Search

Essential ingredients for generating a laser are analyzed. Unified understanding on generation mechanisms for both usual lasers (with media composed of atoms, molecules or condensed matter) and free electron lasers are shown. It makes us understand the difficulties in generating a $\gamma$-ray laser. First of all, it is impossible to make a resonator in the $\gamma$-ray region by mirrors, like those made for optic instruments within or near the visible spectrum. The relation between the wavelength $\lambda_r$ of the emitted radiation, and the wiggler period $\lambda_w$ in a free electron laser is $\displaystyle\lambda_r\sim~\lambda_w/\gamma^2$, in which $\gamma$ is the Lorentz factor of the emitting electron.Requiring $\lambda_r$ falls into the $\gamma$-ray region, $\lambda_w$ has to be less than 1 mm.It seems impossible to be realized in a usual free electron laser either. We therefore propose a way to realize it by letting charged particles wiggle in an usual back ground laser. A circularly polarized plane wave laser distorts the electron wave in $x$-$y$ planes,periodically along the $z$ direction, andmodulates the periodicity along the $z$direction. It is the quantum correspondence of the classical wiggling of electrons. Since a laser is a coherentelectromagnetic wave, simple and clean, it is therefore anideal wiggler. To accurately and reliably analyze the whole process, we proposed Quantum Electrodynamics in a Laser. It is equivalent to the Quantum Electrodynamics in Vacuum, and is therefore the most reliable theory nowadays as well. Moreover we noticed that, emitted$\gamma$-photons moving with emitting electrons, itself is a favorable condition to make the stimulated emission easy. Its effect in some sense likethe effect of a resonator. The stimulated emissions amplify the $\gamma$-radiation and make it finally transit into a $\gamma$-ray laser under favorable conditions. In this sense, the generated $\gamma$-ray laser is aQuantum Free Electron Laser. Therefore we clearly concluded that in a head on collision between a suitable mono-energetic electron beam and a monochromatic plane wave laser, a $\gamma$-ray laser should be generated. For an electron beam of density $n_0~=~10^{18}$ m$^{-3}$and energy $E~=~307$ MeV, in the backgroundlaser with $\lambda~=785$ nm and $I~=~10^{19}$ W/m$^2$, theintensity of the output $\gamma$-ray laser is about$5~\times~10^{13}$ W/m$^2$. It is meaningful. Of course, this is a theoretical conclusion under ideal conditions. The competition and the balance between theemission and reabsorption of quanta byelectrons determine the evolution andtherefore the output intensity of the $\gamma$-raylaser. However, Synergetics tells us that there will be a critical point. When the real situation approaches the ideal condition and acrosses over this point, the positive feedback of stimulated emissions leads to a collapse of the created $\gamma$-photon beam into a coherent state. This is a phase transition of the produced $\gamma$-ray into a $\gamma$-ray laser, and is just what we want to search in experiments.

A sharply peaked structure is found in the angular distribution of emitted $\pi^+$ mesons from the photon-proton collisions. It offers a possible way for generating a $\pi^+$-condensation in free space. To make the stimulated emission of $\pi^+$-mesons efficient, a ring resonator is designed., Comment: 4 pages,3 figures

This paper presents a calculation on the obstruction effects for the given large explosion shock wave tube using the ideal nozzle the theory. The relationship among Mach number, Mach number ratio, dynamic pressure ratio in the nozzle throat and blocking area ratio are established according to the fundamental equations of one-dimensional steady flow, which can be taken as the reference of blocking limit design.

By the concept of negativity, we investigate the thermal entanglement in the two-spin ( 1 2 , s ) Heisenberg XXX and XXZ models in the presence of Dzyaloshinskii–Moriya ( D M ) interactions respectively. Through calculation, we know that for the XXZ model, the Δ and s can be used together to control the extent of entanglement and, in particular, to obtain large entanglement. The effect of spin in both models shows that it can increase the critical temperature and the negativity decreases as the spin increases. We found that the DM interaction has different effects on Fermi and Bose systems so it can not only excite entanglement but also affect the entanglement in different spin systems.

