铯Rydberg原子Stark态的避免交叉

在磁光阱中利用双光子激发制备49S铯Rydberg原子,研究了超冷49S态原子在外加电场中的Stark效应和nS态原子与(n-4)多重态之间的避免交叉现象.利用态选择脉冲场电离方法测量并获得了避免交叉点附近的离子谱,测量了避免交叉点附近离子谱的变化情况,并观察到避免交叉点附近由相互作用导致的态转移现象.     

Efficient Rydberg positronium laser excitation for antihydrogen production in a magnetic field

Antihydrogen production by charge exchange reaction between positronium (Ps) and antiprotons requires an efficient excitation of Ps atoms up to high-n levels (Rydberg levels). We propose a two-step laser light excitation, the first from ground to n?=?3 and the second from this level to a Rydberg level n?>?15. In this study it is assumed that a Ps cloud is produced by positrons hitting a target converter located in a Penning-Malmberg trap within a uniform ~ 1 T magnetic field. We model the optical transition structure by taking into account Doppler and motional Stark effects. The predicted efficiency for population deposition in high n states is of ~30%.     

The dynamics of a THz Rydberg wavepacket

An optically excited Rydberg wavepacket can be generated by exciting the electron from a low-lying state to a coherent superposition of high-lying states with a short broadband optical pulse. A special kind of Rydberg wavepacket is generated in the case of a interaction of a weak THz half cycle pulse with a stationary Rydberg state, called the THz wavepacket. This THz wavepacket is a coherent superposition of the initial Rydberg state and its neighbouring states. We have investigated the time evolution of THz wavepackets by measuring the impact of two in time delayed half cycle pulses ( ≈ 200 V cm^-1) on the population of a stationary (n = 40) Rydberg state in rubidium. The first half cycle pulse creates the THz wavepacket and the second half cycle pulse probes the dynamics of the THz wavepacket. We support our experimental data by numerically solving the Schr?dinger equation and with a semi-classical picture. Whereas an optically excited wavepacket is initially localized, a THz wavepacket is initially delocalized and becomes localized after half a revival time. Received 23 August 2000 and Received in final form 27 March 2001     

The break of L-S coupling and the double Stark resonance in the spectrum of 36P → 37P two-photon transition in Rydberg atoms of sodium

New results are presented of an experimental investigation of the spectrum of 36P → 37P two-photon microwave transition in Rydberg atoms of sodium in a constant electric field. Depending on the conditions of excitation of the initial 36P state (the constant electric field is switched on either before or after the exciting laser pulse) and polarization of laser radiation, a strong variation is observed of the amplitudes of individual two-photon transitions between the fine-structure Stark components of the 36P and 37P states. This effect is an analog of the Paschen-Back effect in a strong magnetic field and is due to the break of L-S coupling and to the variation of the wave functions of Rydberg electrons in an electric field. It is also found that the break of L-S coupling affects considerably the shape of double Stark resonance arising upon intersection of the virtual intermediate level of two-photon transition with the real intermediate 37S level.     

Three photon resonant ionization in atomic potassium via S,P, D and F series Rydberg states

Single colour three photon resonant ionization (2 + 1) is observed in atomic potassium vapour in a heat pipe oven using an excimer laser pumped dye laser. Using wavelengths between 570 nm and 603 nm various²S and²D Rydberg states are populated by two photon excitation. Third photon of the same wavelength ionizes the atoms. Rydberg states up ton ⋍ 50 are observed. Electric field as low as 1 V/cm causes extensive Stark mixing of the states. This results in progressively higher three photon ionization signals via the perturbed²P and²F Rydberg states. The three photon ionization process is studied using both linearly and circularly polarized incident light. The experiment shows qualitatively that the²P Rydberg states are perturbed primarily by the²D states in the prescence of an external electric field and to a much smaller extent by²S states. This is also explained theoretically by calculating the Stark mixing coefficients under the Bates and Daamgard (1949) approximation. Implication for a similar effect in other alkali elements is discussed.     

Population coherent control of Rydberg potassium atom via adiabatic passage

The time-dependent multilevel approach(TDMA) and B-spline expansion technique are used to study the coherent population transfer between the quantum states of a potassium atom by a single frequency-chirped microwave pulse.The Rydberg potassium atom energy levels of n=6-15,l=0-5 states in zero field are calculated and the results are in good agreement with other theoretical values.The time evolutions of the population transfer of the six states from n=70 to n=75 in different microwave fields are obtained.The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters.     

High resolution laser spectroscopy of Ba Rydberg atoms

The purpose of the present paper is to illustrate some selected aspects of high resolution laser spectroscopy of Rydberg atoms, rather than giving an extensive review of the state of the art. The following topics will be discussed: (i) Excitation and detection of Ba Rydberg atoms with principal quantum numbers up ton≲300; (ii) Stark effect and atomic diamagnetism of high-n Ba Rydberg states in thel-mixing region, (iii) Resonance in singlet-triplet mixing of 6snp¹P₁ and 6snd¹D₂ Ba Rydberg states deduced from hyperfine structure measurements.     

Detection and study of Rb I Rydberg states

We describe the details of an experiment using an atomic beam of rubidium which allowed us to detect by field ionization techniques the np Rydberg states from n = 28 up to n = 78, to detect also ns and nd states using a Stark mixing, and for all of these detected states to check the classical law E_c = [16n^*4]^?1 concerning the critical ionizing electric field E_c. It turns out that for n as high as 65 this law is quite well verified.     

