邻碘甲苯分子光解动力学的飞秒时间分辨质谱研究

利用飞秒时间分辨质谱技术研究了邻碘甲苯分子在266 nm激发下的光解动力学. 光解产物碎片通过800 nm强激光场下的多光子电离实现探测. 拟合光解产物C₇H₇自由基和I原子随泵浦-探测延迟时间变化的信号,得到解离时间为38±50 fs,它反映的是266 nm同时激发nσ^*和ππ^*态后C-I键的平均解离时间. 此外,还利用基态碘原子的共振波长298.23 nm作为探测光,通过共振增强多光子电离方法对解离生成的基态碘原子进行了选择性探测. 拟合I⁺随泵浦-探测延迟时间变化的信号,得到解离时间为40±50 fs,这与通过800 nm多光子电离得到的解离时间一致,表明解离生成的主要产物是基态碘原子.     

量子限制受主远红外电致发光器件的制备与测量

采用分子束外延技术生长GaAs/AlAs三量子阱,并在中间的GaAs阱中δ-掺杂浅受主杂质Be原子,制作出量子限制受主远红外Teraherz原型电致发光器件.实验上测量得到4.5 K时器件的电致发光谱（EL）和电传输特性（I-V曲线）.在EL发射谱中清楚地观察到222 cm^-1处宽的尖峰,这来源于Be受主奇宇称激发态到其基态的辐射跃迁,而非辐射弛豫过程则使发射谱的信号很弱.另外在I-V曲线中072和186 V的位置出现两个共振隧道贯穿现象,分别对应于中间δ-掺杂量子阱受主能级1s_3/2(Γ₆+Γ₇)到左边非掺GaAs量子阱中HH带,及右边非掺杂GaAs量子阱中HH重空穴带到中间掺杂GaAs量子阱中Be受主杂质原子奇宇称激发态2p_5/2(Γ₆+Γ₇)能级的共振隧穿.     

高能正负电子对的湮没与超窄共振ψ粒子的作用

本文给出了R=(σ(e⁺e^-→强子))/(σ(e⁺e^-→μ⁺μ^-))随能量上涨的一个解释。研究了新发现ψ粒子所具有作用的性质,指出其强度f²/(4π)～10^-5—10^-6。求得峰值截面σ₀=(12π)/m_ψ²(Γ(ψ→e⁺e     

小变形原子核中的相干效应

本文考察了在转动的小变形核力场中运动的核子-核子对、核子-空穴对中的相干效应。计算了O¹⁸最低的偶宇称态0⁺,2⁺,4⁺和O¹⁶最低的奇宇称态0^-,1^-,2^-,3^-波函数;和壳模型经典方法计算出的结果作了比较,二者相当一致。得出的初步结论如下:核力主要是P₂力再加上一定成分具有相干性质的力。前者与转动的变形场等效。不但对于0⁺,2⁺,4⁺,3^-态,而且对于1^-,2^-态,附加的相干成分都很重要;它们的内部态混合组态是比较多的,粒子-粒子之间、或粒子-空穴之间的关联都比较显著。只有0^-态的内部态是纯组态。     

激发对相干态的等阶Y压缩效应

用数值计算法研究了激发对相干态|ζ;m〉＝a^+mb^+m|ζ〉的等阶Y压缩效应.结果表明:对于态a^+mb^+m|ζ〉,光场存在着等阶K(＝2,3,4,5,…)次方Y压缩效应,但是随着场模上光子增加数m的增大,等阶K次方Y压缩效应减弱.     

Registration of hydrogen-like leptonic bound states ( e-μ+) and ( e+μ-) in reactions of high-energy scattering of polarized electrons and positrons by nuclei with Z ～ 100 and analysis of CPT invariance

The cross-sections for the reactions of muonium (anti-muonium) production in the high-energy electron (positron) scattering by nuclei e ^-(e ⁺) + Z↦Z + M ⁰(ˉM) + μ^-(μ⁺) are calculated in dependence on energy and polarization of the initial electron (positron) and polarization of the final μ^-(μ⁺)-meson. Since this is a coherent phenomenon the cross-sections are proportional to Z². For Z ∼ 100, due to the factor Z², the cross-sections are large enough to be measured at the energies available for the HERA Collider at DESY. The results are discussed in connection with a test of CPT invariance. Received: 24 September 2002 / Accepted: 12 March 2003 / Published online: 27 May 2003     