We propose a quantization procedure for the nucleon-scalar meson system, in which an arbitrary mean scalar meson field $\phi$ is introduced. The equivalence of this procedure with the usual ones is proven for any given value of $\phi$. By use of this procedure, the scalar meson field in the Walecka's RMFT and in Chin's RHA are quantized around the mean field. Its corrections on these theories are considered by perturbation up to the second order. The arbitrariness of $\phi$ makes us free to fix it at any stage in the calculation. When we fix it in the way of Walecka's RMFT, the quantum corrections are big, and the result does not converge. When we fix it in the way of Chin's RHA, the quantum correction is negligibly small, and the convergence is excellent. It shows that RHA covers the leading part of quantum field theory for nuclear systems and is an excellent zeroth order approximation for further quantum corrections, while the Walecka's RMFT does not. We suggest to fix the parameter $\phi$ at the end of the whole calculation by minimizing the total energy per-nucleon for the nuclear matter or the total energy for the finite nucleus, to make the quantized relativistic mean field theory (QRMFT) a variational method.

We propose a scheme to simultaneously widen and heighten the high-order harmonic plateau on a large scale. More specifically, by adopting a united two-atom system with a suitable inter-nuclear separation instead of a single-atom, the harmonic plateau is widened from Ip + 3.2Up to Ip + 8.5UP; further, by adopting the combined pulse, the extended plateau (harmonics near Ip + 5.6Up) is selectively heightened in excess of 4 orders of magnitude compared with the case of the low-frequency pulse alone. By means of the wavelet transform for the induced dipole of these harmonics, a single x-ray pulse as short as 210 asec is achieved.

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 the conservation and the non-additivity of the information, together with the additivity of the entropy make the entropy increase in an isolated system. The collapse of the entangled quantum state offers an example of the information non-additivity. Nevertheless, the later is also true in other fields, in which the interaction information is important. Examples are classical statistical mechanics, social statistics and financial processes. The second law of thermodynamics is thus proven in its most general form. It is exactly true, not only in quantum and classical physics but also in other processes, in which the information is conservative and non-additive., Comment: 4 pages

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 show that in the quantum transition of an atom interacting with an intense laser of circular frequencyω, the energy difference between the initial and the final states of the atom is not necessarily an integer multiple of thequantum energy ¯hω . This kind of non-integer transition is a true non-perturbation effect in laser-atom interaction.PACS numbers: 03.65.-w, 32.80.Fb, 32.90.+a, 33.60.-qKey words: transitions induced by intense lasers, non-perturbation effect, violation of Bohr condition 1 Introduction It is widely accepted that the Bohr conditionE 2 −E 1 = ±¯hω (1)expresses the energy conservation in the quantum transi-tion from the state with energy E 1 to the state with energyE 2 of the atom, interacting with the electromagnetic fieldof circular frequency ω. It may be generalized toE 2 −E 1 = N¯hω (2)with an integer N, when the atom is interacting with alaser. This generalized Bohr condition is still thought tobe an expression of the energy conservation in the tran-sition, with the number of absorbed or emitted photonsbeing larger than 1. The transitions satisfying Eq. (2)with N>1 have been observed experimentally in formsof the multi-photon ionization (MPI)

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.

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.

A two-body equation of the kaon-proton system with the lowest order relativistic corrections is derived and solved. The scattering lengths and the energy of an unstable bound state are calculated.

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 Kapitza–Dirac effect is investigated in a formalism developed from the formal quantum theory. Numerical calculations yield good agreement with the experimental results.

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.

Applying time-independent non-perturbative formalism to the photo-ionization of hydrogen atom immersed in a strong circularly polarized standing electromagnetic wave, we calculate the shift of energy levels and the distortion of wave functions for the hydrogen atom, the ionization cross section induced by the standing wave, and the angular distribution of photoelectrons and obtain some interesting results.

