金激光等离子体的空间分辨X射线发射谱及其应用

在星光II激光装置上,采用PET平面晶体谱仪与宽20μm的狭缝构成一维空间分辨光谱测量系统,对金平面靶激光等离子体进行观测,获得了沿靶面法向一维空间分辨的金M带发射谱。在实验谱中观察到了Au元素类Ni离子的电四极跃迁线3p63d10(1S0) 3p53d104d(3/2,5/2)J=1。利用电四极跃迁线对电子密度的敏感特性,开展了金激光等离子体电子密度诊断的尝试,确定出利用该谱线进行电子密度诊断的有效范围大致在1019～4.5×1021cm-3之间。     

Circular polarization of the (1s2p)2 → (1s2)0 line emitted by 205Tl79+ ions after collisional excitation by an unpolarized electron beam

The circular polarization of the (1s2p)_J=2 → (1s²)_J=0 line emitted by the helium-like ion ²⁰⁵Tl⁷⁹⁺ following impact excitation by a nonpolarized electron beam is theoretically studied. The probability for the hyperfine induced E1 transition (1s2p)₂F=3/2→1s² has been determined from the first order perturbation theory. Various collision strengths for excitation of thallium ions to the (1s2p)₂M_J=0, 1 and 2 magnetic sublevels have been used. It is found that the interference between M2 and E1 radiation occurring in the line can give rise to a significant degree of circular polarization. This revised version was published online in August 2006 with corrections to the Cover Date.     

用类氦双电子复合伴线诊断Ar等离子体电子温度

在电子密度约为ne=10 13 cm-3 条件下计算了类氦Ar的伴线 j(1s2 2 p2 P3 / 2 - 1s2 p2 2 D5/ 2 )与共振线w(1s2 1S0 - 1s2P1P1)的强度比 ,采用Hartree Fork Relativistic (HFR)方法计算了伴线因子和波长 ,从而得到伴线强度以及强度比。根据计算的相对强度比随温度的变化关系可以利用实验诊断电子温度     

Dynamic transition and hysteresis scaling in Heisenberg ferromagnet

Based on the mean-field treatment and Monte Carlo simulation, we studied the nature of the dynamic phase transition of two and three-dimensional magnetic films in Heisenberg model. The time averaged magnetization components ( mx , my, mz),the average hysteresis-loop area components A for magnetic films with different thickness have been calculated. The dynamic transition phase diagrams from to Q=0 for the 2D and 3D cases have been obtained. The relaxation times for different values of magnetic field, temperature, thickness of the films and the orientation number of spin have been simulated. It is found that the loop area follows the scaling relation, A-A0H0 T-, and the exponents and increase with increasing thickness, while the exponent decreases with increasing thickness. It was observed that the phase boundary line shrinks inward in the H0-T plane with decreasing value of the frequency of the magnetic field and thickness of multilayer film. The phase diagrams were explained by the competition between the relaxation time and the period of the external magnetic field. Moreover, it has been indicated that the dynamical behaviors for 2D and 3D cases derived by both mean-field method and Monte Carlo method in this work are consistent.     

Most electron heat transport is not anomalous; it is a paleoclassical process in toroidal plasmas

It is hypothesized that radial electron heat transport in magnetically confined toroidal plasmas results from paleoclassical Coulomb collision processes (parallel electron heat conduction and magnetic field diffusion). In such plasmas the electron temperature is equilibrated along magnetic field lines a long length L (> poloidal periodicity length piR0q), which is the minimum of the electron collision length and an effective field line length. Thus, diffusing field lines induce a radial electron heat diffusivity M identical with L/(piR0q) approximately 10>1 times the magnetic field diffusivity eta/mu0 approximately nue(c/omegap)2.     

Evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence

We study the evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence. By quasilinearizing the Navier-Stokes equation, we solve analytically the induction equation in the quasinormal approximation. We find that, if the magnetic field is not helical, the magnetic energy and correlation length evolve in time, respectively, as E(B) proportional to t(-2(1+p)/(3+p)) and xi(B) proportional to t(2/(3+p)), where p is the index of initial power-law spectrum. In the helical case, the magnetic helicity is an almost conserved quantity and forces the magnetic energy and correlation length to scale as E(B) proportional to (logt)(1/3)t(-2/3) and xi(B) proportional to (logt)(-1/3)t(2/3).     

