铯原子气室中D2线泵浦探测光谱的实验观测

在铯原子气室中采用偏振方向相互垂直且同向传播的线偏泵浦光和探测光，研究了铯原子D2线的泵浦探测光谱。由于在6 S1/2 F=3 – 6 P3/2 F’=2 超精细跃迁中存在多个L型塞曼子能级结构，从而产生了电磁诱导透明导致的吸收减弱；而在6 S1/2 F=4 – 6 P3/2 F’=5 超精细跃迁中则观测到了电磁诱导吸收。通过改变泵浦光的失谐量，在电磁诱导透明形成的吸收减弱凹陷和电磁诱导吸收产生的吸收增强峰内部均观察到了反常的吸收信号反转。     

Rb87基态超精细塞曼能级跃迁的偏振激发特性

本论述了Rb^87基态超精细塞曼能级光泵磁共振的偏振激发特性,给出了塞曼能级跃迁谱线随抽运光偏振特性的变化。     

Rb原子滤波器的实验研究

本文用热Rb原子进行了光学滤波的研究。将一束激光调谐到Rb原子D2线的F=1→F′=2共振吸收线上,使其泵浦Rb原子,实现原子布居极化(即将Rb原子制备到能级F=2上)。当一束信号光反向穿过该介质时,若信号光频率调谐到原子"吸收窗口"(D1线F=2→F′=2),该介质对信号光大量吸收,信号光透射率仅为0.14%;若信号光频率调谐到原子"透明窗口"(D1线F=1→F′=2),信号光透射率高于47.4%。这种极化的原子介质可以用来做光学滤波器。     

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.     

利用原子的塞曼光谱对半导体激光器进行稳频

中性原子的超精细能级在磁场中产生塞曼分裂 ,另外 ,左旋和右旋圆偏振光激发下原子的跃迁选择定则不同 ,因此 ,原子在超精细塞曼能级间的吸收谱峰相对无磁场条件下的吸收谱峰有一定的移动。利用这一点 ,验证了一种简单、灵活的方法对半导体激光器进行稳频 ,使激光器的线宽稳到小于 1MHz。通过对实验结果的分析 ,发现由左旋和右旋圆偏振光激发引起的原子吸收谱峰移动之和与饱和吸收峰半高宽相等时 ,稳频效果最好     

自旋轨道耦合玻色爱因斯坦凝聚体中的拉曼耦合强度

对玻色爱因斯坦凝聚中拉曼跃迁的拉比频率和耦合强度进行了实验研究,拉比频率是光与原子相互作用中的一个重要参量,用于衡量原子与光场之间耦合强度的大小,而拉曼跃迁耦合强度是自旋轨道耦合实验中的一个重要参数。研究了不同拉曼光频率失谐下,87 Rb在F=1时的超精细塞曼子能态|1,0〉和|1,1〉间的拉曼跃迁拉比振荡。在800nm的拉曼光作用下,观测到超精细态F=2的5个塞曼能态间同时耦合的拉比振荡。该工作有助于87 Rb自旋轨道耦合实验中参数的优化选择。     

宽波段连续调谐全固态CW PPMgLN光学参量振荡器

利用半导体激光泵浦输出1064 nm波长的全固态连续Nd:YVO4激光器作为泵浦源,采用周期调谐和温度调谐组合调谐技术,对基于掺氧化镁周期性极化铌酸锂晶体（MgO:LiNbO3, PPMgLN）准相位匹配（QPM）的全固态连续波（CW）光学参量振荡器（OPO）宽波段无分立连续调谐输出特性进行研究。实验采用连续工作模式和外腔结构,基于多周期PPMgLN晶体的30.2,30.4和30.6 m周期,在改变晶体的极化周期的基础上,同时在30～100 ℃范围内调节晶体工作温度。实验结果表明:CW PPMgLN OPO的泵浦阈值仅为0.22 W;不同极化周期需要的温度调谐范围不同;信号光在1 559.8～1 597.2 nm近红外波段和闲频光在3 187.3~3 347.3 nm中红外波段连续调谐输出。实现了外腔式全固态CW OPO在信号光和闲频光波段的无分立连续调谐输出。     

