, 冲量变化随时间趋于稳定; 在冲量耦合过程中, 烧蚀等离子体向真空膨胀, 羽流尺度逐渐增大, 同时吸收入射激光能量, 导致激光与靶耦合的能量降低. 关键词： 激光烧蚀 冲量耦合 等离子体     

短脉冲激光加工双温方程的优化运算

为研究双温方程中电子热传导项和电子与晶格耦合项对激光辐照物体表面温度场求解的影响,对这两项施加了约束条件。由于飞秒和亚皮秒激光与物质相互作用时间短,电子与晶格来不及耦合,所以对耦合项施加时间约束;根据相分离条件(CPPS),对热传导项施加空间约束。利用有限元方法建立了激光烧蚀金属铜膜表面的有限元模型。通过分析双温方程中热传导项和耦合项对计算结果的影响,发现短脉冲激光与铜金属相互作用过程中电子与晶格耦合项可以忽略,而传导项不可忽略。求解适当激光功率下的双温方程,得到了激光作用中心电子与晶格在不同脉冲宽度激光辐照下的温度变化关系。根据100 fs激光作用后晶格温度场的空间分布情况,研究了激光作用的相分离区域、相爆炸区域以及熔融区域的分布情况。     

基于液晶空间光调制器的太赫兹波频谱调制

频谱可调制的太赫兹波具有广泛的应用价值。利用一台纯相位式的液晶空间光调制器对飞秒激光脉冲进行空间整形,通过改变飞秒激光脉冲的横向空间分布,实现太赫兹波频谱的调制。在实验中,利用光泵浦整流方式产生太赫兹波,并利用太赫兹时域光谱系统对太赫兹信号进行探测。通过GS算法在液晶空间光调制器上加载不同的相位图,获得了不同的飞秒激光脉冲横向空间分布。通过改变探测距离和飞秒脉冲的空间分布参数,实现了太赫兹波频谱的调制。还利用菲涅尔衍射算法对这一过程进行了理论模拟,理论模拟结果与实验结果吻合的较好,这充分说明了基于飞秒脉冲空间整形的太赫兹光谱调制技术的可行性。     

用于宽带啁啾脉冲光参量放大系统精确同步的新方法

基于非共线光参量放大,以波长800 nm飞秒激光的倍频光为抽运光,以激光二极管640 nm连续波激光为信号光,产生了与800 nm飞秒激光精确同步的无直流本底的1064 nm脉冲光。实验结果显示该1064 nm的光脉冲在脉冲能量和空间光束质量上均可作为1064 nm波长脉冲放大器的种子光。仅通过一级简单紧凑的非共线参量放大就可实现光周期量级的光参量啁啾脉冲放大系统的抽运激光和种子光的精确同步。     

基于受激布里渊散射能量转移的冲击点火激光技术研究

提出一种新型的激光放大技术, 高效地实现冲击点火所需的10² ps级高功率激光脉冲. 该技术耦合了传统的激光驱动器放大技术和受激布里渊散射(SBS) 脉冲压缩技术, 在不改变现有激光装置主体结构的前提下, 使用长脉冲(数 ns) 充分提取主放大器储能, 然后在系统输出端通过SBS进行脉冲自抽运的能量转移, 将长脉冲能量转移给10² ps级的冲击脉冲, 实现高效放大的目的. 该技术在主动控制下实现能量转移, 将克服传统SBS压缩时间特性不可控的缺点, 输出满足冲击点火时域特性要求的精密控制激光脉冲.     

X射线条纹相机紫外光时标研究

 报导了一种采用超短紫外光脉冲作为X 射线条纹相机时标系统的方法。时标光脉冲来自用多模石英光纤耦合的波长为1.06μm 四倍频超短紫外光脉冲激光系统。时标光脉冲与打靶产生的X 射线均被X 射线条纹相机接收, 以用来测定激光打靶时X 射线产生的相对时间关系或相机之间同步的时间关系。实验得到通过光纤引导的时标光脉冲宽度约为30ps。     

The steady state of a particle in a vibrating box and possible application in short pulse generation of charged particles

In this paper the classical evolution of a particle is studied which bounces back and forth in a 1D vibrating cavity such that the reflection from the wall does not change the speed of the particle. A peculiar behaviour of the particle motion can be seen where the time evolution of the motion shows superposition of linear and oscillatory behaviour. In particular, the parameter range is found in which the particle oscillates between the walls in steady state as if the wall was static and it is showed that for these parameter ranges the particle settles to this steady state for all initial conditions. It is proposed that this phenomenon can be used to bunch charged particles in short pulses where the synchronization proposed in our model should work against the space charge effect in the charged particle bunch.     