The electric field in the crystal planar channels is studied by the self-consistent Thomas–Fermi method. The Thomas–Fermi equation and the corresponding boundary conditions are derived for crystal planar channels. The electric field in the channels of silicon crystal, the critical angles and the half-angles for channelling protons in them are calculated numerically. A reasonable agreement with the experimental data is obtained. The results show that the self-consistent Thomas–Fermi method for the crystal channels works well, and microscopic research of the channel electric field with the contributions of all atoms and the atomic polarization being taken into account is practical. We also predict the critical angles of high-energy positron channelling in the same channels for a further check of the theory.

The electric field in the crystal planar channels is studied by the Thomas–Fermi method. The Thomas–Fermi equation and the corresponding boundary conditions are derived for the crystal planar channels. The numerical solution for the electric field in the channels between (110) planes of the single crystal silicon and the critical angles of channelling protons in them are shown. Reasonable agreements with the experimental data are obtained. The results show that the Thomas–Fermi method for the crystal works well in this study, and a microscopic research of the channel electric field with the contribution of all atoms and the atomic ionization being taken into account is practical.

We propose a new version of the relativistic mean field theory for nuclear matter. The theory is based on an effective relativistic Lagrangian, in which, besides interactions via exchange mesons, baryons also interact with each other directly. The direct interaction is introduced to represent the compositeness of the baryon and to simulate the quark-quark interaction between them.

The binding energies per-nucleon for 1654 nuclei, whose mass numbers range from 16 to 263 and charge numbers range from 8 to 106, are calculated by the relativistic mean field theory, with finite nucleon size effect being taken into account. The calculated energy surface goes through the middle of experimental points, and the root mean square deviation for the binding energies per-nucleon is 0.08163 MeV. The numerical results may be well simulated by a droplet model type mass formula. The droplet model is therefore put on the relativistic mean field theoretical foundations.

The possibility of $\gamma-$ray laser generation by the radiation of wiggling electrons in an usual background laser is discussed., Comment: 9 pages,3 figures

We investigate the quantum correlation measured by quantum discord (QD) for thermalized ferromagnetic Heisenberg spin systems in one-dimensional chains and on fractal lattices using the decimation renormalization group approach. It is found that the QD between two non-nearest-neighbor end spins exhibits some interesting behaviors which depend on the anisotropic parameter Δ, the temperature T, and the size of system L. With increasing Δ continuously, the QD possesses a cuspate change at Δ = 0 which is a critical point of quantum phase transition (QPT). There presents the “regrowth” tendency of QD with increasing T at Δ 0. As the size of the system L becomes large, there still exists considerable thermal QD between long-distance end sites in spin chains and on the fractal lattices even at unentangled states, and the long-distance QD can spotlight the presence of QPT. The robustness of QD on the diamond-type hierarchical lattices is stronger than that in spin chains and Koch curves, which indicates that the fractal can affect the behaviors of quantum correlation.

We calculate nonperturbatively the irfluence of a strong circularly polarized laser beam on the hydrogen atom energy levels by making use of the time-independent formalism proposed by one of us. The photoionization cross section of the hydrogen atom irradiated by this laser beam and the angular distribution of photoelectrons are also calculated. From the numerical results we clearly see the intensity dependence of the whole photoionization process,including the intensity dependence of the photoelectron energies.

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.

We find: (i) The Lee–Wick type relativistic mean-field theory with finite nucleon size effect can reproduce the binding energies for all nuclei over the nuclide table quite well. For 1654 nuclei, whose mass numbers range from 16 to 263 and charge numbers range from 8 to 106, the calculated binding energies are near to the corresponding experimental values with a systematical deviation of about 5.74%. (ii) The lowering of the calculated nuclear masses, by including Coulomb energy into the variational calculations, is very small.

