Effects of atmosphere visibility on performances of non-line-of-sight ultraviolet communication systems

Dependence of performances of non-line-of-sight (NLOS) solar-blind ultraviolet (UV) communication systems on atmosphere visibility is investigated numerically by correlating the propagation of UV radiation with the visibility. A simplified solar-blind UV atmospheric propagation model is introduced, and the NLOS UV communication system model is constituted based on the single scattering assumption. Using the model, numerical simulation is conducted for two typical geometry configurations and different modulation formats. The results indicate that the performance of the NLOS UV communication system is insensitive to variation of visibility in quite a large range, and deteriorates significantly only in very low-visibility weather, and is also dependent on the geometry configuration of the system. The results also show that the pulse position modulation (PPM) is preferable due to its high-power efficiency to improve the system performance. (c) 2007 Elsevier GmbH. All rights reserved.

LD 侧面抽运Nd :YAG陶瓷激光器运转条件下归一化热参数优化理论及实验研究

The suppressing effect of laser extraction on the non-radiation transition process is taken into account when the heat model of gain media is developed. Based on the developed heat model, the heat generation in the operating LD side-pumped Nd: YAG ceramic lasers is quantified through using the normalized heating parameter, which can be deduced from the experimental results of the slope efficiency and the absorbed pumping power of the gain media. The main factors which influence on the heat generation are investigated by studying the normalized heating parameter, and the results show that the changes of the laser extraction efficiency, the beam overlap efficiency and the Nd3+ concentration will result in obvious variations of the normalized heating parameter. In this work, the laser extraction efficiency increases to 0.905 by the optimization of the transmission of the output coupling, and the normalized heating parameter decrease to 0.474, correspondingly.

Dual-wavelength competitive output in Nd:Y3Sc1.5Al3.5O12 ceramic disk laser

In this paper, we demonstrated a dual-wavelength competitive output in Nd:Y3SC1.5Al3.5O12 ceramic disk laser. Different dual-wavelength output behaviors for Nd:YSAG and Nd:YAG ceramic disk laser were investigated and discussed. By applying the energy transfer model, we suggested the reasonable explanation for this new phenomenon as the disordered replacing of Al3+ ions by Sc3+ ions. The main advantage of the dual-wavelength ceramic laser is the possibility to serve as the seed source to generate Terahertz radiation. (C) 2008 Elsevier B.V. All rights reserved.

Formation, thermal, optical and physical properties of GeS2-Ga2S3-AgCl novel chalcohalide glasses

Novel GeS2-Ga2S3-AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS2-Ga2S3-AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45-12.5 mu m). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (lambda(vis)) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H (v) , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS2-Ga2S3-AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.

Broadband infrared luminescence from bismuth-doped GeS2-Ga2S3 chalcogenide glasses

Near-infrared luminescence is observed from bismuth-doped GeS2-Ga2S3 chalcogenide glasses excited by an 808 nm laser diode. The emission peak with a maximum at about 1260 nm is observed in 80GeS(2)-20Ga(2)S(3):0.5Bi glass and it shifts toward the long wavelength with the addition of Bi gradually. The full width of half maximum (FWHM) is about 200 nm. The broadband infrared luminescence of Bi-doped GeS2-Ga2S3 chalcogenide glasses may be predominantly originated from the low valence state of Bi, such as Bi+. Raman scattering is also conducted to clarify the structure of glasses. These Bi-doped GeS2-Ga2S3 chalcogenide glasses can be applied potentially in novel broadband optical fibre amplifiers and broadly tunable laser in optical communication system.

Growth studies of m-GaN layers on LiAlO2 by MOCVD

This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical vapour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at similar to 3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate.

Studies of magnetic interactions in Mn-doped β-Ga2O3 from first-principles calculations

The magnetic behavior of Mn-doped beta-Ga2O3 is Studied from first-principles calculations within the generalized gradient approximation method. Calculations show that ferromagnetic ordering is always favorable for configurations in which two Mn ions substitute either tetrahedral or octahedral sites, and the ferromagnetic ground state is also sometimes favorable for configurations where one Mn ion substitutes a tetrahedral site and another Mn ion substitutes an octahedral site. However, the configurations of the latter case are less stable than those of the former. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Studies of magnetic interactions in Ni-doped ZnO from first-principles calculations

The magnetic interactions in Ni-doped ZnO are calculated using GGA and GGA + U method of density functional theory. The following three cases: (i) Ni-doped ZnO, (ii) (Ni, Al)-codoped ZnO, and (iii) (Ni, Li)-codoped ZnO are studied. The ferromagnetic ordering is always favorable for the three cases within GGA method. However, the ferromagnetic state is sometimes favorable after treating within the method of GGA + U. The GGA underestimates the correlated interactions especially when the Ni ions align directly to each other. (C) 2007 Elsevier B.V. All rights reserved.