不同磁场环境下Heisenberg XXZ自旋链中的热量子失协

本文研究了不同磁场环境下一维Heisenberg XXZ自旋链中两量子比特的热量子失协特性. 在四种不同的磁场环境下: 1) B₁=B₂=0 (无磁场); 2) B₁≠0, B₂=0 (磁场只作用于其中一个量子比特); 3) B₁=B₂ (均匀磁场); 4) B₁=-B₂ (非均匀磁场), 对分别作用在每个量子比特上的磁场B₁和B₂对其量子关联的影响作了详细的讨论, 且数值计算和比较了其量子失协和量子纠缠的异同. 结果显示: 在有限温度下, 量子失协相比于量子纠缠更普遍, 且非均匀磁场相比于均匀磁场对量子失协和量子纠缠更有用, 更有利于量子通讯和量子信息处理过程. 关键词： 量子关联 纠缠 量子失协     

The Rippled-Field Magnetron (Cross-Field Free Electron Laser)

Millimeter-wave emission from the rippled-field magnetron (cross-field free electron laser (FEL)) is investigated experimentally and theoretically. In this device, electrons move in quasi-circular orbits under the combined action of a radial electric field, a uniform axial magnetic field, and a radial azimuthally periodic wiggler magnetic field. In excess of 300 kW of RF power is observed in two narrow spectral lines whose frequency can be tuned continuously from ~25 to ~50 GHz by variation of the axial magnetic field. The observations are interpreted as a FEL type of instability, associated with a resonance in the particle motion of a layer of electrons embedded in the dense spacecharge cloud. The resonance is shown to occur when 2kw?0 ? (?>0/?0) ?1 -(?p/?0)2, where kw is the wiggler wavenumber, ?0 is the azimuthal electron velocity, ?0 is the relativistic cyclotron frequency in the axial magnetic field, wp is the relativistic plasma frequency, and ?0 = [1 - (?0/c)2]-1/2 of the resonant electron layer.     

Magnetic quantum oscillations in nanowires

Analytical expressions for the magnetization and the longitudinal conductivity of nanowires are derived in a magnetic field, B. We show that the interplay between size and magnetic field energy-level quantizations manifests itself through novel magnetic quantum oscillations in metallic nanowires. There are three characteristic frequencies of de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillations, F = F(0)/(1 + gamma)(3/2), and F(+/-) = 2F(0)/|1 + gamma +/- (1 + gamma)(1/2)|, in contrast with a single frequency F(0) = S(F)plankc/(2pie) in simple bulk metals. The amplitude of oscillations is strongly enhanced in some magic magnetic fields. The wire cross-section area S can be measured using the oscillations as S = 4pi(2)S(F)plank(2)c(2)/(gammae(2)B(2)) along with the Fermi-surface cross-section area, S(F).     

PrNi$lt;sub$gt;2$lt;/sub$gt;的磁和磁热性能研究

在一些磁性材料内, 磁性离子间交换作用和磁性离子的自旋涨落对材料磁性有影响. 本文根据磁比热实验值确定了晶场参数后, 利用包含自旋涨落的交换作用有效场H_m= n₀ (1 + γ T + β e^{ω T})M, 计算了PrNi₂晶体晶场能级的Zeeman劈裂. 在温度为3.8 K ≤T≤ 30 K范围内, 计算了该晶体多晶磁矩随外磁场的变化, 以及外磁场H=5000 Oe时磁化率倒数随温度的变化, 计算结果和实验值符合较好. 当外磁场在0–50000 Oe时, 计算的该晶体的磁熵变与已有文献的理论结果相似. 计算结果说明, 提出的包含自旋涨落的交换作用有效场不仅适合亚铁磁性晶体, 而且也适合顺磁性晶体. 关键词： 2')" href="#">PrNi₂ 磁比热 交换作用有效场 磁矩 磁熵变     

圆偏振飞秒激光脉冲与低压氙气体靶相互作用软X射线辐射实验研究

利用平场光栅谱仪,分别在2和3 kPa的低气压下,测量了脉宽35 fs的圆偏振超强超短激光脉冲与5 mm长氙气体靶相互作用产生的波长在5～60 nm范围内的离子谱线。2 kPa时最强的跃迁为XeⅧ：4d105s(2S_1/2)—4d95s5p(2P_3/2)的17.085 6 nm线,3 kPa时最强的跃迁为11.343 nm的XeⅦ 4d105s2(1S0)—4d95s25f(3P₁)跃迁。两种气压下,Xe均被电离到XeⅦ,XeⅧ,XeⅨ态。     

