Compton Scattering of Attosecond X-Ray Pulses on a Hydrogen Atom

The Compton scattering of attosecond X-ray pulses on a hydrogen atom has been studied theoretically in terms of the spectral angular scattering probability during the action of a pulse. The dependence of scattering on the carrier frequency, pulse duration, and scattering angle has been analyzed. It has been shown that the probability of the process at certain parameters of the problem is a nonlinear function of the pulse duration.     

Broadband-Isolated Attosecond Pulse Generation by Two-Color Elliptically Polarized Laser Pulses

We numerically solve the two-dimensional Schrödinger equation and investigate isolated attosecond pulse generation by combining a left and a right elliptically polarized pulse together. It is found that the plateau of the harmonic spectra can be extended and the quantum paths can be controlled by adjusting ellipticity. A broadband width of about 220 eV is generated for the case that ellipticity equals 0.3, and time-frequency time–frequency analysis shows that only one long quantum path contributes to high-order harmonic generation. By superposing a bandwidth of 60 eV near the cutoff of the harmonic plateau, an attosecond pulse with the duration of about 62 as could be generated.     

飞秒超短脉冲激光加热金属平面靶

从能流分析出发,对飞秒超短脉冲激光与金属平面靶相互作用的机制进行了理论研究,对其中主要物理过程的能流损耗作了详尽的分析,并根据一维,双温热扩散模型推导了自由电子温度随时间变化的函数关系.并从理论上推导了超短脉冲近似假设成立的脉宽范围和在此条件下自由电子所能达到的最高温度表达式.     

Double Ionization Dynamics of Molecular Hydrogen in Ultrashort Intense Laser Fields

We experimentally investigate the double ionization of molecular hydrogen subjected to ultrashort intense laser pulses.The total kinetic energy release of the two coincident H~+ ions,which provides a diagnosis of different processes to double ionization of H_2,is measured for two different pulse durations,i.e.,25 and 5fs,and various laser intensities.It is found that,for the long pulse duration(i.e.,25 fs),the double ionization occurs mainly via two processes,i.e.,the charge resonance enhanced ionization and recollision-induced double ionization.Moreover,the contributions from these two processes can be significantly modulated by changing the laser intensity.In contrast,for a few-cycle pulse of 5fs,only the recollsion-induced double ionization survives,and in particular,this process could be solely induced by the first-return recollision at appropriate laser intensities,providing an efficient way to probe the sub-laser-cycle molecular dynamics.     

Ultrafast Electronic and Molecular Dynamics Induced by Ultrashort FEL Pulses

In recent years, short wavelength free electron lasers (FELs) have opened up access to ultrafast electronic and structural dynamics in matter. Currently, four FEL facilities are in operation in the world. FLASH [1 W. Ackermann, Nat. Photonics 1, 336 (2007).[Crossref], [Web of Science ®] , [Google Scholar]] in Germany and FERMI [2 P. Emma, Nat. Photonics 4, 641 (2010).[Crossref], [Web of Science ®] , [Google Scholar]] in Italy cover the range from extreme ultraviolet (EUV) to soft X-rays, while LCLS [3 T. Ishikawa, Nat. Photonics 6, 540 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] in the U.S. and SACLA [4 E. Allaria, Nat. Photonics 6, 699 (2012).[Crossref], [Web of Science ®] , [Google Scholar]] in Japan provide pulses in the hard X-ray regime. In addition, an upgrade version of SCSS [5 T. Shintake, Nat. Photonics 2, 555 (2008).[Crossref], [Web of Science ®] , [Google Scholar]], nicknamed SCSS+, has also just started user operation as a beamline of SACLA [6 See http://xfel.riken.jp/eng/users/index.html [Google Scholar]]. These FELs deliver coherent pulses combining unprecedented power densities up to ~10²⁰ W/cm² and extremely short pulse durations down to a few femtoseconds. The intense coherent FEL pulse focused down to ~1 μm² makes single-shot diffractive imaging of nano-crystals or even non-crystallized bio-samples as well as other small objects a reality. Time-resolved spectroscopic and structural studies on the timescale of femtoseconds, having FEL pulses as a probe, allow us to probe electrons and atoms in action. Additionally, since FEL pulses are in a new regime of intensity, they are opening up new research fields that exploit the interaction between intense short wavelength pulses and matter, leading to matter at extremely high energy. Relevant theories dealing with such extreme conditions are also rapidly growing.     

