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．     

Formation of Intense Attosecond Pulses in the Sequence of a Resonant Absorber and Active Medium of a Plasma-Based X-Ray Laser Modulated by an Optical Field

Radiophysics and Quantum Electronics - We study the possibility of transforming quasi-monochromatic seeding X-ray radiation into an attosecond pulse train in the system composed of a resonant...     

Controlling Population Transfer and Dissociation Rate of Na2 Molecules with Ultra-Short Intense Laser Pulses

A scheme used for controlling the population transfer and the dissociation rate of Na2 molecules is described by using the quantum wavepacket dynamical method. It is theoretically shown that the population transfer and the dissociation rate of Na2 molecules can be controlled by pump and probe laser pulses with appropriate widths of pulses, sequence and intensities.     

Above-Threshold Ionization of Xenon by Chirped Intense Laser Pulses

We experimentally investigate above-threshold ionization of xenon subject to chirped intense laser pulses. While for few-cycle laser pulses free of chirp, the Freeman resonance narrow peaks in the photoelectron spectra become strongly suppressed, they will re-emerge for laser pulses with a certain chirp. Moreover, the position of the resonant peaks exhibits a strong dependence on the direction of the chirp. The experimental features can be understood by a two-step ionization process; that is, a multi-photon excitation plus subsequent ionization process.     

Intense Terahertz Pulses from SLAC Linac Beams

The terahertz (THz) region of the electromagnetic spectrum spans frequencies roughly from 300 GHz to 20 THz, corresponding to wavelengths from 1 mm to 15 μm. Although this range overlaps the vibrational levels of many materials (for example, phonon modes of semiconductors), difficulties in developing adequate sources have slowed its exploitation, despite promising applications in imaging, chemistry, biology, and materials science. Recent progress in sources driven by both lasers and electron beams has started to fill this “terahertz gap.” Accelerator-based sources are now opening a new high-field regime with the potential to control materials with THz radiation by resonantly driving bonds, biasing a material with ultrashort electric or magnetic fields, or using the light as a catalyst. Some new sources can produce pulsed fields of sufficient intensity to drive nonlinear responses in matter.     

Vibrational Dynamics Studies by Nuclear Resonant Inelastic X-Ray Scattering

Nuclear resonant inelastic X-ray scattering of synchrotron radiation is being applied to ever widening areas ranging from geophysics to biophysics and materials science. Since its first demonstration in 1995 using the ⁵⁷Fe resonance, the technique has now been applied to materials containing ⁸³Kr, ¹⁵¹Eu, ¹¹⁹Sn, and ¹⁶¹Dy isotopes. The energy resolution has been reduced to under a millielectronvolt. This, in turn, has enabled new types of measurements like Debye velocity of sound, as well as the study of origins of non-Debye behavior in presence of other low-energy excitations. The effect of atomic disorder on phonon density of states has been studied in detail. The flux increase due to the improved X-ray sources, crystal monochromators, and time-resolved detectors has been exploited for reducing sample sizes to nano-gram levels, or using samples with dilute resonant nuclei like myoglobin, or even monolayers. Incorporation of micro-focusing optics to the existing experimental setup enables experiments under high pressure using diamond-anvil cells. In this article, we will review these developments. This revised version was published online in August 2006 with corrections to the Cover Date.     

X射线皮秒分幅相机在强X射线情况下的应用研究

扫描型变象管Ｘ射线皮秒分幅相机在强Ｘ射线情况下，由于空间电荷效应，像质变坏，甚至无法工作。本文简述了ＭｇＦ光阴极材料的性能。首次在Ｘ射线皮秒变象管分幅相机上的应用结果：降低了强Ｘ射线源情况下分幅管内空间电荷效应的影响，并获得了清晰的物理图像。     

Dielectric Detector of Intense X-Ray Radiation Fluxes

Physics of Atomic Nuclei - The high sensitivity of traditional diagnostic methods hinders their application in inertial confinement fusion with the pulsed radiation power of target plasma being as...     

Time Dependence of Resonant Photoprocesses Induced by Electromagnetic Pulses with Various Durations

Journal of Experimental and Theoretical Physics - We consider the motion of a classical electron in the field of a monochromatic plane wave of an arbitrary (linear, circular, or elliptic)...     

Generation of an Attosecond Pulse in Helium Excited by Half-Cycle X-Ray Pulses

Optics and Spectroscopy - Conventionally, attosecond pulses are obtained using generation of high-order optical harmonics upon excitation of various media by femtosecond laser pulses with the...     

Resonant Scattering of Picosecond Laser Pulses by Atoms in Alkali Metal Vapors

Resonant scattering of ultrashort laser pulses (ULPs) in the vicinity of spectral doublets in monatomic lithium and sodium vapors is studied theoretically. The scattering probability over the entire time of pulse action is calculated as a function of various parameters of the problem (carrier frequency and ULP duration, as well as vapor pressure and temperature). It is shown that the dependence of the total scattering probability on the pulse duration is generally nonlinear by nature.     

Generation of Intense Sub-10 fs Pulses at 385 nm

We demonstrated the generation and characterization of 9.7 fs, 180 J pulses centered at 385 nm via the frequency doubling of few-cycle near-infrared pulses. Both moderate conversion efficiency(9.5%) and broad phase matching bandwidth(20 nm) were achieved by shaping the spectra of the fundamental pulses. The strong intensity dependence of second-order harmonic generation and well controlled material dispersion ensured the inexistence of satellite pulses, which was confirmed by the self-diffractio...     

Threshold Effect in the Photoemission of Composite Nanoantennas Irradiated by Intense Femtosecond Laser Pulses

JETP Letters - A new mechanism has been proposed for the formation of energy spectra of photoelectrons by above-threshold photoemission of composite nanoantennas with small gaps between elements...     

Transform-Limited Pulses Are Not Optimal for Resonant Multiphoton Transitions

Maximizing nonlinear light-matter interactions is a primary motive for compressing laser pulses to achieve ultrashort transform limited pulses. Here we show how, by appropriately shaping the pulses, resonant multiphoton transitions can be enhanced significantly beyond the level achieved by maximizing the pulse's peak intensity. We demonstrate the counterintuitive nature of this effect with an experiment in a resonant two-photon absorption, in which, by selectively removing certain spectral bands, the peak intensity of the pulse is reduced by a factor of 40, yet the absorption rate is doubled. Furthermore, by suitably designing the spectral phase of the pulse, we increase the absorption rate by a factor of 7.     

Ionization of Clusters in Intense Laser Pulses through Collective Electron Dynamics

The motion of electrons and ions in medium-sized rare gas clusters ( approximately 1000 atoms) exposed to intense laser pulses is studied microscopically by means of classical molecular dynamics using a hierarchical tree code. Pulse parameters for optimum ionization are found to be wavelength dependent. This resonant behavior is traced back to a collective electron oscillation inside the charged cluster. It is shown that this dynamics can be well described by a driven and damped harmonic oscillator allowing for a clear discrimination against other energy absorption mechanisms.