Analysis of the laser performance of Tm3+, Tb3+(Ho3+):YVO4 crystals at ～1.5μm wavelength

The absorption spectra of Tb,Tm:YVO_4 and Ho,Tm:YVO_4 are measured. The radiant and non-radiant transition probabilities from higher level to lower level, A_{i,j} and ω_{i,j}, and the cross-elaxation probability are calculated in virtue of Judd－Ofelt and Dexter theories. The fluorescence lifetime of Tm^{3+} in the Tb^{3+} (or Ho^{3+}) co-doped crystal is calculated. It indicates that the lifetime of initial level {}^3H_4 of the laser transition can be shorter than that of terminal level {}^3F_4 of the transition if the atomic percentage of Tb^{3+} (or Ho^{3+}) ions is bigger than about 1 at%: namely, by means of the co-doping Tb^{3+} (or Ho^{3+}) ions the self-termination phenomenon of laser light can be eliminated. Inserting the optic parameters to the formula deduced here on the laser threshold power P^{(4)}_{th} and the slope efficiency η^{(4)}_s of the four-energy-level system, we obtain the relationship of threshold power P^{(4)}_{th} to the concentration of Tm^{3+} ions and discuss the effect of Tb^{3+} (or Ho^{3+}) ion concentration on the laser threshold power P^{(4)}_{th} around 1.5μm wavelength. The result shows that Tb,Tm:YVO_4 crystal is a better choice to make the laser at ～1.5μm wavelength than Ho,Tm:YVO_4 crystal. We give the appropriate composition of (1－2) at% Tb, (1－2) at% Tm:YVO_4, just for reference.     

Investigation of fabrication and hetero-epitaxy relationship of CoCrPt thin films grown on CrW underlayer

This paper reports that longitudinally oriented CoCrPt thin films with Cr₈₅W₁₅ underlayer and CoCr intermediate layer for use of giant magnetoresistance heads were fabricated by magnetron sputtering. Without CoCr intermediate layer, CoCrPt layer deposited directly on Cr₈₅W₁₅ underlayer which has a dominant (200) texture exhibits unexpected (10\bar {1}1) texture. After introducing CoCr intermediate layer, the CoCrPt layer shifts into (11\bar {2}0) texture. This article studies the crystallographic hetero-epitaxy relationship between magnetic layer and underlayer in order to understand the appearance of CoCrPt (10\bar {1}1) texture on (200) textured Cr underlayer and the influence of CoCr intermediate layer on the inducement of CoCrPt (11\bar {2}0) texture. The CoCr intermediate layer plays a crucial role in controlling the microstructure and consequently the magnetic properties of the overlying magnetic layer.     

Magnetic properties and coercivity mechanism of precipitation-hardened Gd－Co based ribbons

Gd(Co_{0.88-x}Cu_xFe_{0.09}Zr_{0.03})_z ribbons with x=0.075-0.200 and z=6.4－7.7 have been prepared by a melt-spinning technique. A cellular microstructure consisting of 2:17 cells surrounded by the 1:5 cell boundary phase is obtained after precipitation hardening. The dependence of room temperature coercivity on the heat treatment process suggests that the long-time isothermal aging is not helpful for the development of magnetic properties. Positive temperature coefficient of remanence from room temperature to about 673K is typical for all samples, while positive temperature coefficient of coercivity is obtained only in ribbons with low Cu content. The coercivity mechanism of the precipitation-hardened ribbons at different temperatures is also discussed.     

Investigations on spectroscopic parameters, vibrational levels, classical turning points and inertial rotation and centrifugal distortion constants for the X1∑+g state of sodium dimer

