MODELING EVOLUTION OF INTERNAL WAVES IN SOUTH CHINA SEA

Internal waves are an important factor in the design of drill operations and production in deep water, because the waves have very large amplitude and may induce large horizontal velocity. How the internal waves occur and propagate over benthal terrain is of great concern for ocean engineers. In the present paper, we have formulated a mathematical model of internal wave propagation in a two-layer deep water, which involves the effects of friction, dissipation and shoaling, and is capable of manifesting the variation of the amplitude and the velocity pattern. After calibration by field data measured at the Continental Slope in the Northern South China Sea, we have applied the model to the South China Sea, investigating the westward propagation of internal waves from the Luzon Strait, where internal waves originate due to the interaction of benthal ridge and tides. We find that the internal wave induced velocity profile is obviously characterized by the opposite flow below and above the pycnocline, which results in a strong shear, threatening safety of ocean structures, such as mooring system of oil platform, risers, etc. When internal waves propagate westwards, the amplitude attenuates due to the effects of friction and dissipation. The preliminary results show that the amplitude is likely to become half of its initial value at Luzon Strait when the internal waves propagate about 400 kilometers westwards.

Space-frequency coupling, conical waves, and small-scale filamentation in water

Numerical simulations of fs laser propagation in water have been made to explain the small-scale filaments in water we have observed by a nonlinear fluorescence technique. Some analytical descriptions combined with numerical simulations show that a space-frequency coupling mainly from the interplay among self-phase modulation, dispersion and phase mismatching will reshape the laser beam into a conical wave which plays a major role of energy redistribution and can prevent laser beam from self-guiding over a long distance. An effective group velocity dispersion is introduced to explain the pulse broadening and compression in the filamentation. (c) 2005 American Institute of Physics.

Formation of X-waves at fundamental and harmonics by infrared femtosecond pulse filamentation in air

We experimentally observe the formation of X-waves at fundamental, third harmonic, and fifth harmonic wavelengths by infrared (central wavelength at similar to 1500 nm) femtosecond laser pulse filamentation in air. By fitting the angularly resolved spectra of the fundamental and harmonic waves using X-wave relations, we confirm that all the X-waves have nearly the same group velocity, indicating that they are locked in space and time during their propagation in filament.

Interaction of oblique incident electromagnetic wave with relativistic ionization front

Interactions of oblique incident probe wave with oncoming ionization fronts have been investigated using moving boundary conditions. Field conversion coefficients of reflection, transmission and magnetic modes produced in the interactions are derived. Phase matching conditions at the front and frequency up-shifting formulas for the three modes are also presented.

Quantum superchemistry in an output coupler of coherent matter waves

We investigate the quantum superchemistry or Bose-enhanced atom-molecule conversions in a coherent output coupler of matter waves, as a simple generalization of the two-color photoassociation. The stimulated effects of molecular output step and atomic revivals are exhibited by steering the rf output couplings. The quantum noise-induced molecular damping occurs near a total conversion in a levitation trap. This suggests a feasible two-trap scheme to make a stable coherent molecular beam.

Wavefront conversion by local volume holograms between cylindrical and plane waves with reconstruction at a different readout wavelength

Based on the two-dimensional coupled-wave theory, the wavefront conversion between cylindrical and plane waves by local volume holograms recorded at 632.8 nm and reconstructed at 800 nm is investigated. The proposed model can realize the 90 degrees holographic readout at a different readout wavelength. The analytical integral solutions for the amplitudes of the space harmonics of the field inside the transmission geometry are presented. The values of the off-Bragg parameter at the reconstructed process and the diffracted beam's amplitude distribution are analysed. In addition, the dependences of diffraction efficiency on the focal length of the recording cylindrical wave and on the geometrical dimensions of the grating are discussed. Furthermore, the focusing properties of this photorefractive holographic cylindrical lens are analysed.

Anisotropic-source-induced changes of the degree of polarization of stochastic electromagnetic beams on propagation

It is shown that stochastic electromagnetic beams may have different degrees of polarization on propagation, even though they have the same coherence properties in the source plane. This fact is due to a possible difference in the anisotropy of the field in the source plane. The result is illustrated by some examples.

Change in degree of coherence of partially coherent electromagnetic beams propagating through atmospheric turbulence

We study the change in the degree of coherence of partially coherent electromagnetic beam (so called electromagnetic Gaussian Schell-model beam). It is shown analytically that with a fixed set of source parameters and under a particular atmospheric turbulence model, an electromagnetic Gaussian Schell-model beam propagating through atmospheric turbulence reaches its maximum value of coherence after the beam propagates a particular distance, and the effective width of the spectral degree of coherence also has its maximum value. This phenomenon is independent of the used turbulence model. The results are illustrated by numerical curves. (c) 2006 Elsevier B.V. All rights reserved.

Changes in the coherence of quasi-monochromatic electromagnetic Gaussian Schell-model beams propagating through turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the mutual coherence function of quasi-monochromatic electromagnetic Gaussian Schell-model (EGSM) beams propagating through turbulent atmosphere is derived analytically. By employing the lateral and the longitudinal coherence length of EGSM beams to characterize the spatial and the temporal coherence of the beams, the behavior of changes in the spatial and the temporal coherence of those beams is studied. The results show that with a fixed set of beam parameters and under particular atmospheric turbulence model, the lateral coherence of an EGSM beam reaches its maximum value as the beam propagates a certain distance in the turbulent atmosphere, then it begins degrading and keeps decreasing along with the further distance. However, the longitudinal coherence length of an EGSM beam keeps unchanging in this propagation. Lastly, a qualitative explanation is given to these results. (c) 2007 Elsevier B.V. All rights reserved.

Effects of coherence on anisotropic electromagnetic Gaussian-Schell model beams on propagation

An analytical formula for the cross-spectral density matrix of the electric field of anisotropic electromagnetic Gaussian-Schell model beams propagating in free space is derived by using a tensor method. The effects of coherence on those beams are studied. It is shown that two anisotropic stochastic electromagnetic beams that propagate from the source plane z = 0 into the half-space z > 0 may have different beam shapes (i.e., spectral density) and states of polarization in the half-space, even though they have the same beam shape and states of polarization in the source plane. This fact is due to a difference in the coherence properties of the field in the source plane. (C) 2007 Optical Society of America.

New doubly periodic waves of the (2+1)-dimensional double sine-Gordon equation

New exact solutions of the (2 + 1)-dimensional double sine-Gordon equation are studied by introducing the modified mapping relations between the cubic nonlinear Klein-Gordon system and double sine-Gordon equation. Two arbitrary functions are included into the Jacobi elliptic function solutions. New doubly periodic wave solutions are obtained and displayed graphically by proper selections of the arbitrary functions.

Electromagnetic fields and transmission properties in tapered hollow metallic waveguides

We analyze the electromagnetic spatital distributions and address an important issue of the transmission properties of spherical transverse-electric (TE) and transverse-magnetic (TM) eigenmodes within a tapered hollow metallic waveguide in detail. Explicit analytical expressions for the spatital distributions of electromagnetic field components, attenuation constant, phase constant and wave impedance are derived. Accurate eigenvalues obtained numerically are used to study the dependences of the transmission properties on the taper angle, the mode as well as the length of the waveguide. It is shown that all modes run continuously from a propagating through a transition to an evanescent region and the value of the attenuation increases as the distance from the cone vertex and the cone angle decrease. A strict distinction between pure propagating and pure evanescent modes cannot be achieved. One mode after the other reaches cutoff in the tapered hollow metallic waveguide as the distance from the cone vertex desreases. (C) 2008 Optical Society of America