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Using a variational method, we derive the optimal population distribution of angular momentum eigenstates for any given population range in a rotational wavepacket within the field-free cyclic state orientation framework. Correspondingly, we devise a train of half-cycle pulse clusters to purposively make the structure of the computed wavepacket approach the optimal population distribution, so that we can now utilize much more powerful means to realize an ideal orientation goal.

We show that two trains of half-cycle pulses (HCPs) with different amplitudes irradiating alternately on polar molecules can achieve a remarkable enhancement of field-free orientation compared with the case of an equal amplitude HCPs train for the same pulse separation. This kind of orientation enhancements is mainly due to an optimal adjustment of the population distribution on every field-free angular momentum eigenstate, in which the populations on the undesired states of high angular momenta are effectively suppressed, and the populations on the desired states of low angular momenta are correspondingly promoted.

We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.

Electronic structures of PbMoO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Direc–Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centres have donor energy levels in the forbidden band. The optical transition energies are 2.166 eV and 2.197 eV, respectively, corresponding to the 580 nm absorption bands in PbMoO4 crystal. The 580 nm absorption band in PbMoO4 is originated from the F-type colour centres.

The possible defect models of Y3+:PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y3+ ions are studied by using the general utility lattice program (GULP). The calculated results indicate that in the lightly doped Y3+:PWO crystal, the main compensating mechanism is [2YPb++VPb2−], and in the heavily doped Y3+:PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb+, forming defect clusters of [2YPb++Oi2−] in the crystal. The electronic structures of Y3+:PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420 nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.

Recently, two papers presented by Ortigoso et al. [Phys. Rev. Lett. 93 (2004) 073001 and Phys. Rev. A 72 (2005) 053401] develop a novel strategy in which the best sustainable molecular alignment/orientation has been achieved. We intend to analyse the dynamic mechanisms, including those Ortigoso et al. have not clarified.

Electronic structures of PbWO4 crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac–Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F+ centres have donor energy levels in the forbidden bands. Their optical transition energies are 1.84 eV and 2.21 eV, respectively, which correspond to the 680 nm and 550 nm absorption bands. It is predicted that the 680 nm and 550 nm absorption bands originate from the F and F+ centres in PbWO4 crystals.

We present a high-order harmonic generation (HHG) spectrum from a united two-atom system exposed to a combined laser pulse, by numerically solving a one-dimensional time-dependent Schrodinger equation. The combined laser pulse is composed of a low-frequency femtosecond pulse and a high-frequency attosecond one with respective appropriate amplitudes. For a suitable inter-nuclear separation, the harmonic emission efficiencies near the second cutoff of the extended plateau can be effectively enhanced by more than four orders of magnitude compared with the case of the low-frequency pulse alone. Such a combined pulse irradiating on the united two-atom system ionizes each atom, in a large rate (but not to a too large ionization yield), mainly at a particular time-interval. When the ionized electron from an atom reaches at the vicinity of the other atom and recombines with it, significant HHG enhancement is achieved for particular harmonics. This result, to our knowledge, is one of the best up to now in the endeavor for dramatically extending the width and simultaneously enhancing the height of the plateau.

We present the high-order harmonic generation spectrum from a united two-atom system simultaneously exposed to a fundamental Ti:sapphire and its 33rd harmonic (H33) lasers by numerically solving a one-dimensional time-dependent Schrodinger equation. At a suitable inter-nuclear separation, the harmonic plateau is widened from Ip+3.2Up in the single-atom case up to Ip+5.6Up in the united-atom case. Furthermore, the plateau is heightened in excess of six orders of magnitude by using the combined lasers compared with the case of the fundamental laser alone. Such a scheme can step by step accomplish the following processes: through a single H33 photon resonance transition an appropriate amount of electrons are first populated to an excited state, in which the electrons are easily ionized and subsequently accelerated by the fundamental laser; then they can recombine with the neighbouring atom, so that high-efficiency emissions of the harmonics beyond Ip+3.2Up are successfully realized.

We present a scheme aiming at the field-free orientation of molecules with smaller permanent dipole moments under the framework of the half-cycle pulse (HCP) method. Taking the HCCCl molecule as an example, we show that a train of identical HCPs with special time intervals can considerably raise the level of the orientation. The scheme is analytically interpreted in terms of intermittent Rabi oscillations by referring to a simplified two-state model.

The electronic structures, dielectric functions, complex refractive indices and absorption spectra for a perfect PbWO4 (PWO) crystal and the PWO crystals containing lead vacancy VPb2− have been calculated using a full-potential (linearized) augmented plane-wave (LAPW) + local orbitals (LO) method with the lattice structure optimized. The peaks of the absorption spectra corresponding to the electronic transitions have been studied. The calculated results indicate that the absorption band of the perfect PWO crystal does not occur in the visible region. However, the PWO crystal containing VPb2− has two additional absorption bands in this region. The two bands can be well decomposed into four gaussian-shape bands peaking at 350 nm, 405 nm, 550 nm and 670 nm, respectively, which coincide well with the 350 nm, 420 nm, 550 nm and 680 nm absorption bands measured in PWO crystals. Therefore, it can be concluded that the 350 nm, 420 nm, 550 nm and 680 nm absorption bands are related to the existence of VPb2− in the PWO crystal.

