Controlling the carrier-envelope phase of ultrashort light pulses with optical parametric amplifiers

The phase link between signal, idler, and pump waves in a parametric interaction allows generation of an idler pulse with a phase independent of that of the input pulse. We suggest the use of a white-light seeded optical parametric amplifier as a self-stabilized source of few-cycle pulses, in which the phase of the electric field is exactly reproduced in each laser shot.     

Interaction of intense ultrashort laser pulse with shell target

Based on numerical PIC modeling and an analytical model, we analyze the interaction of a short high-intensity laser pulse with homo- and heterogeneous (two-layer) shell targets. We show that the shell target is capable of focusing ions in a narrow region. In this case, the ion energy exceeds the ion energy for a flat infinite target of the same thickness. We propose to use the effect of focusing and cumulation of ions to implement the collision of ionic beams that counterpropagate from opposite sides of the sphere and to increase the yield of ion-ion reactions. The constructed model makes it possible to calculate the energy of the ion and the number of ions in the region of focusing.     

Long-term passive stabilization of the carrier-envelope phase of an intense infrared few-cycle pulse source

We present long-term stability of the carrier-envelope phase of intense infrared few-cycle pulses at 1.6 μm, generated by optical parametric chirped-pulse amplification. The employed system is based on a passive stabilization scheme that obviates the need for active feedback loops, and requires only control of environmental parameters. The stabilization is demonstrated to last for up to 45 h, during which the carrier-envelope phase drift is measured to be less than \(250\,\text{mrad}\) . This marks, to the best of our knowledge, the longest demonstrated phase-stable operation of a passively stabilized, amplified few-cycle source to date.     

Controlling Rydberg excitation process with shaped intense ultrashort laser pulses

We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses. By numerically solving the time-dependent Schr?dinger equation(TDSE), we systematically study the dependence of the population of the Rydberg states on the π phase step position in the frequency spectra of the laser pulse for different intensities, central wavelengths and pulse durations. Our results show that the Rydberg excitation process can be effectively modulated using shaped intense laser pulses with the laser intensity as high as 1 × 10~(14) W/cm~2. Our work also have benefit to the future investigation to find out the dominant mechanism behind the excitation of Rydberg states in strong laser fields.     

On self-focusing of an ultrashort intense relativistic laser pulse in a plasma

The development of the spatiotemporal (filamentation) instability of a laser pulse upon excitation of a plasma wave is studied numerically and analytically. It is shown that first, as in a medium with inertialless cubic nonlinearity, the filamentation of radiation occurs and then filaments are attracted to each other. The following evolution differs weakly from the evolution of a smoothed wave beam in a medium with inertial nonlinear response.     

超短超强激光实验伴生电磁脉冲的模拟研究

靶室腔体谐振产生的电磁辐射是超短超强激光与靶相互作用实验中生成的电磁脉冲(EMP)来源之一。基于有限元分析方法,对靶室腔谐振产生电磁脉冲和电磁脉冲通过窗口向外传播这两个过程进行仿真模拟。前者模拟获得空腔和含结构模型谐振时特征磁场,结果显示内部结构对电磁场强度分布和谐振频率有显著影响;后者模拟结果显示,窗口外侧电场强度比窗口内侧高约40%,而且电磁脉冲传播到靶室外后呈球面波形式扩散并衰减。对电磁脉冲的强度衰减规律进行了分析,得到该衰减曲线的拟合函数。     

啁啾脉冲对氢分子离子解离动力学的影响

本文通过数值求解一维含时薛定谔方程,理论研究了超短啁啾脉冲（5-fs,790-nm）对处于低振动态氢分子离子解离动力学的影响. 研究过程中有效利用流算符的方法得到不同激光强度下的解离几率及核波包密度分布. 结果表明：低强度的啁啾脉冲可显著增强低振动态氢分子离子的解离过程,使解离过程提前发生并在较短的时间内获得较多的解离产物, 并给出相应的理论解释.     

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subelusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the ease of homonuelear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuelear clusters with larger sizes are required to achieve a greater neutron yield.     

超短强激光脉冲激励甲烷团簇的内电离机理

采用三维粒子动力学模拟方法研究了甲烷团簇在超短强激光脉冲激励下的爆炸动力学行为,重点讨论了几种典型的内电离机理对团簇爆炸过程中离子的价态和动能的影响.研究表明,在激光脉冲强度比较小的情况下,团簇中的原子主要是在光场作用下通过隧道电离的方式发生电离.当激光场进一步增强时,势垒压低电离是电离的主要方式.在相同的较高激光强度下,团簇更容易通过势垒压低电离达到高的电离价态.团簇发生电离后,其内部库仑电场的点火电离效应和内部滞留自由电子的碰撞电离效应也将增强团簇的再次电离过程. 关键词： 超短强激光脉冲 甲烷团簇 内电离     

近共振区超短强激光脉冲激发的等离子体尾波场

用一维相对论粒子模拟研究了相对论超短强激光脉冲在等离子体中传播时激发的尾波场,初步获得了近共振区尾波场的峰值幅度随激光脉冲宽度变化的特点,发现在近共振区等离子体波激发出现增强。通过准静态近似下尾波激发的一维非线性方程数值求解,并与粒子模拟结果比较,得到了该非线性方程的适用范围：当激光脉冲宽度小于等离子体波波长的4倍时,该方程所得结果与粒子模拟结果一致;而当激光脉冲宽度大于该数值时,该方程不再适用。     

