International Journal of Modern Physics B

Lasers emit light with a very high degree of monochromaticity, directionality and intensity. They can produce much higher intensities than incoherent light sources, such as incandescent lamps, fluorescent tubes and arcs. The first operating laser was realized in 1960, and much early research was funded by military agencies, but at the present time the commercial laser market is four times as large as the military market. Most applications of lasers are for peaceful purposes. Among the most important of these are fiber-optic communications and laser surgery. Other applications include laser printing, laser machining, construction alignment, and data storage on CD disks. Some military uses of lasers are also reviewed.

In a many-body perturbation treatment of electronic excitations, one has to solve the so-called Bethe–Salpeter equation (BSE) for the kernel (vertex) describing the interaction between electrons. In general, the BSE exhibits a non-local and frequency-dependent screened interaction and consequently it is extremely difficult to solve. We have developed a scheme that solves the BSE equation iteratively, including dynamically screening, by considering the change in the electron self-energy upon applying a time-dependent field. The BSE is obtained from the self-energy in the GW approximation (GWA) using the Schwinger functional technique. We apply our formalism to a simple model system and discuss briefly changes in the charge response, when dynamical screening is taken into account.

In the ferromagnetic phase of the 3D electron system, it is assumed that the spins of all the electrons are arranged in a parallel manner. The ferromagnetically ordered electrons are represented by the structure dependent Wannier functions. The ground state energies of the ferromagnetically ordered electron crystals corresponding to sc, bcc, fcc, diamond and perovskite structures are computed with Gaussian type and Yukawa type positive backgrounds. The stability of these structures is analyzed. In each case, the possibility of the Wigner electrons having cubic or spherical constant energy surface (the region of integration in momentum space) is considered for the range of r_s values corresponding to low densities. The effect of correlation energy is suitably taken into account. The range of low density region favorable for Wigner crystallization is found to be at 6.0×10¹⁹/cm³. It is found that the ferromagnetically ordered electrons crystallize into fcc lattice in the low density limit with Yukawa type positive background.

Coulomb repulsion between two moving electrons loses its spherical symmetry due to relativistic effects. In presence of a uniform positive ion background, this asymmetry uncovers an angular dependent attraction potential in the direction of motion. The quantum mechanical response to such an attraction potential is obtained through perturbation. It is shown that the transition amplitude between states with the symmetry of the attraction potential becomes negative and if the density of states is anisotropic, occurrence of a superconducting state becomes possible.

We have studied paramagnetic Mn²⁺ ions present in the shells of today's univalve freshwater snails, Sinotaia ingallsiana (FS), Pila ampullaceal (PA), Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus which are abundant in Thailand. The FS, PA and AG shells in our study were ground into fine powder. A set of seven samples was each then separately annealed for 2 hours in air atmosphere at 300°C, 400°C, 450°C, 500°C, 550°C, 600°C and 900°C, respectively, while the FFS powder was characterized as received. The FS, PA and PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments higher than 450°C of the FS, PA and PCL powder samples resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of high temperature annealed FS, PA and PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but not yet completed, although they remained under the pressure and temperature of the Earth's crust over millions of years. Our detailed ESR spectral analyses of FS, PA, PCL and FFS show that Mn²⁺ ions enter Ca²⁺ sites during a biomineralization process. Typical simulated ESR parameters of FS-500 of Mn²⁺ at a uniaxial site of calcite are g_x=g_y=2.078±0.001, g_z=2.002±0.001, A_x=A_y=87.50±1.00 G, A_z=89.00±1.00 G and D=115±1 G, respectively. It is surprising to find that the ratio of Mn²⁺ concentration present in FFS to those in FS, PA and PCL shells evaluated from ESR spectra is as much as 10:1. It is thus possible to gain some insight of manganese incorporation into the freshwater shells during the biomineralization process.

We realized SU(1,1) Lie algebra in terms of the appropriate SU(1,1) generators for the time-dependent quadratic Hamiltonian system perturbed by a singularity. Exact quantum states of the system are investigated using SU(1,1) Lie algebra. Various expectation values in two kinds of the generalized SU(1,1) coherent states, that is, BG coherent states and Perelomov coherent states are derived. We applied our study to the CKOPS (Caldirola–Kanai oscillator perturbed by a singularity). Due to the damping constant γ, the probability density of the SU(1,1) coherent states for the CKOPS converged to the center with time. The time evolution of the probability density in SU(1,1) coherent states for the CKOPS are very similar to the classical trajectory.

The self-energy is received using the theory group and field techniques, based on the wave functions of the classes of point symmetry group and accounting for the two-particle system. It contains components responsible not only for relaxation processes but also for the oscillating ones, caused by a different degree of occupation of the class of point symmetry group by particles of the structure. Analyzing the character of energy oscillations depending on the degree of the class occupation, the mechanisms of diffusion, catalysis, chemical reactions and Le-Shatelje principle are described.

The structure and transport properties of perovskite (La_1-xY_x)_2/3Ca_1/3MnO₃ (0≤x≤0.3) systems are systematically investigated. It is found that all the specimens show a single-phase structure and reveal a direct relationship between the Curie temperature T_c and the average ionic radius <r_A> of La site. With increasing Y³⁺ doped content, the metal-insulator transition temperature T_MI (M-I) shifts to lower temperature. While the relevant resistivity peak ρ_p is sharp increased, for the specimens with large doping content, x=0.3, it has enhanced eight orders of magnitudes larger than the non-doped samples (x=0.0). At high concentration area, that is to say, when x>0.1, magnetic studies show a gradual increase of antiferromagnetic interaction with an increase of x, ultimately leading to a spatial-spin disorders, that is, spin-glass-like state for x=0.2 and x=0.3 compounds at about 35 K. The results show that it has connected a reduction of T_c and an increase in magnetoresistance with a decrease in the microstructural Mn-O-Mn bond angle.