光子晶体光纤产生飞秒超连续谱的实验研究

研究了飞秒脉冲经过光子晶体光纤时超连续谱产生的物理机制。采用输出波长可调谐的钛宝石光参量放大器作为泵浦源,光纤光谱仪测量不同泵浦功率和不同泵浦波长条件下光子晶体光纤产生的超连续谱的光谱图,对进行了归一化处理后的不同泵浦功率和不同泵浦波长条件下的超连续谱进行对比,分析影响光子晶体光纤超连续谱差异的物理机制。实验结果表明,当泵浦波长不变时,随着入射泵浦脉冲平均功率的增大,波峰增多,谱宽也逐渐加宽并伴随着出现能量向短波方向集中的现象,泵浦功率到达一定强度时,超连续谱的宽度最后到达饱和,谱的包络趋于稳定;入射光功率稳定在300 mW时,超连续谱的宽度和形状皆受到泵浦波长影响,在760～840 nm范围内,泵浦波长越长,波峰数越多,泵浦脉冲波长离零色散点越近,光子晶体光纤产生的超连续谱谱宽会越宽,超连续谱的形状相对越平坦。     

室温下铯原子气室中6P_(3/2)-8S_(1/2)激发态跃迁的速度选择光谱

以室温下的气室铯原子为介质,采用泵浦探测的方法获得激发态之间的光谱.在泵浦光与探测光相向、同向作用于铯原子得到的激发态超精细光谱有很大的差异.当考虑多普勒效应的影响,其分析结果与实验结果相一致.     

520nm泵浦780nm+1560nm双共振光学参量振荡器

我们在实验中演示了520nm单频绿光泵浦的基于周期极化磷酸钛氧钾(PPKTP)晶体的780nm+1560nm双共振光参量振荡器,高效制备780nm+1 560nm连续可调谐双色下转换光场。该参量振荡器可输出93.3 mW的1 560nm单频激光和44.6mW的780nm单频激光。通过改变PPKTP晶体的温度所得到的波长粗调范围为:信号光1 529.81nm~1 573.83nm(~44nm),闲置光788.26nm~777.20nm(~11nm);通过连续调谐520nm泵浦激光频率初步得到的闲置光在780.24nm(铷原子D2线)处频率连续调谐范围约1.6GHz。     

Optical pumping and population transfer of nuclear-spin states of caesium atoms in high magnetic fields

Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti:sapphire laser in a magnetic field of 1.516T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification \delta a(\bm S \cdot \bm I) of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change \delta a(\bm S \cdot \bm I) of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.     

Spin polarization of two-dimensional electron system in different Laughlin states and around filling factor

The spin configuration of the ground state of a two-dimensional electron system is investigated for different FQHE states from an analysis of circular polarization of time-resolved luminescence. The method clearly distinguishes between fully spin polarized, partially spin polarized and spin unpolarized FQHE ground states. We demonstrate that FQHE states which are spin unpolarized or partially polarized at low magnetic fields become fully spin polarized at high fields. Temperature dependence of the spin polarization reveals a nonmonotonic behavior at . At and the electron system is found to be fully spin polarized. This result does not indicate the existence of any skyrmionic excitations in high magnetic field limit. However, at the observed spin depolarization of electron system at and becomes broader for lower magnetic fields, so that full spin polarization remains only in a small vicinity of . Such a behavior could be considered as a precursor of skirmionic depolarization, which would dominate for smaller ratios between Zeeman and Coulomb energies.We demonstrate that the spin polarization of 2D-electron system at and can be strongly affected by hyperfine interaction between electrons and optically spin-oriented nuclears. This result is due to the fact that hyperfine interaction can both enhance and suppress effective Zeeman splitting in fixed external magnetic field.     

Quantized Magnetic Flux in the Bohr–Sommerfeld Model

Based on the Bohr–Sommerfeld model, we investigate the quantization of magnetic flux through the electronic orbits together with its dependence on additional sources of magnetic fields. The additional magnetic field causes changes of the angular momentum and hence shifts of the energy of the atomic levels. We study this effect for the cases of the Zeeman effect, where the source is an external homogeneous magnetic field, and the hyperfine interaction, where the source is the field of the magnetic moment of the nucleus. We discuss a model for the handling of the different angular momentum contributions for which the energy shifts due to the Zeeman effect and the magnetic dipole contribution to the hyperfine interaction can be reproduced quite well. The meaning of “spin,” however, changes within this approach drastically. The unusual Landé g-factor of the electron is discussed to be the result of a reduced ground-state angular momentum of the electron in combination with the field of the magnetic moment of the electron rather than an intrinsic property of the electron.     

