Low-pressure mercury lamp pumped atomic iodine laser of high efficiency

For single pulse operation it was demonstrated that a low-pressure mercury lamp can successfully pump the atomic iodine laser using the active medium CF₃I. For a 22 ms long pump pulse an output energy of 100 mJ emitted over the same time duration was obtained. Measured oscillator efficiency was 0.54%. With respect to stored optical energy an efficiency of 1.6% was realized, a value not obtained so far with any other pump source. Application to pulsed high repetition rate or cw-operation seems possible at equal or even better efficiency.     

Modeling the warm-up phase of a high-pressure-lamps lightingnetwork

This work presents a study of the dynamic regime of a lamp-network interaction corresponding to the warm-up phase of a high-pressure mercury discharge lamp. The lamp's behavior is described by a variable pressure model using the local thermodynamic equilibrium (LTE) concept. Indeed, this model covers the most interesting phase of the network dynamic regime, where discharge lamps appreciably impose their nonlinearity. We first analyze the electrical behavior of the discharge lamp in a single phase circuit, taking into account the ballast saturation. Then a micronetwork is studied and are show the influence of the discharge's evolution on currents in phases and neutral conductors. Finally, from the results of the physical model, we set up a simple parametric modeling which reproduces the electrical behavior of the lamp during its warm-up phase. Such an approach can be useful for electrical engineers working on the discharge supply circuits at industrial frequency (50-60 Hz)     

Superconducting high pressure phase of germane

High-pressure structures of germane (GeH4) are explored through ab initio evolutionary methodology to reveal a metallic monoclinic structure of C2/c (4 molecules/cell). The C2/c structure consists of layerlike motifs containing novel "H2" units. Enthalpy calculations suggest a remarkably wide decomposition (Ge+H2) pressure range of 0-196 GPa, above which C2/c structure is stable. Perturbative linear-response calculations for C2/c GeH4 at 220 GPa predict a large electron-phonon coupling parameter lambda of 1.12 and the resulting superconducting critical temperature reaches 64 K.     

Absorption and emission lines of a mercury molecule in a mercury discharge lamp

Absorption lines are revealed in spectra of a mercury discharge lamp (Planck’s radiator). Some of the lines were identified by Lord Rayleigh as the absorption lines of a Hg₂ molecule. New absorption lines at 253.29, 253.53, 253.76, and 254.20 nm, as well as emission lines at 264.80, 254.96, 265.11, 279.89, 288.82, 301.50, 301.74, and 301.95 nm are discovered, which enabled the construction of a diagram of the lower excited electronic states of a mercury molecule. It is demonstrated that the dips in the intensity profiles of the atomic mercury lines at 253.65, 435.83, 404.65, and 546.07 nm arise from the radiation absorption in vibronic transitions of diatomic Hg₂ molecules. The concentration of mercury molecules in the plasma of mercury discharge lamps is determined to be of the order of 10⁸ cm^?3. However, their contribution to the formation of the emission line profiles is essential due to the multiple radiation passage through the emitting plasma.     

锗烷（GeH4）的高压超导相

通过从头算演化理论的结构预测方法,文章作者提出了GeH4的一个高压金属相结构（单斜C2/c）.这一结构包含奇特的“H2” 单元. 焓的计算结果表明,GeH4 在压力低于196 GPa时分解为单质Ge 和H2, 而在高于这一压力时C2/c结构稳定存在.在220 GPa压力下, 线性响应微扰理论的计算结果表明,C2/c结构的电子-声子相互作用参数为1.12, 其超导转变温度达到64 K.     

Kinetics of phase transitions under high pressure

Abstract

Phase transitions under high pressure have attracted increasing attention i n connection with high pressure synthesis of new materials (e.g. superhard materials, ceramics, semiconductors, high temperature superconductors) and the exploration of geological processes like the formation of rocks and minerals. For t h e investigation of thermodynamic and electronic equilibrium properties a broad spectrum of methods for pressure generation and physical measurements have been developed ^1,2,3,4. Tha measurement of equilibrium properties, however, gives only poor insight into the detailed mechanisnts of phase changes. The accurate determination of phase equilibria and phase diagrams becomes inore and more difficult a t low temperatures due to increasing hysteresis effects end t h e extrapolation of experimental data to zerc, teiiipwature a nd the compar ison with quantumiiiechanical ah in.itio calculations are questionable.     