Generation and time jitter of the loose soliton bunch in a passively mode-locked fiber laser

We report a regime of the loose soliton bunch in an erbium-doped passively mode-locked fiber laser. In this state,every soliton bunch consists of multiple pulses. The amount of multiple pulses inside the soliton bunch increase as the pump power rises. Moreover, the temporal average pulse-to-pulse separation decreases in general with the increase of the pump power. Further, the spatial-temporal sequences based on the dispersive Fourier transformation technique show that pulse-to-pulse interactions and time jitter can result in pulse forking inside the soliton bunch. Finally, we theoretically demonstrate the soliton bunch with different pulse-to-pulse separations.     

A simple method for timing an XFEL source to high-power lasers

We propose a technique for timing an X-ray free-electron laser (XFEL) to a high-power conventional laser with femtosecond accuracy, yielding the relative jitter between pump and X-ray probe, and allowing sorting of experimental results over a certain time window. The same electron bunch is used to produce both an XFEL pulse and an ultrashort optical pulse by means of an optical radiator downstream of the X-ray undulator. Being produced by the same electron bunch, these pulses are perfectly synchronized. Cross-correlation techniques will allow to determine relative jitter between the optical pulse (and, thus, the XFEL pulse) and a pulse from an external pump-laser. Technical realization of the proposed timing scheme uses an optical-replica synthesizer setup to be installed after the final bunch-compression stage of the XFEL for electron bunch diagnostics purposes. A number of critical issues are quantitatively analyzed.     

Simulation study of electron injection into plasma wake fields by colliding laser pulses using OOPIC

An electron injector concept for a laser-plasma accelerator has been developed which relies on the use of counter propagating ultrashort laser pulses. In this paper, we use OOPIC the fully self-consistent, twodimensional, particle-in-cell code to make a parameter study to determine the bunches that can be obtained through collisions of two collinear laser pulses in uniform plasma. A series of simulations show that one can obtain a short (<10fs) bunch with its charge of about 15pC, and energy spread of about 15%. We also discussed the variation of the transverse spot size of the electron bunch and found the bunch would undergo the betatron oscillations.     

Generation of femtosecond X-ray pulses via laser–electron beam interaction

The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.     

具有空间重叠性和时间同步性的双波长TEA CO2激光器研究

提出了一种改进的双波长TEA CO2激光器,不仅具有良好的空间重叠性,而且具有比较理想的时间同步性.该激光器由两个空间上部分重叠的光栅和一个锗镜构成光栅-平面腔,两个光栅前后放置,相互利用,共同建立双频振荡,由锗镜输出双波长激光.通过改变两光栅的有效面积,对两输出脉冲空间重叠性进行调节;通过改变两光栅的角度形成的失谐缩小输出脉冲的时间间隔,达到时间同步性.实验表明,可以在空间重叠性的基础上使两输出脉冲的时间间隔由1 000 ns调整到200 ns.     

Anticipating the response of excitable systems driven by random forcing

We study the regime of anticipated synchronization in unidirectionally coupled model neurons subject to a common external aperiodic forcing that makes their behavior unpredictable. We show numerically and by analog hardware electronic circuits that, under appropriate coupling conditions, the pulses fired by the slave neuron anticipate (i.e., predict) the pulses fired by the master neuron. This anticipated synchronization occurs even when the common external forcing is white noise.     

Experimental investigation of harmonic and subharmonic synchronization of 40 GHz mode-locked quantum-dash laser diodes

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.     

Optical-pulse frequency stabilization of self-mode-locked HeNe lasers

The production of optical pulses with very stable time delays is considered. The method is based upon phase synchronization of the pulse frequency of a self-mode-locked laser by means of an external generator with very high frequency stability. Experimental results are described, and new time and length standards are discussed.     

Anharmonic pulses due to transition radiation

The possibility of using the transition radiation of an electron bunch to generate nonstationary anharmonic pulses in free space and in a dispersive medium is demonstrated. It is shown that the transition radiation of the bunch gives rise to an infinite train of nonstationary anharmonic pulses described by solutions to the Klein-Gordon equation. The polarization of the resulting field at its leading edge appears to be different from the field polarization at the interface. The leading edge becomes steeper with time. It is shown that the bunch density longitudinal distribution and the parameters of the dispersive medium can be determined from the values of the fields and their derivatives near the leading edge of the resulting signal.