超短激光脉冲中时空耦合效应的研究进展

概述了超短激光脉冲中时空耦合效应的研究进展。将时空耦合效应分为一阶时空耦合和高阶时空耦合两大类,并详细介绍了两类时空耦合效应的研究历史和现状。其中一阶时空耦合效应相对较为简单,对其的理论及实验研究也较为充分。相比一阶时空耦合效应,高阶时空耦合效应的起源更广泛、种类更丰富、时空结构更复杂。目前,对高阶时空耦合效应的研究也刚处于起步阶段。最后,展望了该领域的研究趋势。     

超短激光脉冲在水中的非线性传输特性研究

基于扩展的非线性薛定谔方程及与其耦合的电子密度演化方程,理论研究了超短激光强脉冲在水中的非线性传输特性.理论模型综合考虑了衍射、正常群速度色散,多光子吸收、自聚焦及激光诱导产生的等离子体对光脉冲的自散焦效应.采用有限差分法模拟得到超短脉冲在传输过程中轴向上光功密度和等离子体密度的时空分布.系统分析了超短脉冲在水中传输的动力学过程,讨论了非线性自聚焦和等离子体自散焦效应在脉冲传输过程中的竞争关系.同时研究了不同入射激光能量,脉宽和聚焦条件对等离子体丝的时宅结构和脉冲能流横向分布的影响.该研究将有助于理解和推动超短光脉冲在激光医学、激光安全防护和水中激光加工中的应用.     

Resonant Auger Scattering by Attosecond X-Ray Pulses

As x-ray probe pulses approach the subfemtosecond range, conventional x-ray photoelectron spectroscopy(XPS) is expected to experience a reduction in spectral resolution due to the effects of the pulse broadening.However, in the case of resonant x-ray photoemission, also known as resonant Auger scattering(RAS), the spectroscopic technique maintains spectral resolution when an x-ray pulse is precisely tuned to a core-excited state. We present theoretical simulations of XPS and RAS spectra on a sho...     

强阿秒XUV激光脉冲下H_2+分子光电子能谱角分布非对称性

利用2D平面模型,求解了描述定向H_{_2}⁺分子和阿秒XUV脉冲相互作用的薛定谔方程,并求得光电子的角度分布．在计算模型中,采用基态1sσ_g和第一激发态2pσ_u的等比例混合态作为初始态,而激光脉冲的光子能量大于电离势,强度为10¹⁴ W/cm²． 计算结果表明,光电子角分布的非对称性和脉冲的宽度密切相关．这种非对称性实际上是由于初始态的基态和激发态的相干振荡而导致的．当使用长脉冲时,这种相干振荡的周期效应就会被平均而消失,从而产生的光电子能谱会呈对称角分布．     

Elastic Scattering of Ultrashort Laser Pulses on Noble Gas Atoms

Russian Physics Journal - The work deals with a theoretical investigation of elastic scattering of ultrashort electromagnetic pulses (USP) on the noble gas atoms in the far ultra-violet and soft...     

超短脉冲激光照射下光栅Talbot效应的实验研究

理论上研究了超短脉冲激光照射下光栅的Talbot效应,得到了超短脉冲激光照射下光栅Talbot图像的性质.实验上采用严格的实验方法(频率分辨光学开关装置测量超短脉冲激光、反射式扩束系统对超短脉冲进行扩束)很好地验证了理论分析结果.理论分析和实验结果表明,超短脉冲激光照射下光栅的Talbot图像的对比度会显著下降,而且超短脉冲激光的脉宽越短,Talbot距离越大,Talbot图像的对比度会进一步下降.     