We examine the role of relativistic finite baryon volume effect in the phase transition between hadronic matter and quark-gluon plasma at vanishing baryon density. It is found that the appearance of abnormal state at high temperature may enhance the baryon-antibaryon excitation, which has large influence on the quark-gluon plasma formation. The numerical results show that the occurence of this phase transition depends on how to extrapolate the nucleon-scalar meson coupling constant to the baryonic resonance-scalar meson coupling.

We reduce the many-body problem to a multi-channel few-body problem by the AGS method. The channels may be chosen according to the problem under consideration and the reduction is formally exact. For the nuclear reaction we may choose some one-body channels to represent compound nucleus and choose some two- or more-body channels to represent open reaction channels. We then apply formal collision theory to this multi-channel system. Direct reaction, resonant reaction and their interference emerge. There are also distortions of ingoing and outgoing waves in compound nucleus formation and decay respectively. The omission of all but one open channel leads to the optical model, and an incomplete consideration of the open channels may lead to a multi-channel generalization of the optical model. Nonnucleon degrees of freedom as well as relativity may be included in principle. The reaction induced by particles other than nuclei may be considered on the same footing.

The importance of the quantum recoil in the possible gamma-ray amplification by stimulated emission of radiation from positrons channelling in an acoustically excited crystal is emphasized.

We extend our work on the finite value of mean π-field in the relativistic mean field theory to the derivative coupling models for nuclear matter proposed by Zimanyi and Moszkowski. We show that a finite mean π-field may lower the energy per nucleon at a not too high density for all of those models. This qualitative result seems true in general and is model independent, although the quantitative details may be different for different models.

We show that the collapse of the entangled quantum state makes the entropy increase in an isolated system. The second law of thermodynamics is thus proven in its most general form.

We compare a relativistic and thermodynamically consistent treatment for the finite-volume effect of baryons in the phase transition between hadronic matter and quark-gluon plasma, with the previous non-relativistic treatment. We find that, according to the relativistic theory, this phase transition is possible only when the baryonic spectrum is upper bounded.

The meson-nucleon correlation truncation approximation is presented for an application to nuclear matter, and the effects of the meson-nucleon correlation on the nucleon mass and saturation energy, as well as the pressure of nuclear matter, are calculated. Our results are compared with those of the mean-field approximation, and show that the effects of the meson-nucleon correlations are important.

The intensity dependence of the energy and the angular distribution for photoelectrons ejected by a circularly polarized laser beam is derived. The energy shift is similar to that of a combined Zeeman–Stark effect in magnetic and electric fields perpendicular to each other.

In an approximately chiral symmetric nuclear model consistent with the empirical nuclear data, we find that the medium pion mass approaches zero when the nuclear density approaches a critical value. At this critical density a chiral rotation occurs. The binding energy pernucleon jumps from about 16 MeV to 85 MeV. Since the chiral angle is not zero, we call this new state the pi-abnormal nuclear state. In this new state the pion mass becomes about 140 MeV again. Then it decreases with further increase of the nuclear density until it reaches another critical point. At this second point, the chiral angle reaches π. The pion mass starts rising. We identify this phase with the Lee–Wick's abnormal nuclear state.

Quantum electrodynamics in a laser is formulated, in which the electron-laser interaction is exactly considered, while the interaction of an electron and a single photon is considered by perturbation. The formulation is applied to the electron-laser collisions. The effect of coherence between photons in the laser is therefore fully considered in these collisions. The possibility of $\gamma-$ray laser generation by use of this kind of collision is discussed., Comment: 15 pages, 2 figures

With the help of a model calculation, the following features in the multiphoton detachment rate spectrum of negative ions are shown: (1) the global behavior of the rate, as a function of the photon frequency, does follow the so-called `step-like' pattern; (2) a Wigner-type cusp occurs at every threshold open for the lower photon number channel; (3) a clear dip appears at a certain frequency point slightly lower than each threshold frequency. All these features are interpreted as the general characteristics of multiphoton detachments on the R-matrix–Floquet analysis. Comparisons are made with the previous results. To the best of our knowledge, the third feature may be for the first time explained in this paper, though it is not first found by us.