光谱的精密仿真技术及NO的高分辨LMR谱的仿真研究

LMR(Laser Magnetic Resonance)光谱技术采用磁场扫描及磁场调制获得顺磁分子吸收谱线,其谱线具有Voigt线型及各不相同的磁场线宽.本文考虑线型理论模型和实验条件,提出了一种实现LMR谱精密仿真的方法,并设计了相应仿真计算程序.对¹⁵N¹⁶O的X²Π_3/2v=1←0,Q₂(2.5)在激光频率为1842.8160cm^-1处的塞曼跃迁谱进行了仿真,得到了理想的仿真效果.该方法可作为复杂光谱分析标识的有效辅助工具.     

Topology of toroidal helical fields in non-circular cross-sectional tokamaks

The ordinary differential magnetic field line equations are solved numerically; the tokamak magnetic structure is studied on Hefei Tokamak-7 Upgrade （HT-TU） when the equilibrium field with a monotonic q-profile is perturbed by a helical magnetic field. We find that a single mode （m, n） helical perturbation can cause the formation of islands on rational surfaces with q=m/n and q=（m±1,±2,±3,...）/n due to the toroidicity and plasma shape （i.e. elongation and triangularity）, while there are many undestroyed magnetic surfaces called Kolmogorov-Arnold-Moser （KAM） barriers on irrational surfaces. The islands on the same rational surface do not have the same size. When the ratio between the perturbing magnetic field Br（r） and the toroidal magnetic field amplitude Bφ0 is large enough, the magnetic island chains on different rational surfaces will overlap and chaotic orbits appear in the overlapping area, and the magnetic field becomes stochastic. It is remarkable that the stochastic layer appears first in the plasma edge region.     

锶原子光晶格钟自旋极化谱线的探测

87Sr原子存在核自旋,在磁场作用下原子能级会分裂成不同塞曼子能级.通过光抽运对原子进行自旋极化,其自旋极化谱线的探测为锶光钟系统的闭环锁定提供精确的频率参考.本文对~(87)Sr原子钟跃迁能级5s~2~1S_0→5s5p~3P_0中的m_F=+9/2和m_F=-9/2的塞曼磁子能级自旋极化谱线进行了探测.经过一级宽带冷却和二级窄线宽冷却与俘获后,锶冷原子温度为3.9μK,原子数目为3.5×10~6.利用邻近"魔术波长"的813.426 nm半导体激光光源实现水平方向的一维光晶格装载.采用归一化探测方法用线宽为Hz量级的698 nm钟激光对~1S_0→~3P_0偶极禁戒跃迁进行探测,在150 ms的探测时间下获得线宽为6.7 Hz的钟跃迁简并谱.在磁光阱竖直方向施加一个300 mGs的偏置磁场获得塞曼分裂谱,并通过689 nm的圆偏振自旋极化光进行光抽运,最终在探测时间为150 ms时,获得左右旋极化谱线线宽分别为6.2 Hz和6.8 Hz.     

Line shape and lifetime in argon 2p electron spectroscopy

The argon 2p photoelectron spectrum and the argon L₃M₂₃M₂₃ ¹S₀ Auger spectrum have been measured at several photon energies between 6 and 80 eV above the 2p_3/2 threshold with an instrumental line width significantly smaller then the natural line width. The spectra are described well by the theory of van der Straten et al. [Z. Phys. D 8 (1988) 35] provided that allowance is made for the instrumental resolution and measurements are made at a sufficiently low pressure. The lifetime (Lorentzian) line width determined from these measurements for the core-ionized atom is 112±3 meV, in good agreement with the line width for the 2p_3/2→4s core-excited state, 114±2 meV, indicating that the 4s electron has little influence on the Auger decay rate. Remeasurement of the line width for the carbon 1s hole in carbon dioxide gives values in good agreement with the previous measurement of 99 meV.     

Application of the photon's intrinsic flux to the 1s‐2p and 2p‐3d excitonic transitions in nanostructures

We have applied our two recent results [depending on its helicity photon carries a quantum flux of ± Φ ₀ = ± hc/e and the quantized magnetic fluxes through the electronic orbits of the Dirac hydrogen atom are given by: Φ (n,l,m_j) = (n‐l‐m_j)Φ₀) ] to the 1s‐2p and 2p‐3d excitonic transitions in nanostructures. It is shown that the flux changes for the non‐zero matrix elements in the 1s‐2p and 2p‐3d excitonic transitions is either ± Φ₀ or zero. The present result supports the previous results stated above. It is also shown that spin flip is possible in the 1s‐2p and 2p‐3d excitonic transitions.     

