Spectrum of spin waves in cold polarized gases

The spin dynamics of cold polarized gases are investigated using the Boltzmann equation. The dispersion relation for spin waves (transverse component of the magnetic moment) and the spin diffusion coefficient of the longitudinal component of the magnetic moment are calculated without using fitting parameters. The spin wave frequency and the diffusion coefficient for rubidium atoms are estimated numerically.     

Conditions for the existence of interface spin waves in a biferromagnetic interface

The eigenproblems of interface spin waves of a (100) biferromagnetic interface are solved exactly by use of the interface rescaling approach. Particularly, the necessary and sufficient conditions for the existence of interface spin waves are obtained analytically.Received: 24 June 2003, Published online: 2 October 2003PACS: 75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures) - 75.30.Ds Spin waves - 75.10.Jm Quantized spin modelsG.H. Yun: ndkjc7@imu.edu.cn     

Broadband nonreflecting properties of thin inhomogeneous coatings for arbitrarily polarized electromagnetic waves in a wide range of angles of incidence

In the electrodynamics of inhomogeneous dielectrics, a new model that allows an exact solution is proposed. The fields of s-and p-polarized waves are determined for the case of their propagation through a layer with a monotonic distribution of the dielectric constant, as well as with a nonmonotonic distribution characterized by two free parameters. Inhomogeneous coatings of this kind are shown to exhibit nonreflecting properties under arbitrarily polarized waves incident at arbitrary angles.     

A wide angle neutron spin filter system using polarized He

Polarized ³He neutron spin filters can operate over a wide neutron energy range and provide a large angular acceptance. A compact ³He neutron spin filter system has been developed for the Multi-Axis Crystal Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Sealed ³He cells, polarized by spin-exchange optical pumping, are used as polarizer and analyzer. The polarization of the neutrons incident on the sample is inverted by flipping the polarization of the ³He gas in the polarizer, with only a small effect on the analyzer cells. The cell fabrication process, ³He spin flipper, and the holding magnetic field are discussed and we present the results of a first on-linetest.     

Energy transport for ion acoustic waves in a spin polarized quantum plasma

The separate spin evolution quantum hydrodynamics(SSE-QHD) model is used to investigate the energy behavior for ion acoustic waves in degenerate quantum plasma. Numerical results show that the energy flow speed decreases with spin polarization parameter. It is also shown that it decreases with the increasing rate up to a certain range of wave number and then it goes to zero asymtotically. It is observed that Bohm potential suppresses the energy flow speed. It is also noticed that the energy flow speed deviates from the group velocity even in the absence of Bohm potential effect. However, the contribution of of Bohm poential effect in spin polarized plasma reduces the extent of deviation.     

Large amplitude spin waves in ultra-cold gases

We discuss the theory of spin waves in non-degenerate ultra-cold gases, and compare various methods which can be used to obtain appropriate kinetic equations. We then study non-hydrodynamic situations, where the amplitude of spin waves is sufficiently large to bring the system far from local equilibrium. The full position and momentum dependence of the distribution function must then be retained. In the first part of the article, we compare two general methods which can be used to derive a kinetic equation for a dilute gas of atoms (bosons or fermions) with two internal states (treated as a pseudo-spin 1/2). The collisional methods are in the spirit of Boltzmann's original derivation of his kinetic equation where, at each point of space, the effects of all sorts of possible binary collisions are added. We discuss two different versions of collisional methods, the Yvon-Snider approach and the S matrix approach. The second method uses the notion of mean field, which modifies the drift term of the kinetic equation, in the line of the Landau theory of transport in quantum liquids. For a dilute cold gas, it turns out that all these derivations lead to the same drift terms in the transport equation, but differ in the precise expression of the collision integral and in higher order gradient terms. In the second part of the article, the kinetic equation is applied to spin waves (or internal conversion) in trapped ultra-cold gases. Numerical simulations are used to illustrate the strongly non-hydrodynamic character of the spin waves recently observed with trapped ⁸⁷Rb atoms. The decay of the phenomenon, which takes place when the system relaxes back towards equilibrium, is also discussed, with a short comment on decoherence. In two appendices we calculate the Wigner transform of the interaction term in the S matrix method, to first order in gradients; Appendix A.1 treats the case of spin-independent interactions, Appendix A.2 that of spin-dependent interactions.Received: 17 April 2003, Published online: 17 July 2003PACS: 05.30.-d Quantum statistical mechanics - 51.10.+y Kinetic and transport theory of gases - 75.30.Ds Spin waves     

The temperature coefficients of delay of surface acoustic waves in LGS and LGN crystals in a wide temperature range

Numerical analysis of the first-and second-order temperature coefficients of the delay of surface acoustic waves (SAWs) in LGS and LGN crystals was carried out. The calculations were performed along thermostable directions in a wide temperature range. The effect of an aluminium layer having a finite thickness on the SAW temperature characteristics is shown.     

