部分相干双曲余弦厄米高斯光束在非Kolmogorov大气湍流中的传输特性

基于广义Huygens-Fresnel原理和非Kolmogorov大气湍流折射率起伏谱密度函数, 采用Wigner分布函数的二阶矩方法, 推导出了在大气湍流中传输的部分相干双曲余弦厄米高斯光束束宽和M²因子的解析表达式. 研究表明: 相对束宽和归一化M²因子随传输距离的增大而增大; 光束阶数越大、相干长度越小、双曲余弦参数越小, 相对束宽和归一化M²因子受大气湍流影响越小; 相对束宽随束腰宽度的增大存在极大值, 在一定的相干长度范围内, 归一化M²因子随束腰宽度的增大存在极小值; 相对束宽和归一化M²因子随广义指数的变化均存在极大值, 随内尺度的增大而逐渐减小, 随外尺度的增大几乎没有变化.     

Paraxial propagation of partially coherent flat-topped beam

The propagation of flat-topped beam passing through a paraxial optical ABCD system is extended to partially coherent case and has been studied in detail. Based on Wigner distribution function (WDF), the irradiance distribution of partially coherent flat-topped beam is derived. Furthermore, two propagation parameters, such as M²-factor and Power in Bucket (PIB) are illustrated analytically and numerically.     

Watt-level,green-pumped optical parametric oscillator based on periodically poled potassium titanyl phosphate with high extraction efficiency

We report a compact, efficient optical parametric oscillator (OPO) based on a periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by a 532 nm laser, which generated 1.51 W of average power at the signal wavelength of 709 nm with the pulse duration of ～ 1.0 ns. The extraction efficiency was up to 59%. To the best of our knowledge, this is the first report on Watt-level green-pumped PPKTP-based singly resonant oscillator OPO (SRO-OPO). The precise build-up time of OPO was determined to be 1.6 ns benefitting from the characteristic of twin-peak pulse profile of pump beam. The spectrum width of the idler was also measured to be 4.2 nm with the central wavelength of 2134 nm at 0.2 nm spectral resolution of optical spectrum analyzer. In addition, the beam quality of M² < 1.9 of generated signal exhibits a good consistency with M² < 1.5 for the pump source.     

Er~(3+),Yb~(3+):glass-Co~(2+):MgAl_2O_4 diffusion bonded passively Q-switched laser

A Co~(2+):spinel passively Q-switched erbium-ytterbium-phosphate glass bonded laser pumped at 940 nm is reported.A pulse energy of 210 μJ, a peak power over 70 kW, and beam quality M~2 parameter of 1.2 are obtained under a pump power of 235 mW. An unbonded laser output experiment with the same dimension of the active material and the saturable absorber as the bonded laser output experiment is carried out. The reason why the output in the bonded laser is improved is determined.     

Beam quality of a high-power CO2 laser MOPA system

In this paper, the effects of amplification of diffraction-limited pulsed CO₂ laser radiation over several meters of amplification length on beam quality and pointing stability are documented. Millijoule pulses are amplified up to 3 J. Generation and amplification of the 10 μm wavelength pulses were performed in the discharge volume of an e-beam sustained CO₂ laser. Beam quality is measured according to the ISO/DIS 11146 standard in terms of the beam quality factor M². Fluence distributions were recorded with a beam analysing system of 100 μm spatial resolution. M² parameter values ranged up to 1.55 for amplified pulse energies of 3 J. The necessity of beam-quality restoring techniques is inferred for the multijoule pulse energy regime.     

射频离子源束流特性分析

介绍了为HL-2A 装置设计的引出束功率为1MW 的射频离子源研制情况。目前,在测试平台上,该离子源已经成功引出了束能量和束电流分别为35keV 和12.4A、束质子比为79%、脉宽为100ms 的氢离子束,达到了其设计束功率的44%。用红外热成像的方法测量了离子束能量密度分布。结果表明,在距离引出系统地电极 1.3m 处,束密度分布遵循高斯分布。引出束的最佳导流系数为1.689×10^–6A•V^-3/2 左右,随射频功率改变有较小的变化。根据这些实验结果,采取了相关改进措施来改善离子源的引出束性能。     

Propagation and coherence properties of higher order partially coherent dark hollow beams in turbulence

We formulate and evaluate in terms of graphical outputs, source and receiver plane expressions, the complex degree of coherence, beam size variation and power in bucket performance for higher order partially coherent dark hollow beams propagating in turbulent atmosphere. Our formulation is able to cover square, rectangular, circular, elliptical geometries for dark hollow and flat-topped beams in one single expression. From the graphical outputs of the receiver plane, it is observed that higher order partially coherent dark hollow beams will initially develop an outer ring around a central lobe, but will eventually evolve towards a Gaussian shape as the propagation distance is extended. It is further observed that stronger turbulence levels and greater partial coherence have similar effects on beam profile. During propagation, modulus of complex degree of coherence of partially coherent dark hollow beams appears to rise above that of the source plane values, reaching as high as near unity. Beam size analysis shows that, among the types examined, (nearly) flat-topped beam experiences the least beam expansion. Power in bucket analysis indicates that lowest order square fully coherent dark beam offers the best power capturing.     