We show: (1) The photoelectric effect induced by a circularly polarized light beam is exactly equivalent to a quantum transition induced by a time independent perturbation between stationary states. The equivalent energy level of the target system is then light intensity dependent. (2) This energy shift, in the dipole approximation, is similar to that of a combined Zeeman-Stark effect in magnetic and electric fields perpendicular to each other.

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.

Collision cross sections are calculated using the R-matrix method for excitations between the three lowest LS states for Na-like Cu ion. The complex resonance structures are investigated. The collision rate coefficients have been calculated assuming a Maxwellian distribution of electron-impact energies. The results of the collision cross sections are in good agreement with those of the other theory.

We generalize the Walecka model for nuclear matter by including the π-field. It is found that a finite mean π-field may lower the energy per nucleon even in the nuclear matter of subnormal density. A mean π-field may significantly change the nuclear equation of state. The importance of considering the π-field in the relativistic mean field theory for nuclear matter is therefore emphasized.

A previous thermodynamically consistent procedure for considering the finite volume effect of nucleons in nuclear matter is developed to be relativistic. Parameters are determined by fitting all five empirical data for normal nuclear matter. The resulting nuclear equations of state may be used in researches for neutron stars and for phase transitions between nuclear matter and quark-gluon plasma.

We revise our previous calculation of the finite baryon size effect on the mass limit for neutron stars by making the formulation be relativistic. The result is still consistent with the observational data.

A previous thermodynamically consistent procedure for considering the finite volume effect of nucleons in nuclear matter is developed to be relativistic. Parameters are determined by fitting all five empirical data for normal nuclear matter. The resulting nuclear equations of state may be used in researches for neutron stars and for phase transitions between nuclear matter and quarkgluon plasma.

By relativity we show that, although the superluminal motion of classical particles is forbidden, the superluminal transportation of quanta of any massive matter field is possible. Exact theoretical derivation and precise numerical computation are presented. To search the superluminal phenomena is therefore still meaningful., Comment: 7 pages, 2 figures This paper has been withdrawn by the author, because a subsequent analytical derivation shows the wave function (5) is exactly zero in the superluminal region. Its value of order of 10^{-6} shown in fig.2 is therefore from the accumulative error of numerous computation and cancellation in the numerical calculation, which is out of the control in the program

The rapid thermal annealing temperature dependence of the recrystallization, Yb migration and its optical activation were studied for Yb-implanted silicon. For the annealing regime 800-1000-degrees-C, the Yb segregates both at the crystal/amorphous interface and at the surface, which is different from the usual segregation of Er at the crystal/amorphous interface, and the efficiency of optical activation also increases with annealing temperature. However, the amorphous layer regrows completely and no photoluminescence is observed after the annealing at 1200-degrees-C.

We study a thermodynamically consistent implementation of the nucleon volume in the mean field theory, and find that this volume has large consequences on the properties of hadronic matter under extreme conditions such as in astrophysical objects and high energy heavy-ion collisions. It is shown that we can reproduce the critical temperature $T_{c}\simeq 200$ MeV predicted by lattice QCD calculations for the phase transition from hadronic matter to quark-gluon plasma, by using parameters which are adjusted to fit all empirical data for normal nuclear matter., Comment: 11 Latex pages, 4 figures upon request

We developed the MIT bag crystal model for nuclear matter in two aspects. First, we proved a {Delta}{mu}=4 selection rule in the harmonic expansion of quark wave function by group theory. It enables us to push the maximum Dirac quantum number {kappa}{sub {ital m}} up from 7 to 15, therefore improving our calculation for the energy band and wave functions of quarks. Then, by a multipole expansion of the color fields we calculate the color interaction energy between quarks. These developments enable us to calculate the energy per nucleon in nuclear matter as done previously for a free nucleon. A nuclear equation of state is derived.