宽温度范围微型人眼安全激光器

报道了一种宽温度适应范围的微型化人眼安全激光器。采用中心波长940nm的二极管作为泵浦源,Er3+/Yb3+共掺磷酸盐玻璃作为增益介质,Co2+:MgAl2O4作为被动调Q晶体,研究了微型激光器的结构和激光在宽温度范围下的输出特性。当泵浦能量9mJ,重复频率10Hz,泵浦脉宽5ms时,获得了单脉冲能量130μJ,脉宽5.5ns,峰值功率大于20kW的激光输出,光束质量因子为1.3。采用真空封装工艺,在-40~50℃温度范围内,自然冷却方式下激光器稳定输出,功率不稳定性波动小于5%。     

宽温度范围微型人眼安全激光器

报道了一种宽温度适应范围的微型化人眼安全激光器。采用中心波长940 nm的二极管作为泵浦源,Er3+/Yb3+共掺磷酸盐玻璃作为增益介质,Co2+: MgAl2O4作为被动调Q晶体,研究了微型激光器的结构和激光在宽温度范围下的输出特性。当泵浦能量9 mJ,重复频率10 Hz,泵浦脉宽5 ms时,获得了单脉冲能量130 J,脉宽5.5 ns,峰值功率大于20 kW的激光输出,光束质量因子为1.3。采用真空封装工艺,在－40~50 ℃温度范围内,自然冷却方式下激光器稳定输出,功率不稳定性波动小于5%。     

A Teflon pressure-transducer-specimen bond for ultrasonic measurements over a wide temperature range

A major limitation for the application of megahertz ultrasonic techniques to the study of the properties of solids is the problem of finding transducer-specimen bonds useful over a wide temperature range. A Teflon pressure bond has been developed and tested. It appears to overcome most of the problems, and promises to allow for many studies previously more difficult or impracticable.     

Analytical approximation of the thermal and caloric equations of state for real gases over a wide density and temperature range

The thermal and caloric equations of state of the main components of gas mixtures normally used in calculations of gas dynamic processes, including combustion and detonation, as well as in problems of internal ballistics, are presented in an analytical form. The formulas obtained for the equations of state contain a relatively small number of parameters and provide an average error of approximation of less than 1% at temperatures from 500 to 2000–2500 K and densities up to the critical.     

Observation of the Goldanskii effect over a wide temperature range

The Goldanskii effect was observed in the recoilless absorption spectra of the 21.6 KeV gamma ray of ¹⁵¹Eu in Eu₂Ti₂O₇ between 4 and 900 K. Full agreement between the Goldanskii theory and the experimental spectra was obtained throughout the whole temperature range.     

组分调制Cu3NPdx的大温区恒定电阻率

单一固体材料的电阻率是关于温度的复杂函数.目前尚未见关于相当大的温度范围内恒定电阻率的报道;对恒电阻的需求仍然是通过材料结构组合或电路设计实现的.Cu3NPdx随组份的变化会经历半导体－半金属相变,在Cu3NPd0.238中可以在240K的温度范围内测得不变的电阻率. 这一发现至少表明大温区内恒电阻是可以在单一材料内实现的,它对固体物理的理解本身以及诸多应用都有重要的意义.     

A simple automatic ellipsometer for a wide energy range

We describe the design, construction and operation of an automatic ellipsometer based on a design similar to that of Archard, Clegg and Taylor. A simple calibration procedure eliminates all systematic errors in the analyzer-detector system. Data reduction is done with a modified version of the ellipsometric equations developed in the text.     

A Rb-magnetometer for a wide range and high sensitivity

A Rb-magnetometer was constructed for a wide range of application. It uses a very small optically pumped resonance cell with an active volume of less than 0.1 cm³ as the sensor element. The cell is housed in a small probe containing polarizer, rf-coil, heater and photoelement. The pumping light is brought to the resonance cell by use of a 3 m long fibre optics. The magnetometer allows continuous monitoring or stabilizing magnetic fields from about 3·10^?8T to beyond 0.3T. The ultimate sensitivity of the instrument is of the order of 10^?10T. Observing the Hanle signal in the transverse mode of optical pumping the instrument can be used for zero field detection and for the measurement for weak fields by means of field compensation.     

Spectroscopy of a plane-parallel axially symmetric plasma of wide temperature range

A pulsed discharge is localized with two parallel insulating plates having coaxial holes to produce a plasma of temperature range 5000 to 10⁵° K. The spectrum and structure of the plasma are reported.We are indebted to M; A; El'yashevich for interest in this work.     

Analysis of the actual Schottky-barrier contact model in a wide temperature and bias-voltage range

We numerically study the model of an actual metal-semiconductor Schottky-barrier contact with an interfacial layer and surface states (the Bardeen model). Our study is based on the previously developed view that the anomalies of the characteristics of such a contact is a consequence of the nonlinear dependence of the barrier height on the bias voltage. It is shown that on this basis it is possible to explain in a natural way the so-called low-temperature anomaly in metal-semiconductor Schottky-barrier contacts (an increase in the ideality factor of the current-voltage characteristic and a decrease in the measured barrier height with decreasing temperature), as well as the relationship between different barrier heights characterizing a contact, namely, among the actual barrier height, which is measured from a saturation current, the flat-band barrier height, and the barrier height measured from a C — V characteristic.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 769–783, September, 2004.     

宽温变环境的空间反射镜结构分析与研究

相机在从地面到太空的过程中,需要经历重力、温度、气压、辐射等多种环境因素的变化,而这些因素都可能导致空间相机分辨率下降、像质变坏、功能失效甚至系统破坏。所描述的系统工作于18±15℃的温度环境,要求光学反射镜在30℃温度变化范围内仍能正常成像。经优化设计,应用计算机仿真手段进行了静、动态及热特性的分析,提出了一种采用中心粘接结合Bipod柔性支撑形式,解决了在大跨度环境温度范围下的反射镜结构支撑问题。