It is possible for core leaky mode to couple with cladding defect leaky mode when the cladding defect is close to fiber core. Dispersion properties and propagation loss of core mode will be affected in some extent once the coupling occurs. But a complete coupling between two leaky modes not always happens even the phase matching condition is satisfied. Leaky mode coupling in photonic crystal fiber with a hybrid cladding which includes low-index and high-index inclusions at the same time is numerically investigated based on a full vector finite element method. It is found that not only phase matching but also loss matching plays an important role in leaky mode coupling. The originally intersecting dispersion curves for the two leaky modes will split and become another two new curves due to the anti-crossing effect when both the real and imaginary parts of their mode effective refractive indices are equal. There is not splitting but some perturbation in dispersion curves for the two phase matching leaky modes when their losses are not equal. A theoretic explanation is also given to these phenomena.

A theory of Bragg scattering of atoms is presented in which atoms are scattered by counterpropagating optical fields having different frequencies. It is shown that, for this geometry, the system reduces to that encountered in the pump-probe spectroscopy of two or multilevel systems. As a result, one can tune the Bragg resonances by varying the frequency difference between the optical fields. The possiblity of using these techniques to construct an atom-beam splitter, whose output arms are separated in momentum space by a hundred photon momenta, is discussed.

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A Monte Carlo model was established to simulate polarized scattering fields of two-dimensional rough surfaces based on the Kirchhoff approximation. Based on this model, numerical studies of the hemispherical distribution of Stokes vectors of scattered light from dielectric and metal rough surfaces were carried out. These surfaces have Gaussian distributions with correlation length of 3.1 mm and standard deviation varying between 0.1 and 0.6 mm. The results reveal that the V component of metal surfaces has peaks antisymmetric with the incident plane, whereas the V component of dielectric surfaces is almost zero. We consider that this property of the V component would provide a new method which could be used to distinguish the target material.