The electronic structures for three types of PbWO4 (PWO) crystals, the perfect PWO, the PWO containing lead vacancy (PWO-VPb) and fluorine doped PWO crystal (F−:PWO), are systematically studied within the framework of density functional theory. The computational results show that the Pb 6s state situates below the valence band so that Pb2+ ions are unable to trap holes forming Pb3+ or Pb4+ to compensate for VPb2−. The hole-trappers in PWO-VPb are O2− ions. Two of the longer-bond O2− ions share a hole forming O23−, and four of the longer-bond oxygen ions trap two holes forming an associated color centre [O23−-VPb-O23−], which may be the origin of the 420 nm absorption band. It is also concluded that the doping of F− would reduce the band gap and F− ions substituting for O2− can effectively restrict the formation of [O23−-VPb-O23−] and weaken the 420 nm absorption band and hence enhance the scintillation property of PWO.

The lattice structures around one lead vacancy VPb2− in PbWO4 are studied within the framework of the full-relativistic density functional theory. Using the conjugate gradient method, we optimize the geometry of the ions around VPb2− by moving the ions within the sub-cell until specified tolerance is satisfied. We obtain the geometric positions of ions around VPb2− after optimization. The calculated results indicate that there would be local lattice distortion caused by the existence of VPb2−. The electronic structures of both the optimized and pre-optimized PWO containing VPb2− have been calculated. The density of states of the distorted PWO indicates that the energy gap between the 2p state of O2− and the 5d state of W6+ is 3.90 eV, which shows that the distorted W–O tetrahedron may be the 420 nm luminescence centre.

We present high-order harmonic generation spectra resulted from a single-electron model molecular ion exposed to intense laser fields by numerically solving a one-dimensional time-dependent Schr?dinger equation. There are three plateaus in the spectra and the maximal cutoff energy is Ip+8.5Up, when the inter-nuclear distance R equals ??0/2. Here Ip is the ionization potential and Up = E02/(4?2) is the ponderomotive potential with E0 and ? being the laser electric field amplitude and the central frequency. The harmonic structures are well interpreted by a modified three-step model in which the effects of the electron reflected by the non-parent ion are stressed.

Using the Hamiltonian lattice gauge theory, we perform some variational calculations to obtain the ground-state energy of SU(3) gauge field and scalar (0+ + ) glueball mass. The agreement of our data with the strong and weak expansion results in the corresponding limits indicates that this method can provide us with reliable information in the most interesting medium region. The trial wavefunction used in our variational method is also proven to be a good first approximation of the ground-state of the SU(3) gauge field. Upgrading this function according to correlations of adjacent plaquettes may mean better results.

Amorphous carbon films are deposited on the Mo film/ceramic substrates, which are pretreated by a laser spattering chiselling technique (2 line/mm), by using the microwave chemical vapour deposition technique. The films are characterized by x-ray diffraction, Raman spectrum, optical microscopy, and scanning electron microscopy. The experimental result indicates that the laser spattering chiselling pretreated techniques can essentially improve the field emission uniformity and the emission site density of the amorphous carbon thin film devices so that its emission site density can reach the level of actual application (undistinguishable by naked eye) from a broad well-proportioned emission area of 50 mm × 50 mm. This kind of device can show various digits and words clearly. The lowest turn-on field below 1 V/m, the emission current density over 5.0±0.1 mA/cm2, and the highest luminance 1.0×103 cd/m2 are obtained. Meanwhile, the role of the laser spattering chiselling techniques in improving the field emission properties of the amorphous carbon film are explained.

An x-ray laser shadowgraphy experiment was conducted on Xingguang-II laser facility in 1996. A multi-layer spherical mirror was used as an imaging element and a high sensitivity CCD camera as a detector. We measured the near-field image of the Ti x-ray laser beam. With a Ti x-ray laser beam as a backlight source, we obtained a clear Cu mesh image, demonstrating the potential as advanced diagnostic measurements to study high density plasmas in inertial confinement fusion research.

With the help of a model calculation based on the R-matrix - Floquet theory, the variability of multiphoton detachment rate versus laser intensity is in detail investigated. A number of interesting regularities, which can not be understood in the lowest order perturbation theory, is found out and interpreted.

The influence of the relativistic finite volume effect of nucleons on the properties of dense nuclear matter is examined at finite temperature and it is found that the abnormal nuclear state can appear at sufficiently high density. Then, by using this methed the phase transition between hadronic matter and quark-gluon plasma is studied. The numerical results show that the value of nucleon radius is important for reproducing this phase transition correctly.

Using a linearly polarized, phase-stabilized 3-fs driving pulse of 800 nm central wavelength shape-optimized on its ascending edge by its an amplitude-reduced pulse irradiating on a superposition state of the helium atom, we demonstrate theoretically the generation of a super strong isolated 176-attosecond pulse in the spectral region of 93–124 eV. The unusually high intensity of this attosecond pulse is marked by the Rabi-like oscillations emerging in the time-dependent populations of the ground state and the continuum during the occurrence of the electron recombination, which is for the first time observed in this work.

Using a linearly polarized, phase-stabilized 2.66-femtosecond driving pulse of 400 nm central wavelength orthogonally combined with another linearly polarized long pulse of 800 nm central wavelength irradiating jointly on the helium atom, we demonstrate theoretically the generation of a clean isolated 80-attosecond pulse in the spectral region of 93–155 electron volts in a two-dimensional model.