The density functional theory (B3LYP, B3P86) and the quadratic configuration-interaction method including single and double substitutions (QCISD(T), QCISD) presented in Gaussian03 program package are employed to calculate the equilibrium internuclear distance $R_{\rm e}$, the dissociation energy $D_{\rm e }$ and the harmonic frequency $\omega _{\rm e}$ for the $X{}^{1}\Sigma^{ + }_{\rm g}$ state of sodium dimer in a number of basis sets. The conclusion is gained that the best $R_{\rm e}$, $D_{\rm e}$ and $\omega _{\rm e}$ results can be attained at the QCISD/6-311G(3df,3pd) level of theory. The potential energy curve at this level of theory for this state is obtained over a wide internuclear separation range from 0.16 to 2.0~nm and is fitted to the analytic Murrell--Sorbie function. The spectroscopic parameters $D_{\rm e}$, $D_{0}$, $R_{\rm e}$, $\omega _{\rm e}$, $\omega _{\rm e}\chi _{\rm e}$, $\alpha _{\rm e}$ and $B_{\rm e}$ are calculated to be 0.7219~eV, 0.7135~eV, 0.31813~nm, 151.63~cm$^{ - 1}$, 0.7288~cm$^{ - 1}$, 0.000729~cm$^{ - 1}$ and 0.1449~cm$^{ - 1}$, respectively, which are in good agreement with the measurements. With the potential obtained at the QCISD/6-311G(3df,3pd) level of theory, a total of 63 vibrational states is found when $J=0$ by solving the radial Schr\"{o}dinger equation of nuclear motion. The vibrational level, corresponding classical turning point and inertial rotation constant are computed for each vibrational state. The centrifugal distortion constants ($D_{\upsilon }\, H_{\upsilon }$, $L_{\upsilon }$, $M_{\upsilon }$, $N_{\upsilon }$ and $O_{\upsilon })$ are reported for the first time for the first 31 vibrational states when $J=0$.     

Study of second-order nonlinear hyperpolarisability of all-trans-β-carotene in solutions by linear spectroscopic technique

This paper demonstrates the second-order nonlinear hyperpolarisability \gamma of all-trans-β-carotene in different solvents by linear spectroscopic technique that is based on resonance Raman scattering and UV--VIS (Ultraviolet-visible) absorption spectroscopy. Owing to the two-level model well describing the link that exists between the resonance Raman scattering and stimulated Raman scattering, the stimulated Raman polarisability α_{\rm R} can be calculated through the two-photon resonance system. The value of \gamma of all-trans-β-carotene in carbon bisulfide solution is 6.435\times 10^{-33} esu (1~esu of resistance =8.98755\times10^{11}~\Omega) that is close to the true value, because the solution of all-trans-β-carotene in carbon bisulfide satisfies the rigid resonance Raman scattering condition. This method is expected to be worthy of applications to measure the second-order nonlinear hyperpolarisability of a conjugate organic molecule.     

The mechanism research of the Cr^4＋Nd^3＋：YAG laser

The 946nm diode-pump microchip self-Q-switched laser of a chromium and neodymium codoped yttrium aluminum garnet crystal material (Cr^{4+}Nd^{3+}:YAG) is studied, especially about its physical mechanism of operation. The {}^4F_{3/2}→{}^4I_{9/2} transition of Nd^{3+} ion is beneficial to achieving laser oscillation in a quasi-three-level system based on coating the cavity mirrors of the microchip with films that suppress the 1064nm operation and enhance the 946nm laser. The Cr^{4+} ion is a saturable absorber. The initial loss N_{t1} is high, which acts as the threshold for laser oscillation. The stable loss N_{t2} is low because the Cr^{4+} ion is acceleratively bleached by the fast enhancement of the oscillating laser. The high N_{t1}, small N_{t2} and fast progresses permit the oscillating laser of the Cr^{4+}Nd^{3+}:YAG to have a good self-Q-switched property whose full width at half maximum is about 4.2ns. Its highest laser power is about 5.7mW. Its peak power is about 150W. Its good fundamental transverse TEM_{00} mode results from the absorption bleaching established by both the pump and oscillating lasers, which suppress other transverse mode and allow the oscillation only in the fundamental transverse TEM_{00} mode.     

Magnetic-Field-Induced Strains of Bonded Ni-Mn-Ga Melt-Spun Ribbons

Non-stoichiometric Ni50Mn27 Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magneticfield-induced strain （MFIS） of Ni-Mn-Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained. The experimental results show that Ni50Mn27Ga23 bonded ribbons exhibit a typical thermal-elastic shape memory effect in the thickness direction. The martensitic transformation strain of bonded ribbons is an expansive strain of about 0.3% without the magnetic field and a contractive strain of about -0.46% at the magnetic field of 1 T. The field can not only enhance the value of the martensitic transformation strain of the bonded ribbons, but can also change the direction of the strain. The bonded ribbons alloy presents negative MFIS and obtains a larger value of the strain though influenced by the adhesive between the ribbons. Therefore, the preparation technique of the Ni-Mn-Ga bulk alloy by bonding melt-spun ribbons is helpful to get rid of the size restriction of the ribbon and to broaden the applications of the ribbons.     