Atomic coherence effects on optically pumped cesium atoms in static magnetic field

The population difference between ground states F = 4 and F = 3 is calculated for Cs atoms pumped on the D₂ line by a resonant laser beam. The pumping efficiency for Cs atoms in a static magnetic field on two hyperfine transitions (6S_1/2 F = 4 → 6P_3/2 F′ = 3 and F′ = 4) is calculated for various pump laser intensities. The population difference as a function of the static magnetic field exhibits a dip centered at the zero magnetic field, which corresponds well with the Zeeman coherence between sublevels of the F = 4 state. The full-width at half-maximum (FWHM) of the dip as a function of the pump laser intensity shows abnormal power broadening behavior that differs for different hyperfine transitions. We present experimental results that agree with the theoretical calculations.     

Electron and nuclear spin interactions in the optical spectra of single GaAs quantum dots

Fine and hyperfine splittings arising from electron, hole, and nuclear spin interactions in the magneto-optical spectra of individual localized excitons are studied. We explain the magnetic field dependence of the energy splitting through competition between Zeeman, exchange, and hyperfine interactions. An unexpectedly small hyperfine contribution to the splitting close to zero applied field is described well by the interplay between fluctuations of the hyperfine field experienced by the nuclear spin and nuclear dipole/dipole interactions.     

Using a new method to solve the single-electron atom problem

A new relativistic method of one-component wave functions applicable for describing fields with arbitrary spins is suggested. This method is used to solve the problem of energy states of hydrogen-like atoms with different required accuracies and under differing conditions (rough estimate, relativistic correction, fine structure, Zeeman effect in a magnetic field, or hyperfine splitting with account of nucleus spin)     

Sublevel spectroscopy of alkali atoms in superfluid helium

We report the results of optical pumping and optical detection of magnetic resonance of alkali atoms (Cs and Rb) in superfluid helium. The magnetic resonances between the ground-state Zeeman sublevels and hyperfine levels are observed through monitoring theD ₁ fluorescence by means of the optical-rf double resonance technique. Although the ground stateg values in superfluid helium are the same as in vacuum within the experimental error, the hyperfine constant of the ground state of the Cs atom in superfluid helium is found to be slightly larger than in vacuum. Coherent transient spectroscopy is also performed.     

Controlling electronic spin relaxation of cold molecules with electric fields

We present a theoretical study of atom-molecule collisions in superimposed electric and magnetic fields and show that dynamics of electronic spin relaxation in molecules at temperatures below 0.5 K can be manipulated by varying the strength and the relative orientation of the applied fields. The mechanism of electric field control of Zeeman transitions is based on an intricate interplay between intramolecular spin-rotation couplings and molecule-field interactions. We suggest that electric fields may affect chemical reactions through inducing nonadiabatic spin transitions and facilitate evaporative cooling of molecules in a magnetic trap.     

Study of atomic spectral lines in a magnetic field with use of a nanocell with the thickness <Emphasis Type="Italic">L</Emphasis> = λ

We propose a technique which we call “L = λ Zeeman technique” (LZT) for investigation of the transitions between the Zeeman sublevels of the hfs structure of alkali metal atoms in external magnetic fields. The technique is based on the employment of a nanocell with the thickness of the Rb atom vapor column equal to the wavelength of the laser radiation, 780 nm, resonant with the atomic rubidium D₂ transition. At the laser intensities of about 1 mW/cm² in the transmission spectrum of the nanocell narrow (～ 30 MHz) resonant peaks of reduced absorption appear localized exactly on the atomic transitions. In magnetic fields these peaks are split and their amplitudes and frequency positions depend on the magnetic field strength. The theoretical model well describes the experimental results.     

Effective hyperfine temperature in frustrated Gd 2Sn 2O 7: two level model and 155Gd Mössbauer measurements

Using ¹⁵⁵Gd M?ssbauer spectroscopy down to 27 mK, we show that, in the geometrically frustrated pyrochlore Gd₂Sn₂O₇, the Gd³⁺ hyperfine levels are populated out of equilibrium. From this, we deduce that the hyperfine field, and the correlated Gd³⁺ moments which produce this field, continue to fluctuate as T ↦ 0. With a model of a spin 1/2 system experiencing a magnetic field which reverses randomly in time, we obtain an analytical expression for the steady state probability distribution of the level populations. This distribution is a simple function of the ratio of the nuclear spin relaxation time to the average electronic spin-flip time. In Gd₂Sn₂O₇, we find the two time scales are of the same order of magnitude. We discuss the mechanism giving rise to the nuclear spin relaxation and the influence of the electronic spin fluctuations on the hyperfine specific heat. The corresponding low temperature measurements in Gd₂Ti₂O₇ are presented and discussed. Received 17 October 2001 Published online 6 June 2002