On the Theory of Hydrogen Atom Ionization by Ultra‐Short Electromagnetic Pulses

An investigation of the probability of hydrogen atom ionization by ultra‐short electromagnetic pulses is carried out in the frame of perturbation theory We consider the case when the electric field strength amplitude E₀ in a pulse by two orders lower than characteristic atomic field strength E_a (E_a ? 5.1 · 10⁹ V/cm). A detailed investigation of the dependence of the probabilities on the pulse duration was performed for Gaussian pulse shapes. In the case where the carrier frequency of the Gaussian pulse is larger than the atomic ionization potential, the probability goes to the standard limit of perturbation per unit time. At the same pulse durations, the probabilities for carrier frequencies less than the ionization potential go to zero. The frequency dependence of the ionization probability becomes equal to the standard threshold dependence with increasing pulse duration time. A comparison between the ionization effects caused by wavelet pulses without carrier frequency and Gaussian pulses with carrier frequency shows that the same ionization probability values are achieved when the pulse carrier frequency is detuned by about 20% from the ionization threshold. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Silicon Ablation by Single Ultrashort Laser Pulses of Variable Width in Air and Water

The ablation of silicon by single laser pulses of variable width (0.3–9.5 ps) with a wavelength of 515 nm has been comparatively studied in air and water. A nonmonotonic behavior of ablation thresholds with a minimum at 1.6 ps, which is due to achieving the thermalization time of the electron and ion subsystems in silicon, has been revealed. It has been shown that, with an increase in the pulse width in the considered width range, the efficiency of the ablation of silicon decreases by a factor of 2.5 in air and increases by a factor of 2 in water. This behavior of ablation in air is attributed to a partial transition from phase explosion to surface evaporation, which is suppressed in water.     

Energetic Protons Emitted from Coulomb Explosion Dynamics of Large-Sized Hydrogen Clusters Driven by an Ultrashort Intense Laser Pulse

Protons with very high kinetic energy of about lOkeV and the saturation effect of proton energy for laser intensity have been observed in the interaction of an ultrashort intense laser pulse with large-sized hydrogen dusters. Including the cluster-size distribution as well as the laser-intensity distribution on the focus spot, the theoretical calculations based on a simplified Coulomb explosion model have been compared with our experimental measurements, which are in good agreement with each other.     

Selective Alignment of D2 Induced by Two Ultrashort Laser Pulses

通过求解D₂分子在飞秒激光场中的含时薛定谔方程,研究了室温下D₂分子在超快飞秒激光驱动下的的转动波包动力学. 选择用第一束超短飞秒脉冲与温度为300 K的D₂分子系综相互作用产生一个相干转动波包,用第二束超短飞秒脉冲在波包的1/4和3/4恢复周期选择操纵D₂分子取向. 研究结果表明,通过选择两束超短飞秒脉冲的延迟时间,可以有效控制D₂分子转动波包中奇偶态的相对布居,从而选择性的控制D₂分子取向.     

Polarization-selective Excitation of Dye Luminescence on a Gold Film by Structured Ultrashort Laser Pulses

Donut-shaped visible (515 nm) femtosecond laser pulses with linear, radial and azimuthal polarizations after tight focusing (numerical aperture NA = 0.65) have been used for spectrally adjusted excitation of plasmonenhanced rhodamine 6G dye luminescence on the surface of a nanocrystalline 45-nm thick gold film with its plasmon resonance near the laser line. Significant luminescence output increments—1.7-fold for radial polarization compared to the azimuthal one, and almost 3-fold—compared to the linear one, have been observed. This effect is related to significant transformation of the transverse electrical field component into longitudinal one for radial polarization (up to 33% in intensity, according to our calculations), and corresponding increase in excitation efficiency of plasmons in the smaller nanocrystallites throughout the film.     

含自频移啁啾超短脉冲间相互作用的数值研究

采用拟解法给出了Ginzberg—Landau方程类孤波解的参数表达式.通过数值模拟对啁啾超短脉冲间的相互作用进行了研究．结果表明, 随着相邻孤子间距离的减小,它们之间的相互作用变得越来越严重．传统的不等振幅法在一定程度上可以抑制孤子间的相互作用,通过选取合适的振幅比,找到了相邻孤子间相互作用平衡的最小距离,这对提高光纤传输的比特率具有十分重要的意义．讨论了多孤子间的相互作用,找到了抑制四孤子之间相互作用的合适振幅比．