Second and fourth order stark shifts in the 6snd 1 D 2 barium rydberg series

Stark splittings of⁶ snd ¹ D ₂ Rydberg states were measured betweenn=10 and 24 by quantum beat spectroscopy at very low electric field strengths, allowing the determination of tensor polarizabilities and atn=14, 19, and 24 the determination of tensor hyperpolarizabilities. The irregular behaviour of the tensor polarizabilities was explained by Coulomb approximation calculations. The fourth order contributions to the Stark Hamiltonian were written as effective operators. Representation in spherical tensor form gives tensors of rank zero, two, and four. The associated scalar and tensor hyperpolarizabilities were derived. Using these formulae, theoretical values for the hyperpolarizabilities were calculated.     

Population coherent control of Rydberg sodium atom in microwave field

The B-spline expansion technique and the time-dependent multilevel approach (TDMA) are used to study the interaction between microwave field and sodium atoms. The Rydberg sodium atom energy levels of p states in zero field are calculated, and the results are in good agreement with the other theoretical ones. The time evolutions during the population transfers of the five states from n=75 to n=79 in different microwave fields are obtained. The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters.     

Effect of photoions on the line shape of the Förster resonance lines and microwave transitions in cold rubidium Rydberg atoms

Experiments are carried out on the spectroscopy of the Förster resonance lines Rb(37P) + Rb(37P) → Rb(37S) + Rb(38S) and microwave transitions nP → n′S, n′D between Rydberg states of cold rubidium atoms in a magneto-optical trap (MOT). Under ordinary conditions, all spectra exhibit a linewidth of 2–3 MHz irrespective of the interaction time between atoms or between atoms and microwave radiation, although the limit resonance width should be determined by the inverse interaction time. The analysis of experimental conditions has shown that the main source of line broadening is the inhomogeneous electric field of cold photoions that are generated under the excitation of initial nP Rydberg states by broadband pulsed laser radiation. The application of an additional electric-field pulse that rapidly extracts photoions produced by a laser pulse leads to a considerable narrowing of lines of microwave resonances and the Förster resonance. Various sources of line broadening in cold Rydberg atoms are analyzed.     

超冷nS Rydberg原子的态转移

本文从实验上研究了超冷nS Rydberg原子在外电场脉冲作用下的态转移现象. 采用双光子激发超冷基态原子制备超冷Rydberg原子, 通过脉冲场电离法探测超冷Rydberg原子的离子信号, 实验研究了由外加脉冲电场产生的nS能级和多重态的避免交叉, 获得了在外电场脉冲作用下nS态原子的态转移现象, 实验与理论计算的结果相一致. 关键词： Rydberg原子 态转移 能级避免交叉     

Study of the electric field and wall voltage in a high pressure ac-PDP cell by laser induced fluorescence spectroscopy

The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5－50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.     

Transfer of a weakly bound electron in collisions of Rydberg atoms with neutral particles. II. Ion-pair formation and resonant quenching of the Rb(nl) and Ne(nl) States by Ca, Sr, and Ba atoms

Electron-transfer processes are studied in thermal collisions of Rydberg atoms with alkaline-earth Ca(4s ²), Sr(5s ²), and Ba(6s ²) atoms capable of forming negative ions with a weakly bound outermost p-electron. We consider the ion-pair formation and resonant quenching of highly excited atomic states caused by transitions between Rydberg covalent and ionic terms of a quasi-molecule produced in collisions of particles. The contributions of these reaction channels to the total depopulation cross section of Rydberg states of Rb(nl) and Ne(nl) atoms as functions of the principal quantum number n are compared for selectively excited nl-levels with l ? n and for states with large orbital quantum numbers l = n ? 1, n ? 2. It is shown that the contribution from resonant quenching dominates at small values of n, and the ion-pair formation process begins to dominate with increasing n. The values and positions of the maxima of cross sections for both processes strongly depend on the electron affinity of an alkaline-earth atom and on the orbital angular momentum l of a highly excited atom. It is shown that in the case of Rydberg atoms in states with large l ～ n ? 1, the rate constants of ion-pair formation and collisional quenching are considerably lower than those for nl-levels with l ? n.     

啁啾微波场中里德伯锂原子的相干激发与控制

运用含时多态展开方法和B-样条函数研究了微波场中里德伯锂原子高激发态的性质,得到锂原子量子态n=70-75,l=0-5的能量,并分析了里德伯锂原子高激发态n=70-75,l=0-5在微波场中的跃迁几率.结果表明:通过优化微波场参数可以实现量子系统从初始态到目标态的完全跃迁,且在跃迁过程中,每个l态都起至关重要的作用.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

Stark spectrum of barium in highly excited Rydberg states

We present observations of Stark spectra of barium in highly excited Rydberg states in the energy region around n = 35. The one-photon excitation concerns the π transition. The observed Stark spectra at electric fields ranging from 0 to 60 V·cm-1 are well explained by the diagonalization of the Hamiltonian incorporating the core effects. From the Stark maps, the anti-crossings between energy levels are identified experimentally and theoretically. The time of flight spectra at the specified Stark states are recorded, where the deceleration and acceleration of barium atoms are observed. This is very consistent with the prediction derived from the Stark maps from the point of view of energy conservation.     

Electric-field induced dipole blockade with Rydberg atoms

High resolution laser Stark excitation of np (60相似文献