Testing supersymmetry in the associated production of CP-odd and charged Higgs bosons

In the Minimal Supersymmetric Standard Model (MSSM), the masses of the charged Higgs boson (H±) and the CP-odd scalar (A) are related by MH+2=MA2+mW2. Furthermore, because the coupling of W−–A–H+ is fixed by gauge interaction, the tree level production rate of depends only on one supersymmetry parameter—the mass (MA) of A. We show that to a good approximation this conclusion also holds at the one-loop level. Consequently, this process can be used to distinguish MSSM from its alternatives (such as a general two-Higgs-doublet model) by verifying the above mass relation, and to test the prediction of the MSSM on the product of the decay branching ratios of A and H± in terms of only one single parameter—MA.     

Optical fibre beam delivery of high-energy laser pulses: beam quality preservation and fibre end-preparation

This paper investigates the extension of optical fibre beam delivery to high-brightness applications, in particular laser percussion drilling, where both a good beam quality and high peak power are required. Beam quality preservation through a number of optical fibres is studied both experimentally and by using a ray propagation model. It is determined that in order to achieve the beam quality required for percussion drilling (M²<30) the largest fibre which can be used is 400 μm diameter. The laser-induced damage threshold is measured for a number of 400 μm fibres, and a CO₂ laser-annealing technique is shown to increase the damage threshold by a factor of 10, allowing 28 J, 1 ms pulses to be transmitted.     

Axial superposition of Gaussian spherical beams

A novel model of beam formed by coherent superposition of two correlated Gaussian spherical beams with different centers is presented. This kind of beam has a transverse spreading smaller than a fundamental Gaussian beam. The beam quality factor is smaller than one.     

Field-induced parameters of re-entrant magnets and concentrated spin glasses

We have used electron spin resonance measurements to derive the temperature and frequency dependences of the field-induced magnetization [M(T, f)] and anisotropy field [H_an (T)] in a number of amorphous alloys belonging to the series (Fe_pNi_1−p)₇₅P₁₆B₆Al₃. In re-entrant (p > p_c, the critical concentration for ferromagnetism) alloys at hi gh frequencies (f = 35 GHz, field ≈ 12 kOe) M reduces as T^3/2 at high T and as T below ≈ 40 K, the deviation from T^3/2 becoming more marked as p → p⁺_c. For p close to p_c, lowering the frequency first causes the T term to increase and ultimately ( ≈ 4 GHz) changes the variation of M with T to that discovered previously for concentrated spin glasses, namely M is constant at low T and drops linearly at high temperatures. For the re-entrants, the results are interpreted on the basis of a model which invokes an energy gap in the spin-wave spectrum, introduces a non-zero density of states of the gap energy and takes into consideration a low-q cut-off in the spin-wave integral in thelow-T (T) regime.In the concentrated spin glasses [M (0) - M (T)]/ M (0) is well represented by the function [exp (Δ / T) - 1]^-1, where Δ has values close to the corresponding Curie-Weiss temperatures θ_p but much larger than the respective spin glass transition temperatures T_SG. The temperature dependence of H_an is largely given by the function (1 - T/T^*), where T^* is equal to the zero-field freezing temperature for the re-entrants and T_SG for the spin glasses, respectively.     

100-W class diode-pumped Nd:YAG MOPA system with a double-stage relay-optics scheme

We describe a diode-pumped master-oscillator power-amplifier system with two-rod Nd:YAG media and double-stage relay optics scheme. At the repetition rate of 2.4 kHz it delivers an average power of 108 W with Q-switched pulses of 47 ns duration. The laser beam is characterized by an M² factor of 2.5×2.7. A model of amplification, which takes into account the temporal overlap between the beams that propagate forwards and backwards in the amplifier stage, was developed to explain the experimental results.     

铕掺杂类水滑石的发光性质及其选择性红外吸收

采用共沉淀法水热合成了稀土Eu掺杂的镁铝类水滑石层状化合物(MgAlEuCO₃-HTlcs)。探讨了溶液pH值、组分配比、陈化时间和温度对水滑石晶体结构的影响。利用XRD、FT-IR和荧光光谱对样品的组成和性质进行表征。XRD、FT-IR结果表明:当n(M²⁺):n(M³⁺)=3,n(Eu³⁺):[n(Al³⁺)+n(Eu³⁺)]=5%~50%,pH=10±0.1条件下进行多种离子共沉淀,并经100℃、12h水热处理后均可得到结晶好、纯度高的镁铝铕类水滑石;MgAlEuCO₃-HTlcs保持了水滑石的层状结构,在600~900cm^-1、1250~1350cm^-1和3420~3480cm^-1有红外吸收;荧光光谱测试发现掺杂稀土Eu³⁺离子的MgAlEuCO₃-HTlcs具有Eu³⁺的⁵D₀→⁷F_J特征光谱。稀土Eu³⁺成功地插层组装进入HTlcs层板,MgAlEuCO₃-HTlcs化合物是一种具有选择性红外吸收和红色发光性质的双功能材料。     

