Engineering topics
Peng, Zhang
Publications and source records attributed to Peng, Zhang.
Excitation of a slow wave structure
The Green's function on a slow wave structure is constructed. The Green's function includes all radial modes, and for each radial mode, all space harmonics. We compare the analytic solution of the frequency response on the slow wave structure with that obtained from a particle-in-cell code. Favorable comparison is obtained when the first few lower order modes are resonantly excited. This gives some confidence in the prediction of converting a pulse train into radiation using a slow wave structure.
Fe-doped InN layers grown by molecular beam epitaxy
Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN.
Stable heteronuclear few-atom bound states in mixed dimensions
We study few-body problems in mixed dimensions where two or three heavy atoms are trapped individually in parallel one-dimensional tubes or two-dimensional disks and a single light atom travels freely in three dimensions. Using the Born-Oppenheimer approximation, we find three- and four-body bound states for a broad parameter region. Specifically, the existence of trimer and tetramer states persists to the negative scattering length regime, where no two-body bound state is present. As pointed out by Y. Nishida in an earlier work [Phys. Rev. A 82, 011605(R) (2010)], these few-body bound states are stable against three-body recombination due to geometric separation. In addition, we find that the binding energy of the ground trimer and tetramer state reaches its maximum value when the scattering lengths are comparable to the separation between the low-dimensional traps.
Diffraction of Bose-Einstein condensates in quantized light fields
We investigate the atomic diffraction of Bose-Einstein condensates in quantized light fields. Situations in which the light fields are in number states or coherent states are studied theoretically. Analytical derivation and numerical calculation are carried out to simulate the dynamics of the atomic motion. In the condition that atoms are scattered by light in the number states with imbalanced photon-number distribution, the atomic transitions between different momentum modes would sensitively depend on the transition order and the photon-number distribution. The number-state nature of the light fields modifies the period of atomic momentum oscillations and makes forward and backward atomic transitions unequal. For light fields in coherent states, whether or not the intensities of the light fields are balanced, the atomic diffraction is symmetric and independent of the transition order.