近共振区超短强激光脉冲激发的等离子体尾波场

 用一维相对论粒子模拟研究了相对论超短强激光脉冲在等离子体中传播时激发的尾波场,初步获得了近共振区尾波场的峰值幅度随激光脉冲宽度变化的特点,发现在近共振区等离子体波激发出现增强。通过准静态近似下尾波激发的一维非线性方程数值求解,并与粒子模拟结果比较,得到了该非线性方程的适用范围：当激光脉冲宽度小于等离子体波波长的4倍时,该方程所得结果与粒子模拟结果一致;而当激光脉冲宽度大于该数值时,该方程不再适用。     

Improved carrier-envelope phase locking of intense few-cycle laser pulses using above-threshold ionization

A robust nonoptical carrier-envelope phase (CEP) locking feedback loop, which utilizes a measurement of the left-right asymmetry in the above-threshold ionization (ATI) of Xe, is implemented, resulting in a significant improvement over the standard slow-loop f-to-2f technique. This technique utilizes the floating average of a real-time, every-single-shot CEP measurement to stabilize the CEP of few-cycle laser pulses generated by a standard Ti:sapphire chirped-pulse amplified laser system using a hollow-core fiber and chirped mirror compression scheme. With this typical commercially available laser system and the stereographic ATI method, we are able to improve short-term (minutes) CEP stability after a hollow-core fiber from 450 to 290 mrad rms and long-term (hours) stability from 480 to 370 mrad rms.     

Precise, real-time, every-single-shot, carrier-envelope phase measurement of ultrashort laser pulses

In this Letter we demonstrate a method for real-time determination of the carrier-envelope phase of each and every single ultrashort laser pulse at kilohertz repetition rates. The technique expands upon the recent work of Wittmann and incorporates a stereographic above-threshold laser-induced ionization measurement and electronics optimized to produce a signal corresponding to the carrier-envelope phase within microseconds of the laser interaction, thereby facilitating data-tagging and feedback applications. We achieve a precision of 113 mrad (6.5°) over the entire 2π range.     

All optical electron injector using an intense ultrashort pulse laser and a solid wire target

Energetic electron bunches were generated by irradiating a solid tungsten wire 13 μm wide with 50 femtosecond pulses at an intensity of ∼3×10¹⁸ W/cm². The electron yield, energy spectrum and angular distribution were measured. These energetic electron bunches are suitable for injection into a laser driven plasma accelerator. An all-optical electron injector based on this approach could simplify timing and alignment in future laser-plasma accelerator experiments. PACS 41.75.Ht; 41.75.Lx; 52.38.Kd; 52.38.Ph     

Angular distributions for double ionization of Li- by an ultrashort, intense laser pulse.

We predict photoelectron angular distributions for double ionization of Li- by both weak and intense ultrashort, linearly polarized laser pulses by direct numerical integration of the three-dimensional, time-dependent Schr?dinger equation. Li- is treated as a two-active electron system. Near threshold, for low intensity we recover general features of angular distributions for one-photon double ionization. For the intense field (multiphoton) case, the photoelectron angular distribution changes significantly, particularly in directions parallel and perpendicular to the laser polarization axis.     

Momentum distributions of ne(n+) ions created by an intense ultrashort laser pulse

Vector momentum distributions of Ne(n+) (n = 1,2,3) ions created by 30 fs, approximately 1 PW/cm(2) laser pulses at 795 nm have been measured using recoil-ion momentum spectroscopy. Distinct maxima along the light polarization axis are observed at 4.0 and 7.5 a.u. for Ne2+ and Ne3+ production, respectively. Hence, mechanisms based on an instantaneous release of two (or more) electrons can be ruled out as a dominant contribution to nonsequential strong-field multiple ionization. The positions of the maxima are in accord with kinematical constraints set by the classical "rescattering model."     

Complex dynamics of correlated electrons in molecular double ionization by an ultrashort intense laser pulse

With a semiclassical quasistatic model we achieve insight into the complex dynamics of two correlated electrons under the combined influence of a two-center Coulomb potential and an intense laser field. The model calculation is able to reproduce experimental data of nitrogen molecules for a wide range of laser intensities from the tunneling to the over-the-barrier regime, and predicts a significant alignment effect on the ratio of double over single ion yield. The classical trajectory analysis allows us to unveil subcycle molecular double ionization dynamics.     

Electronic and nuclear responses of fixed-in-space H2S to ultrashort intense laser fields

The Coulomb explosion dynamics of H2S, H2S3+-->H+ +S+ + H+, in ultrashort intense laser fields (12 fs, approximately 2 x 10(14) W/cm2) is studied by the coincidence momentum imaging of the three fragment ions. Different electronic and nuclear responses are identified depending on the direction of laser polarization epsilon in the molecular frame. The dependence can be interpreted in terms of the electronic and bonding characters of charge transfer states of H2S coupled to the electronic ground state.     

Dissociation and ionization of H+2 by ultrashort intense laser pulses probed by coincidence 3D momentum imaging

Laser-induced dissociation and ionization of H(+)(2) were simultaneously measured using coincidence 3D momentum imaging, allowing direct separation of the two processes, even where the fragment kinetic energy is the same for both processes. The results for 45 and 135 fs 790 nm pulses with an intensity of approximately 2.5 x 10(14) W/cm(2) differ from each other much more than one would expect from previous measurements with longer pulses. Ionization was negligible for the longer pulse and was strongly aligned along the laser polarization for the shorter pulse, but showed no structure in its kinetic energy distribution. In addition, the ionization to dissociation ratio was found to be much smaller than theoretically predicted for H(+)(2).