Diagnosing holographic type dark energy models with the Statefinder hierarchy,composite null diagnostic and w-w′pair

The main purpose of this work is to distinguish various holographic type dark energy(DE) models, including the ΛHDE, HDE,NADE, and RDE model, by using various diagnostic tools. The first diagnostic tool is the Statefinder hierarchy, in which the evolution of Statefinder hierarchy parmeter S_3~(1)(z) and S_4~(1)(z) are studied. The second is composite null diagnostic(CND), in which the trajectories of {S_3~(1),.} and {S_4~(1),.} are investigated, where. is the fractional growth parameter. The last is w-w′analysis, where w is the equation of state for DE and the prime denotes derivative with respect to lna. In the analysis we consider two cases: varying current fractional DE density Ω_(de0) and varying DE model parameter C. We find that:(1) both the Statefinder hierarchy and the CND have qualitative impact on ΛHDE, but only have quantitative impact on HDE.(2) S_4~(1) can lead to larger differences than S_3~(1), while the CND pair has a stronger ability to distinguish different models than the Statefinder hierarchy.(3)For the case of varying C, the {w,w′} pair has qualitative impact on ΛHDE; for the case of varying Ω_(de0), the {w, w′} pair only has quantitative impact; these results are different from the cases of HDE, RDE, and NADE, in which the {w,w′} pair only has quantitative impact on these models. In conclusion, compared with HDE, RDE, and NADE, the ΛHDE model can be easily distinguished by using these diagnostic tools.     

Relationship between the magnetic field distribution and attractive force of single-domain YBCO bulk under different field cooling processes

The levitation forces under different field cooling states were measured at 77K by changing the field cooling distance Z_{fc} between a YBCO bulk and a permanent magnet. It is found that the relationship between the absolute maximum attractive force (Z_{maf}) and the corresponding gap distance (Z_{maf}) to F_{maf} can be well described by exponential laws as a function of Z_{fc}, which allow us to predict these values according to Z_{fc}. It is also found that the distance between the Z_{0fa} (gap distance corresponding to the zero force) and Z_{maf} in the ascending process is a constant value, which is closely related to the constant reduction factor of the axial component of flux density along the axial line of the magnet if Z_{maf}-Z_{0fa} is a constant value. These results are very interesting for fundamental research and helpful in practical designing and applications.     

Electron Backscattered Diffraction of Transgranular Crack Propagation in Soft Steel

We consider the crack propagation in a soft steel sheet during the formation. The drawability is considered in relation with the structural anisotropy, the mechanical behaviour is related to both the grain morphology and the texture. The structure heterogeneity could lead to the apparition of micro-cracks. The results show the texture effect on the crack propagation and on the crack arrest in soft steel during the formation. The EBSD technique allows to show that the adjustment of the grain orientation from the initial main component {111}（112） towards the deformation orientation {111}（110） incites a trans-granular crack through a grain with initial {111}（112） orientation in a globally ductile material. It is the presence of grains with {111}（110） orientation which permits the closing of micro-cracks.     

Role of Barrier Modification and Nuclear Structure Effects in Sub-Barrier Fusion Dynamics of Various Heavy Ion Fusion Reactions

The role of barrier modifications and the relevant nuclear structure effects in the fusion of the \( {}_8{}^{16}O+{}_{62}{}^{144,148,150,152,154}Sm \) and \( {}_3{}^{6,7}Li+{}_{62}{}^{152}Sm \) systems is analyzed within the context of the energy-dependent Woods-Saxon potential model (EDWSP model) and the coupled channel model. For the \( {}_8{}^{16}O+{}_{62}{}^{144,148,150,152,154}Sm \) reactions, where the colliding pairs are stable against breakup, the collective excitations and/or static deformations are sufficient to account for the observed fusion enhancement. In contrast, the model calculations overpredict the complete fusion data at above - barrier energies for the \( {}_3{}^{6,7}Li+{}_{62}{}^{152}Sm \) systems, where the importance of projectile breakup effects has been pointed out. Due to the low threshold of the alpha-breakup channel, the weakly bound projectiles \( \left({}_3{}^{6,7}Li\right) \) break up into charged fragments before reaching the fusion barrier and consequently the complete fusion cross section is suppressed by 28% (25%) in the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction with respect to predictions of coupled channel calculations. However, the EDWSP model based calculations can minimize the suppression factor by as much as of 13% (8%) in the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction with reference to the predictions made by the coupled channel calculations. Therefore, the complete fusion data of the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction at above - barrier energies is reduced by 15% (17%) with respect to the expectations of the EDWSP model. The extracted suppression factors for the studied reactions are due to the modifications of the barrier profile as a consequence of the energy - dependence in nucleus-nucleus potential, and thus greater barrier modifications occur for more weakly bound system, which in turn, confirms the breakup of projectile in the incoming channel.     

