Interesting Features of Ionization Potentials for Elements(Z≤119)along the Periodic Table

The ionization potential （IP） is a basic property of an atom, which has many applications such as in element analysis. With the Dirac-Slater methods （i.e., mean field theory）, IPs of all occupied orbitals for elements with atomic number （Z ≤ 119） are calculated conveniently and systematically. Compared with available experimental measurements, the theoretical accuracies of IPs for various occupied orbitals are ascertained. The map of the inner orbital IPs with Mood accuracies should be useful to select x-ray energies for element analysis. Based on systematic variations of the first IPs for the outermost orbitals in good agreement with experimental values as well as other IPs, mechanisms of electronic configurations of all atomic elements （Z ≤ 119） along the periodic table are elucidated. It is interesting to note that there exist some deficiencies of the intermediate orbital IPs, which are due to electron correlations and should be treated beyond the mean field theory.

Application of multi-pulse optical imaging to measure evolution of laser-produced counter-streaming flows

A counter-streaming flow system is a test-bed to investigate the astrophysical collisionless shock（CS） formation in the laboratory. Electrostatic/electromagnetic instabilities, competitively growing in the system and exciting the CS formation, are sensitive to the flows parameters. One of the most important parameters is the velocity, determining what kind of instability contributes to the shock formation. Here we successfully measure the evolution of the counter-streaming flows within one shot using a multi-pulses imaging diagnostic technique. With the technique, the average velocity of the high-density-part（ne ≥ 8–9 × 10^19cm^-3） of the flow is directly measured to be of ～ 10^6cm/s between 7 ns and 17 ns.Meanwhile, the average velocity of the low-density-part（ne ≤ 2 × 10^19cm^-3） can be estimated as ～ 10^7cm/s. The experimental results show that a collisionless shock is formed during the low-density-part of the flow interacting with each other.

Deflections of photoelectron classical trajectories in screened Coulomb potentials of H_2^+

The photoelectron momentum distribution of H＋ in circularly polarized laser fields is studied based on classical trajectory calculations. We screen Coulomb potentials at different radii, and trace trajectories of an ensemble of electrons in such screened Coulomb potentials and circularly polarized laser fields. Simulations show that electron trajectories are bent by Coulomb fields, resulting in the laser-intensity-dependent drift of photoelectron momentum distributions in the laser polarization plane. This study intuitively explains how Coulomb potentials modify photoelectron momenta.

Electron impact excitation of helium atom

A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation(FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method,the convergent e–He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method.

Effects of target pre-heating and expansion on terahertz radiation production from intense laser-solid interactions

The first experimental measurements of intense(～7 × 1019 W cm-2) laser-driven terahertz(THz) radiation from a solid target which is preheated by an intense pulse of laser-accelerated protons is reported. The total energy of the THz radiation is found to decrease by approximately a factor of 2 compared to a cold target reference. This is attributed to an increase in the scale length of the preformed plasma, driven by proton heating, at the front surface of the target,where the THz radiation is generated. The results show the importance of controlling the preplasma scale length for THz production.

Influence of laser contrast on high-order harmonic generation from solid-density plasma surfaces

High-order harmonic generation （HOHG） from the inter- actions of relativistically intense laser pulses with solid-density plasma surfaces has been demonstrated as a promising bright coherent x-ray source in the last de- cade. In contrast with the harmonic generation from la- ser-gas interactions,

Slim OFRS based on a grating input coupler and a microprism sensing surface

A slim optical fingerprint recognition sensor（OFRS） based on a grating input coupler and a microprism sensing surface is proposed.By using a subwavelength grating coupler,input light is coupled into the planar waveguide and the propagation angle is well engineered to avoid image overlap,thus an undistorted fingerprint is captured.For maintaining a thin structure,a microprism array is utilized to facilitate the breaking of total internal reflection under a large diffraction angle from the grating.The feasibility,efficiency,and image quality of the proposed structure are verified and discussed.The device has the advantages of a slim structure,a high image contrast,and a compact architecture,suitable for mobile devices.

Pump phase transfer and its control in hybrid seeded optical parametric amplifiers

Due to the existence of spatial walk-off and/or group-velocity mismatch effects, pump-to-signal phase transfer becomes inevitable during parametric amplification. We experimentally demonstrate that in hybrid seeded optical parametric amplifiers(OPAs) that include two OPA stages seeded by the signal and idler waves, respectively, the phase of the output signal can be restored to its initial value, although there are spatial and temporal phase fluctuations on the pump source. This method significantly relaxes the requirement for high pump beam quality, which is always very stringent in parametric amplification systems. With the introduction of this scheme into birefringent phase-matching OPAs or chirped-pulse OPAs, it should be promising to achieve intense femtosecond laser pulses that are close to the diffraction limit in space and ultra-high contrast in time, simultaneously.

Ultrafast structural dynamics studied by kilohertz time-resolved x-ray diffraction

Ultrashort multi-ke V x-ray pulses are generated by electron plasma produced by the irradiation of femtosecond pulses on metals. These sub-picosecond x-ray pulses have extended the field of x-ray spectroscopy into the femtosecond time domain. However, pulse-to-pulse instability and long data acquisition time restrict the application of ultrashort x-ray systems operating at low repetition rates. Here we report on the performance of a femtosecond laser plasma-induced hard x-ray source that operates at 1-k Hz repetition rate, and provides a flux of 2.0 × 10^10 photons/s of Cu Kαradiation. Using this system for time-resolved x-ray diffraction experiments, we record in real time, the transient processes and structural changes induced by the interaction of 400-nm femtosecond pulse with the surface of a 200-nm thick Au（111） single crystal.