利用激光溅射原子束装置结合时间切片速度成像技术对于金属态-态反应动力学的相关研究

利用新建激光溅射交叉分子束装置,结合时间切片速度成像技术开展了金属原子态-态反应动力学的相关研究. 超声金属原子束是由激光溅射金属棒产生,结合无气体溢流通道的自由扩散设计,得到了质量很好的金属原子超声束. 本文选择Al+O₂反应体系来测试新建金属交叉分子束实验装置的性能. 通过(1+1) 共振多光子电离技术,以AlO(D²∑⁺)为中间态来探测特定转动态的产物AlO自由基. 相同波长下可以同时得到反应产物AlO(X²∑⁺,v=0,N和N+14)两个转动态的速度成像,分别对应着Δv=1的P(N)和R(N+14)跃迁. 在244.145 nm同时探测到P(15)和R(29)的跃迁,形成的两个环在切片成像图中可以完全区分开,这两个跃迁分别对应着反应产物AlO(v=0,N=15)和AlO(v=0,N=29)两个转动态. 对应此两个转动态的能级差为403 cm^-1. 这两个反应产物转动态的区分表明了该实验装置与最近的一篇研究报道[J. Chem. Phys. 140, 214304 (2014)]相比较,具有较好的碰撞能量分辨率.     

高电荷态离子入射Al表面库仑势对靶原子特征谱线强度的影响

用同一动能(150keV)而不同电荷态的⁴⁰Ar^q+(8≤q≤16)离子入射金属Al表面，靶原子受激辐射产生特征光谱线. 实验结果表明：高电荷态离子与金属表面相互作用过程中，经过与靶原子碰撞(Penning碰撞)交换动能和共振电子俘获(resonant capture)释放库仑势能，将携带的能量沉积于靶表面，使靶原子激发. 这种激发不同于光激发，它不仅激发了原子复杂电子组态之间的跃迁，而且跃迁辐射的特征谱线强度增强的趋势与入射粒子的库     

增加光子奇偶q相干态的高阶压缩效应

通过数值计算研究了增加光子奇q相干态a_q^+m|α>_q^o和增加光子偶q相干态a_q^+m|α>_q^e的高阶压缩效应.结果表明:当q较小时,态a_q^+m|α>_q^o和a_q^+m|α>_q^e都能呈现出强烈的奇次方阶压缩效应,但无偶次方阶压缩效应,而且奇次方阶压缩随m的增大而增强.当m=0时a_q^+m|α>_q^o和a_q^+m|α>_q^e为光场振幅偶次幂的最小测不准态,但当m≠0时它们不是光场振幅偶次幂的最小测不准态.     

Meson-baryon s-wave resonances with strangeness -3

Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian ( Phys. Rev. D 74, 034025 (2006)), we study the s-wave meson-baryon resonances in the strangeness S = - 3 and negative-parity sectors. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho-meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2⁺ octet of the nucleon and the 3/2⁺ decuplet of the Delta. Quantum numbers I(J ^P) = 0(3/2^-) are suggested for the experimental resonances Ω ^*(2250)^- and Ω ^*(2380)^-. Among other, resonances with I = 1 are found, which minimal quark content is sssˉl', being s the strange quark and l, l' any of the the light up or down quarks. A clear signal for such a pentaquark would be a baryonic resonance with strangeness -3 and electric charge -2 or 0, in proton charge units. We suggest looking for K ^- Ξ ^- resonances with masses around 2100 and 2240MeV in the sector 1(1/2^-), and for π ^± Ω ^- and K ^- Ξ ^*- resonances with masses around 2260MeV in the sector 1(3/2^-).     

High contrast atomic magnetometer based on coherent population trapping

We present an experimental and theoretical investigation of the coherent population trapping （CPT） resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin｜｜lin tran- sition scheme is a promising alternative to the conventional circular-circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.     

On the unique possibility of significantly increasing the contrast of dark resonances on the D1 line of <Superscript>87</Superscript>Rb

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for the D1 line of alkali atoms with nuclear spin I = 3/2 by bichromatic linearly polarized light (lin‖lin field) under the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for the D1 line of ⁸⁷Rb.     

Coherent population trapping magnetometer by differential detecting magneto–optic rotation effect

A pocket coherent population trapping(CPT) atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated.Using the differential detecting magneto–optic rotation effect,a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained.The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order,and the ability to detect weak magnetic fields is extended one-fold.Therefore,the proposed scheme is suited to realize a pocket-size CPT magnetometer.     

Subkilohertz linewidths measured by heterodyne-detected coherent population trapping in sodium vapor

Subkilohertz spectroscopy by coherent population trapping (CPT) has been performed in Na atomic vapor. The system employs a frequency-swept acousto-optic modulator for bichromatic excitation as well as a heterodyne-lock-in detection technique that permits the direct measurement of the CPT dispersion curves at a good signal-to-noise ratio. A CPT linewidth of -400 Hz was measured as well as a steep refractive-index dispersion of as much as 3.3 x 10(-10) Hz(-1), corresponding to a group velocity of 1800 m/s.     