Structural,microstructural and magnetic properties of nanocomposite isotropic Sm(CobalFe0.1MyZr0.04B0.04)7.5 ribbons with M=Ni,Cu and y=0.09 and 0.12

In boron-substituted melt-spun Sm(Co,Fe,Cu,Zr)_7.5-type alloys a nanocomposite microstructure and high coercivities in both as-spun and short-time annealed ribbons can be obtained. In the present study three different compositions, namely Sm(Co_0.73Fe_0.1Cu_0.09Zr_0.04B_0.04)_7.5, Sm(Co_0.70Fe_0.1Cu_0.12Zr_0.04B_0.04)_7.5 and Sm(Co_0.70Fe_0.1Ni_0.12Zr_0.04B_0.04)_7.5 have been examined in order to investigate the influence of composition on the magnetic properties and the microstructure. Melt-spun ribbons have been obtained and annealing has been followed under argon atmosphere for 30–75 min at 600–870 °C. For the as-spun ribbons the TbCu₇-type of structure and fcc-Co as a secondary phase have been identified in the X-ray diffraction patterns. For the annealed ribbons above 700 °C the 1:7 phase transforms into 2:17 and 1:5 phases. The TEM studies have shown a homogeneous nanocrystalline microstructure with average grain size of 30–80 nm. Coercivity values of 15–27 kOe have been obtained from hysteresis loops traced in non-saturating fields. The coercivity decreases with temperature, but it is sufficiently large to maintain values higher than 5 kOe at 380 °C.     

Stark spectroscopy of high-lying odd parity levels in atomic samarium

We have performed a series of experiments to observe 11 Stark-induced E1 transitions from the 15650.55 cm^-1 level to higher levels with odd parity in samarium (Sm) with optical double-resonance technique. Five Stark-induced E1 transition to the 28233.08, 28613.22, 28913.97, 29041.31 and 29130.03 cm^-1 levels have been observed. In order to investigate the contributors to the Stark-induced E1 transition, we have measured scalar and tensor polarizabilities for the observed Stark-induced E1 transitions. Clear Stark splittings were observed for the levels 28233.08 and 28613.22 cm^-1, and their tensor polarizabilities were determined for each isotope. Scalar polarizabilities were determined for the 28233.08, 28613.22, 28913.97 and 29130.03 cm^-1 levels for the first time. Among them, scalar polarizability for the 28233.08 cm^-1 level was the largest in magnitude and was 3.60(10) x 10³ kHz/(kV/cm)² for Sm. We noticed that both scalar and tensor polarizabilities of the 28233.08 cm^-1 level depend on the isotope; the difference of magnitude of the scalar and tensor polarizabilities between Sm and Sm were remarkably large and were about 10 and 6 percent, respectively.Received: 10 February 2003, Published online: 30 July 2003PACS: 32.60.+i Zeeman and Stark effects - 32.10.Dk Electric and magnetic moments, polarizabilityD. Angom: Present address: Physical Research Laboratory, Navarangpura, Ahmedabad 380 009, India.     