Magnetization and magnetic phase diagrams of a spin-1/2 ferrimagnetic diamond chain at low temperature

We used the Jordan–Wigner transform and the invariant eigenoperator method to study the magnetic phase diagram and the magnetization curve of the spin-1/2 alternating ferrimagnetic diamond chain in an external magnetic field at finite temperature. The magnetization versus external magnetic field curve exhibits a 1/3 magnetization plateau at absolute zero and finite temperatures, and the width of the 1/3 magnetization plateau was modulated by tuning the temperature and the exchange interactions. Three critical magnetic field intensities H_(CB), H_(CE) and H_(CS) were obtained, in which the H_(CB) and H_(CE) correspond to the appearance and disappearance of the 1/3 magnetization plateau, respectively, and the higher H_(CS) correspond to the appearance of fully polarized magnetization plateau of the system. The energies of elementary excitation ωσ,k(σ = 1, 2, 3) present the extrema of zero at the three critical magnetic fields at 0 K, i.e., [hω_(3,k)(HCB)]_(min)= 0, [hω_(2,k)(H_(CE))]_(max)= 0 and [hω _(2,k)(H_(CS))]_(min)= 0, and the magnetic phase diagram of magnetic field versus different exchange interactions at 0 K was established by the above relationships. According to the relationships between the system's magnetization curve at finite temperatures and the critical magnetic field intensities, the magnetic field-temperature phase diagram was drawn. It was observed that if the magnetic phase diagram shows a three-phase critical point, which is intersected by the ferrimagnetic phase, the ferrimagnetic plateau phase, and the Luttinger liquid phase, the disappearance of the1/3 magnetization plateau would inevitably occur. However, the 1/3 magnetization plateau would not disappear without the three-phase critical point. The appearance of the 1/3 magnetization plateau in the low temperature region is the macroscopic manifestations of quantum effect.     

Optical decoherence times and spectral diffusion in an Er-doped optical fiber measured by two-pulse echoes, stimulated photon echoes, and spectral hole burning

Two-pulse and stimulated photon echoes and spectral hole burning were measured on the transition from the lowest component of the ⁴I_15/2 manifold to the lowest component of ⁴I_13/2 of Er³⁺ in a silicate optical fiber at 1.6 K. The two-pulse echo decays gave decoherence times as long as 230 ns for magnetic fields above 2 T. A large field dependent contribution to the homogeneous line width of >2 MHz was found and interpreted in terms of coupling to magnetic tunneling modes (TLS) in the glass. The stimulated echoes measured at 2 T showed spectral diffusion of 0.8 MHz/decade of time between 0.4 and 500 μs. Spectral diffusion in this high field region is attributed to coupling to elastic TLS modes which have a distribution of flip rates in glasses. Time-resolved spectral hole burning at very low field showed stronger spectral diffusion of 5.7 MHz/decade of time, attributed to coupling to magnetic spin-elastic TLS modes.     

Magnetized cosmological model

The object of this paper is to investigate the behavior of the magnetic field in a cosmological model for perfect fluid distribution. The magnetic field is due to an electric current produced along thex axis. It is assumed that expansion () in the model is proportional to ₁ ¹ , the eigenvalue of the shear tensor _i ^j . The behavior of the model when the magnetic field tends to zero and other physical properties are also discussed.     

Hall conductivity for two-dimensional magnetic systems

A Kubo inspired formalism is proposed to compute the longitudinal and transverse dynamical conductivities of an electron in a plane (or a gas of electrons at zero temperature) coupled to the potential vector of an external local magnetic field, with the additional coupling of the spin degree of freedom of the electron to the local magnetic field (Pauli Hamiltonian). As an example, the homogeneous magnetic field Ha]] conductivity is rederived. The case of the vortex at the origin is worked out in detail. This system happens to display a transverse Ha]] conductivity (P breaking effect) which is subleading in volume compared to the homogeneous field case, but diverging at small frequencies like 1/ω². A perturbative analysis is proposed for the conductivity in the random magnetic impurity problem (Poissonian vortices in the plane). At first order in perturbation theory, the Ha]] conductivity displays oscillations close to the classical straight line conductivity of the mean magnetic field.