Investigation of the nonlinear CPT spectrum of ~(87)Rb and its application for large dynamic magnetic measurement

The coherent population trapping(CPT) phenomenon has found widespread application in quantum precision measurements. Various designs based on the narrow resonant spectrum corresponding to the linear Zeeman effect have been demonstrated to achieve high performance. In this article, the nonlinear Zeeman split of the CPT spectrum of ~(87)Rb in the lin||lin setup is investigated. We observe re-split phenomenon for both magnetic sensitive and magnetic insensitive CPT resonant lines at a large magnetic field. The re-split in the magnetic sensitive lines raises a practical problem to magnetometers worked in the lin||lin setup while the other one shows a good potential for applications in large magnetic field. We propose a design based on the nonlinear split of the magnetic insensitive lines and test its performance. It provides a much larger measurement range compared to the linear one, offering an option for atomic magnetometers where a large dynamic range is preferred.     

Lineshape asymmetry for joint coherent population trapping and three-photon N resonances

We show that a characteristic two-photon lineshape asymmetry arises in coherent population trapping (CPT) and three-photon (N) resonances, because both resonances are simultaneously induced by modulation sidebands in the interrogating laser light. The N resonance is a three-photon resonance in which a two-photon Raman excitation is combined with a resonant optical pumping field. This joint CPT and N resonance can be the dominant source of lineshape distortion, with direct relevance for the operation of miniaturized atomic frequency standards. We present the results of both an experimental study and theoretical treatment of the asymmetry of the joint CPT and N resonance under conditions typical to the operation of an N resonance clock.     

Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ^85Rb

An atomic clock system based on coherent population trapping （CPT） resonance in 85Rb is reported, while most past works about the CPT clock are in ST Rb. A new modulation method （full-hyperfine-frequency-splitting modulation） is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in SSRb. The experimental results show that the short-term frequency stability of the CPT clock in SSRb is in the order of 10^-10/s and the long-term frequency stability can achieve 1.5 × 10^-11/80000s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of SSRb indicates that an atomic clock based on CPT in SSRb should be a promising candidate for making the chip scale atomic clock.     

Coherent population trapping resonance on the <Superscript>87</Superscript>Rb D<Subscript>1</Subscript> line in the field of circularly polarized counterpropagating waves

The study of the previously proposed method for improving the parameters of the coherent population trapping resonance on the ⁸⁷Rb D₁ line using two counterpropagating bichromatic fields with orthogonal circular polarizations is continued. The method consists in elimination of trap states existing in the conventional σ⁺ measurement scheme and limiting the resonance amplitude. The resonance parameters are studied in a wide range of pump radiation intensities and in various configurations implementing the σ⁺-σ^? scheme.     

On the possibility of polarizing atoms and nuclei by pulsed electromagnetic fields without using ultra-low temperatures

A method is proposed for fast and deep polarization of the system of hyperfine sublevels of the ground state of an atom having an optical excited state by means of two-component microwave pulses. The pulse of the bichromatic optical field that induces the transitions between the ground state and excited state of the atom is supposed to provide coherence among the hyperfine sublevels of the atomic ground state via the effect of coherent population trapping. The subsequent resonance microwave pulses create the polarization of equally populated ground state sublevels of the atom. The proposed polarization technique may be used for designing the new schemes of quantum computers, for the pulse transformation in optical experiments when light passes through a resonant medium containing rear-earth ions, as well as for producing polarized nuclear targets.     

基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法研究

精确的背景校正决定着冷原子吸收法检测痕量汞的检测下限,研究了基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法.汞灯光源253.65 nm共振谱线在磁场中垂直于磁场方向产生σ-,σ+和π三个线偏振光.利用超高分辨率光谱仪获取不同磁场强度下汞样品池对σ-,σ+和π线偏振光的吸光度,分析横向塞曼效应背景校正方法所需的最小磁场强度;在1.78 T强磁场强度下,分析了窄带吸收气体苯、宽带吸收气体丙酮对横向塞曼效应背景校正大气汞检测方法可能存在的干扰;利用σ-,σ+作为背景光,π线偏振光作为吸收光,对不同长度的饱和汞蒸气样品池测量,精确背景校正后,吸光度拟合曲线R值达到0.99.实验结果表明基于普通汞灯光源的横向塞曼效应背景校正大气汞检测方法可以实现精确背景校正,能够应用于大气环境痕量汞检测.