用H-W-ECR CVD系统实现氢化非晶硅薄膜在氢气环境下同时进行化学热退火和光诱导退火的研究

为了研究氢化非晶硅薄膜的稳定性，我们设计了一个在原子氢气氛中热退火的同时进行光诱导退火的实验(TLAH)。实验装置是由传统的微波电子回旋共振化学气相沉积系统改造而成为热丝辅助微波电子回旋共振化学气相沉积系统。为了对这一退火方法进行比较，对样品还进行了热退火、热退火同时进行光诱导退火。同时，为了定量地分析光电导衰退，我们假设光电导衰退遵循扩展指数规律：1/σph=1/σs-(1/σs-1/σ0)exp[-(t/τ)β]，这里扩展指数参数β 和时间常数 τ 可从与 lnt 的线性关系中截距和斜率得到, 式中光电导饱和值σs可以通过在对数坐标系中表示的光电导和光照时间关系进行高斯拟合得到。实验结果显示：TLAH 方法可以提高氢化非晶硅薄膜的稳定性、改善其微结构和光电特性，同时还发现，光学带隙明显减小、荧光光谱显著地朝着低能方向移动。     

Observational constraints on the accelerating universe in the framework of a 5D bounce cosmological model

In the framework of a five-dimensional (5D) bounce cosmological model, a useful function f(z) is obtained by giving a concrete expression of deceleration parameter q(z)=q₁+{q₂}/{1+ln (1+ z)}. Then using the obtained Hubble parameter H(z) according to the function f(z), we constrain the accelerating universe from recent cosmic observations: the 192 ESSENCE SNe Ia and the 9 observational H(z) data. The best fitting values of transition redshift z_T and current deceleration parameter q₀ are given as z_T= 0.65_-0.12^0.25 and q₀ = - 0.76_-0.15^+0.15 (1σ). Furthermore, in the 5D bounce model it can be seen that the evolution of equation of state (EOS) for dark energy w_de can cross over -1 at about z=0.23 and the current value w_0de= - 1.15<- 1. On the other hand, by giving a concrete expression of model-independent EOS of dark energy w_de, in the 5D bounce model we obtain the best fitting values z_T= 0.66_0.08^+0.11 and q₀ = - 0.69_0.10^+0.10 (1σ) from the recently observed data: the 192 ESSENCE SNe Ia, the observational H(z) data, the 3-year Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital Sky Survey (SDSS) baryon acoustic peak and the x-ray gas mass fraction in clusters.     

Mono-top signature from stop decay at the HE-LHC

Searching for the top squark(stop)is a key task to test the naturalness of SUSY.Different from stop pair production,single stop production relies on its electroweak properties and can provide some unique signatures.Following the single production process pp→t^~1X(~)1→tX^~1⁰X^~1^-,the top quark has two decay channels:leptonic channel and hadronic channel.In this paper,we probe the observability of these two channels in a simplified minimal supersymmetric standard model scenario.We find that,at the 27 TeV LHC with the integrated luminosity of L=15 ab^-1,mt^-1<1900 GeV andμ<750 GeV can be excluded at 2σthrough the leptonic mono-top channel,while m_t^-1<1200 GeV andμ<350 GeV can be excluded at 2σthrough the hadronic channel.     

Magnetic properties and microstructure of melt-spun Sm(Co,Fe,Cu,Zr)8 magnets

We report on the microstructural and magnetic properties of rapidly quenched Sm(Co_balFe_0.1Cu_xZr_0.04)₈ ribbons. Samples spun at velocities above 40 m/s are nanocrystalline and magnetically hard, even in the as-spun state. The coercivity and its temperature coefficient can be improved by annealing at 750°C. Samples spun at low speeds have low coercivity in the as-spun state and are characterized by larger grain sizes. By annealing a cellular precipitation structure within the grains, similar to that of bulk Sm(Co,Fe,Cu,Zr)_z magnets, can be obtained in Cu-containing samples, resulting in an increase of the coercivity, since the precipitates act as pinning centers. Some precipitation occurs even in as-spun Cu-free samples, indicating that their formation is not directly related to the existence of Cu, in contrast to the cellular structure. Compared to the bulk materials, lower annealing temperatures and shorter heat treatment times are required and the slow cooling process is not needed. The activation volumes for the magnetic reversal process are estimated by magnetic relaxation measurements.     

Studies on chargino production and decay at a photon collider

A Monte-Carlo analysis on production and decay of supersymmetric charginos at a future photon-collider is presented. A photon collider offers the possibility of a direct branching-ratio measurement. In this study, the process has been considered for a specific mSUGRA scenario. Various backgrounds and a parameterised detector simulation have been included. Depending on the centre-of-mass energy, a statistical error for the directly measurable branching ratio BR( ) of up to 3.5% can be reached.Received: 14 March 2005, Revised: 31 May 2005, Published online: 28 June 2005G. Klämke: Now at: Institut für Theoretische Physik, Universität Karlsruhe, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe, Germany