Zhao Yi-Jun

Many-body treatment of the Coulomb hole: application to beryllium

A many-body theoretical treatment of the Coulomb hole is presented. In contrast to the traditional density matrix approach, the interparticle separation distribution function is expressed in terms of the expectation value of the interparticle separation distribution operator. By introducing the second quantisation method, the Goldstone-type linked diagrammatic expansion of the distribution function is obtained, which provides a very clear and convenient frame for the discussion and calculation of the Coulomb hole. The effects of one-body excitation on the Coulomb hole are discussed in detail based on this formulation, and they imply that if the authors define the Coulomb hole with respect to Brueckner instead of Hartree-Fock (HF) orbitals, the Coulomb hole is expected to possess a well behaved form. To calculate the angular parts of the Coulomb hole Goldstone diagrams, the angular momentum graph-an elegant tool-is introduced. By using the formalism and techniques described above, the ground-state Coulomb hole of the beryllium atom is evaluated from a many-body wavefunction, and compared with those derived from CI wavefunctions. The formulation outlined here can be straightforwardly extended to discuss open-shell atoms.

Coherent Beam Combining of Two Fiber Amplifiers Seeded by Multi-Wavelength Fiber Laser

Multi-wavelength seed laser can mitigate stimulated Brillouin scattering (SBS) and improve the output power of the narrow-linewidth fiber amplifier. In this present study, coherent combining of two fiber amplifiers seeded by a multi-wavelength laser is proposed and demonstrated using stochastic parallel gradient descent (SPGD) algorithm. The long-exposure visibility of the far field interference pattern is increased from 0.15 to 0.97 when the system evolves from open-loop to closed-loop. The feasibility of coherent combining of fiber amplifiers seeded by multi-wavelength seed laser is validated.

The 260-W coherent beam combining of two compact fibre amplifier chains

Coherent beam combining of two fibre amplifier chains with a total power of 260 W in a compact system using the stochastic parallel gradient descent (SPGD) algorithm is demonstrated. A 150 MHz linewidth fibre laser is built and introduced for high-power amplification to mitigate stimulated Brillouin scattering (SBS). Compact high-power amplifier chains are built with low power all-fibre system and high-power bulk free-optics fibre amplifiers. When the total power is about 260 W, active phase-locking of two high-power amplifiers is demonstrated using the SPGD algorithm. In closed-loop, the power in the main lobe increases 1.68 times, the visibility is increased from 0 to 0.62, and the phase residual error is less than λ/10.

Coherent beam combining of hybrid phase control in master oscillator-power amplifier configuration

A novel scalable architecture for coherent beam combining with hybrid phase control involving passive phasing and active phasing in master oscillator-power amplifier configuration is presented. Wide-linewidth mutually injected passive phasing fibre laser arrays serve as master oscillators for the power amplifiers, and the active phasing using stochastic parallel gradient descent algorithm is induced. Wide-linewidth seed laser can suppress the stimulated Brillouin scattering effectively and improve the output power of the fibre laser amplifier, while hybrid phase control provides a robust way for in-phase mode coherent beam combining simultaneously. Experiment is performed by active phasing fibre laser amplifiers with passive phasing fibre ring laser array seed lasers. Power encircled in the main-lobe increases 1.57 times and long-exposure fringe contrast is obtained to be 78% when the system evolves from passive phasing to hybrid phasing.

Physical mechanics calculations for the cohesive energies and elastic constants of alkali-halide crystals

The Gordon-Kim method of calculating the interatomic potentials is modified with corrections to the exchange and dispersion interactions, and the interionic potentials in alkali-halide crystals are calculated from Roothaan-Hartree-Fock ionic wavefunctions. The lattice constants, cohesive energies and elastic constants of NaCl, NaF, NaBr, KCl, KF, KBr, RbCl, RbF and RbBr crystals are evaluated using the calculated interionic potentials. The agreement of the results with the experimental data is good.