锗烷(GeH4)的高压超导相

通过从头算演化理论的结构预测方法,文章作者提出了GeH4的一个高压金属相结构(单斜C2/c),这一结构包含奇特的"H2"单元.焓的计算结果表明,GeH4在压力低于196 GPa时分解为单质Ge和H2,而在高于这一压力时C2/c结构稳定存在.在220 GPa压力下,线性响应微扰理论的计算结果表明,C2/c结构的电子一声子相互作用参数为1.12,其超导转变温度达到64 K.     

Laser action of Na2 molecules in a sodium high pressure discharge lamp

Rutherford backscattering has been used to measure the lattice positions occupied by Pb following room temperature implantation into silicon. The data provide information on the size and deposition of amorphous zones in relation to the distribution of implanted Pb.     

CrI_3高压相变及其光学性质理论研究

利用第一性原理计算方法,探讨了体相CrI_3在低温斜方六面体结构(■,BiI_3-type)及高压单斜结构(C2/m,AlCl_3-type)的相变、电子结构和光学性质.计算结果显示,半导体CrI_3当压强增加到26.1GPa时,高压导致的晶格畸变致使CrI_3从相■变化到相C2/m;原子之间的错位位移,使导带处的能带发生下移,价带处的能带发生了一定程度的上移,导致带隙减小.两种相的光学性质进一步验证了这些特性.     

Acceleration of re-ignition of high pressure mercury discharge lamps using photo-pre-ionization

High Intensity Discharge (HID) lamps are difficult to re-ignite rapidly because of the high pressure of metal vapor at high temperatures. We have succeeded in reducing the re-ignition time of high-pressure mercury lamps by using a pre-ionization step where an excess of electrons are generated by UV laser irradiation into the lamp. The effect of changing the laser focal point of the UV laser in the lamp and the position of an auxiliary electrode were also investigated. The time interval for re-ignition was reduced from 230s to 100s by laser irradiation near to the cathode. The results clearly showed that the effect of accelerating the re-ignition time by the pre-ionization step was determined by the behavior of excess electrons generated during the UV laser irradiation.     

Specific heat of the superconducting high pressure phase Ga II

The high pressure modification gallium II, which becomes superconducting near 6.4 K, has for the first time been investigated calorimetrically at about 35 kbar in the temperature range of liquid helium. From the data a Debye temperature _D = 178K and an electronic specific-heat coefficient =1.75 mJ/mole K² are obtained. These values are in good qualitative accord with the increased superconductingT _c with respect to that of Ga I.Work supported by the Deutsche Forschungsgemeinschaft.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday.     

Crystalline post-quartz phase in silica at high pressure

alpha-quartz, which has been reported to undergo pressure-induced amorphization, was found to transform to a monoclinic, crystalline phase when compressed to 45 GPa at room temperature in a close to hydrostatic, helium pressure medium. The x-ray powder diffraction data obtained could be indexed based on a monoclinic cell, and the intensities are in agreement with a P2(1)/c model structure built up of 3x2 zigzag chains of SiO6 octahedra. This new polymorph of silica, which is metastable under ambient conditions, has been isolated for the first time and is one of several possible competing dense forms containing octahedrally coordinated silicon.     

Deformation phase transition in vanadium under high pressure

Within the framework of the Landau theory of phase transitions and the density functional method, it is shown that the structural transformation from a body-centered cubic phase to a rhombohedral phase revealed in vanadium at 69 GPa is a first-order deformation phase transition close to a second-order phase transition.     

A high pressure Raman study of KTP and pressure induced phase transitions

Potassium titanate orthrophosphate KTiOPO₄ (KTP) has been studied by high pressure Raman technique to 17 GPa using a diamond cell. The Raman data reveal that two phase transitions occur in the system: one near 5.5 GPa and another near 10 GPa. The Lower-pressure transition is definitely first-order but appears to be driven by the phonon mode near 56 cm⁻¹, which exhibits marked softening. A mean field-like behavior is observed. It is hypothesized that this transition is likely to be from ferroelectric (FE) to an antiferroelectric (AF) phase. The 10 GPa transition may be due to AF-PE (paraelectric) transition driven by pressure from high temperature to room temperature. From the larger pressure responce of the PO₄ vibrational modes it is believed that the PO₄ polyhedral compression is larger than the TiO₆ polyhedral compression. leading to polyhedral tilt transitions.     

Semiconductor-metal phase transition in LaBi under high pressure

Physics of the Solid State - The effect of pressure up to 22 GPa on the electrical resistance and thermopower of lanthanum monobismuthide at room temperature has been studied. A semiconductor-metal...