Quantum superreplication of states and gates

Although the no-cloning theorem forbids perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superreplication, can occur for both quantum states and quantum gates. The aim of this paper is to review the central features of quantum superreplication and provide a unified view of existing results. The paper also includes new results. In particular, we show that when quantum superreplication can be achieved, it can be achieved through estimation up to an error of size O(M/N²), where N and M are the number of input and output copies, respectively. Quantum strategies still offer an advantage for superreplication in that they allow for exponentially faster reduction of the error. Using the relation with estimation, we provide i) an alternative proof of the optimality of Heisenberg scaling in quantum metrology, ii) a strategy for estimating arbitrary unitary gates with a mean square error scaling as log N/N², and iii) a protocol that generates O(N²) nearly perfect copies of a generic pure state U|0>while using the corresponding gate U only N times. Finally, we point out that superreplication can be achieved using interactions among k systems, provided that k is large compared to M²/N².     

A 515-nm laser-pumped idler-resonant femtosecond BiB3O6 optical parametric oscillator

We report on an idler-resonant femtosecond optical parametrical oscillator(OPO)based on BiB₃O₆(BiBO)crystal,synchronously pumped by a frequency-doubled,mode-locked Yb:KGW laser at 515 nm.The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm.At a repetition rate of 75.5 MHz,the OPO generates as much as 400 mW of idler power with 3.1 W of pump power,the corresponding pulse duration is 80 fs,which is 1.04 times of Fourier transform-limited(FTL)pulse duration at 1305 nm.In addition,the OPO exhibits excellent beam quality with M²<1.8 at 1150 nm.To the best of our knowledge,this is the first idler-resonant femtosecond OPO pumped by 515 nm.     

New expressions for field distribution in the focal region

In an earlier paper dealing with the flat-topped light beams [Y. Li, Opt. Lett. 27 (2002) 1007], it is shown that the flat-topped beams can be expressed as 1 − [1 − exp(−ξ²)]^M, where ξ is a dimensionless parameter and M is a non-negative number. The binomial expansion of this express contains only lowest-order Gaussian modes; this situation makes it possible to develop a new formulation of diffraction of converging spherical wave at an aperture in a plane opaque screen if the Gaussian mode expansion is employed to describe the boundary values of the screen.     

Transformation of optical-vortex beams by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by the “fork” holograms from incident circular Laguerre-Gaussian modes are studied theoretically. The complex amplitude distribution of a diffracted beam is described by models of the Kummer beam or of the hypergeometric-Gaussian beam. Physically, in most cases its structure is formed under the influence of the divergent spherical wave originating from the discontinuity caused by the hologram’s groove bifurcation. Presence of this wave is manifested by the ripple structure in the near-field beam pattern and by the power-law amplitude decay at the beam periphery. Conditions when the divergent wave is not excited are discussed.The diffracted beam carries a screw wavefront dislocation (optical vortex) whose order equals to algebraic sum of the incident beam azimuthal index and the topological charge of the singularity imparted by the hologram. The input beam singularity can be healed when the above sum is zero. In such cases the diffracted beam can provide better energy concentration in the central intensity peak than the Gaussian beam whose initial distribution coincides with the Gaussian envelope of the incident beam. Applications are possible for generation of optical-vortex beams with prescribed properties and for analyzing the optical-vortex beams in problems of information processing.     

The ΔNγ electromagnetic transition form factors GM(q) and GE(q)

A parameter-free, nonperturbative calculation of the ΔNγ electromagnetic transition amplitudes GM*(q2), GE*(q2), and the resonant multipole ratio REM(q2)≡E1+3/2(q2)/M1+3/2(q2) is performed in terms of the well-known nucleon isovector Sachs form factor GMV. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that GM*(q2) decreases more rapidly than the nucleon dipole form factor when −q21 GeV2/c2 and that REM(q2) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction REM(q2)→1 is purely asymptotic and is valid only for extremely high |q2|.     

Nd:YAG薄片激光器热致波前畸变

 理论分析了激光二极管端面泵浦薄片Nd:YAG 激光器的激光介质热效应对波前相位分布的影响，给出了薄片激光器波前热畸变的计算公式。数值模拟了理想均匀泵浦及4阶超高斯泵浦下的波前分布，分析了介质厚度和泵浦均匀性与波前畸变量的关系。研究表明，介质越薄，激光泵浦光均匀性越好，泵浦功率密度越小，激光波前畸变越小；与介质厚度、泵浦功率密度相比，泵浦光光强分布对波前的影响更为显著。     

Measurement of the slope parameter for the neutral pion spectrum in KL → πππ decay

The π⁰ spectrum in the K_L⁰ → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M² ≈ 1 + 2a₀(M_K/M_π²)(2T_π⁰−T_π⁰max) + a₁(M_K²/M_π⁴)(2T_π⁰−T_π⁰max)². We obtained a₀ = −0.282 ± 0.011 and a₁ consistent with zero.