Biomedical subjects

Xue-Hua Wang

Publications and source records attributed to Xue-Hua Wang.

7 recordsLinked to original sources

PubMed2006

Switching control of spontaneous emission by polarized atoms in two-dimensional photonic crystals.

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.

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PubMed2005

Green's function for photonic crystal slabs.

Green's tensors for photonic crystal (PC) slabs are numerically solved by the coupled-dipole approximation (CDA) technique. The obtained components of Green's tensors satisfy discontinuous or continuous conditions at interfaces of scatterers. This shows that the CDA technique is very applicable to studying the properties of PC slabs. Green's tensors exhibit obviously periodic oscillation with the increase of the number of scatterers; furthermore, the effect of each scatterer on Green's tensors displays a localization feature in the sample containing one row of scatterers; on the contrary, this localized effect disappears in the sample consisting of multiple rows of scatterers.

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PubMed2005

Photonic band gap effects on spontaneous emission lifetimes of an assembly of atoms in two-dimensional photonic crystals.

The lifetime distribution functions of the spontaneous emission (SE) of the excited atoms embedded in two-dimensional (2D) photonic crystals (PCs) with square lattice, consisting of square air rods in dielectric medium with different filling factors, are calculated by using the plane wave expansion method. The numerical results show that the SE in the 2D PCs cannot be prohibited completely but it can be inhibited intensively by the pseudo-PBG of the PCs. In the pseudoband edges, the SE is accelerated obviously. The reduced average lifetime of the excited atoms and the extension of the reduced lifetime distribution in the 2D PCs both are the same as those in the 3D PCs in the order of magnitude. Our results provide an available way to control the behavior of the SE by changing the structures of the 2D PCs.

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PubMed2004

Unified treatment of fluorescence and raman scattering processes near metal surfaces.

We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.

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PubMed2004

Giant lamb shift in photonic crystals.

We obtain a general result for the Lamb shift of excited states of multilevel atoms in inhomogeneous electromagnetic structures and apply it to study atomic hydrogen in inverse-opal photonic crystals. We find that the photonic-crystal environment can lead to very large values of the Lamb shift, as compared to the case of vacuum. We also suggest that the position-dependent Lamb shift should extend from a single level to a miniband for an assembly of atoms with random distribution in space, similar to the velocity-dependent Doppler effect in atomic/molecular gases.

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PubMed2003

Decay kinetic properties of atoms in photonic crystals with absolute gaps.

Decay kinetic properties of a two-level atom near the band edges of photonic crystals (PCs) with absolute gaps are studied based on the Green's function expression for the evolution operator. The local coupling strength between the photons and an atom is evaluated by an exact numerical method. It is found that the decay behavior of an excited atom can be fundamentally changed by the variation of the atomic position: Weisskopf-Wigner and non-Weisskopf-Wigner decay phenomena occur at different atomic positions in the PCs as a result of a significant difference in the local coupling strength. Our finding implies that it is possible to engineer the luminescence spectrum by controlling the atomic position.

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PubMed2002

Decay distribution of spontaneous emission from an assembly of atoms in photonic crystals with pseudogaps.

Spontaneous decay behaviors from an assembly of atoms (or molecules) in 3D photonic crystals (PC's) with pseudogaps are investigated. Theoretically, a lifetime distribution function for these atoms or molecules is defined to reveal decay kinetics. Our calculations show that quite wide or narrow lifetime distributions can occur for different spread configurations of the atoms (or molecules). The pure PC effect may lead to coexistence of both accelerated and inhibited decay processes. These results provide theoretical clarification for substantial discrepancies in the recent reported experiments.

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