Experimental study on multiphoton ionization of Ar with high intensity short laser pulses

<正>We present high resolution photoelectron energy spectra from multiphoton ionization(MPI) of Ar subject to laser pulses with wavelength of 400 nm,pulse duration of 35 fs,and maximum intensity of 5×10~(13) W/cm~2.Ionizations into Ar~+ ~2P_(3/2) and ~2P_(1/2) channels are observed and distinct resonance structures are found in both ionization channels.The intensity dependence of the resonance structures is explained in terms of the mechanism of Freeman resonance,i.e.,transient resonances of alternating current (AC) Stark-shifted Rydberg states at specific intensities within the laser pulse.     

Chaotic ionization of nonhydrogenic alkali Rydberg states

We report the first ab initio quantum treatment of microwave driven alkali Rydberg states. We find that nonhydrogenic atomic initial states exhibit fingerprints of classically chaotic excitation, and identify the cause of their experimentally observed enhanced ionization, as compared to Rydberg states of atomic hydrogen.     

Matter-wave interferometry with atoms in high Rydberg states

Matter-wave interferometry has been performed with helium atoms in high Rydberg states. In the experiments the atoms were prepared in coherent superpositions of Rydberg states with different electric dipole moments. Upon the application of an inhomogeneous electric field, the different forces on these internal state components resulted in the generation of coherent superpositions of momentum states. Using a sequence of microwave and electric field gradient pulses the internal Rydberg states were entangled with the momentum states associated with the external motion of these matter waves. Under these conditions matter-wave interference was observed by monitoring the populations of the Rydberg states as the magnitudes and durations of the pulsed electric field gradients were adjusted. The results of the experiments have been compared to, and are in excellent quantitative agreement with, matter-wave interference patterns calculated for the corresponding pulse sequences. For the Rydberg states used, the spatial extent of the Rydberg electron wavefunction was ～320?nm. Matter-wave interferometry with such giant atoms is of interest in the exploration of the boundary between quantum and classical mechanics. The results presented also open new possibilities for measurements of the acceleration of Rydberg positronium or antihydrogen atoms in the Earth's gravitational field.     

Application of electric field ionization method to detect the high-lying Rydberg states of Eu I

The 4f~76s(~9S)np 8 P J (J = 5/2, 7/2, 9/2) Rydberg series converging to the first ionization limit 4f 7 6s 9 S 4 of the Eu atom using the three-step laser excitation and electric-field-ionization (EFI) method are studied. First, the Eu atom is excited from the 4f 7 6s 2 8 S o 7/2 ground state to the 4f 7 6s7s 8 S o 7/2 state through the 4f 7 6s6p 10 P 9/2 state by the first two dye lasers. Next, it is populated to many higher-n members of the 4f 7 6s( 9 S)np 8 P J Rydberg series by the third dye laser whose wavelength is scanned within a certain range. Finally, the atom in these higher-n states is ionized by the external pulsed electric field. With the field strength up to 2 kV/cm, we can detect the atom in 4f 7 6s(9 S)np 8 P J states with n 40. With the given laser line width, the level energies of Rydberg states with n as high as 72 can be determined. We not only confirm the previous data on the 4f 7 6s(9 S) np 8 P J Rydberg series, but also extend the n-value assignment significantly by detecting more states.     

Asymmetry in the strong-field ionization of Rydberg atoms by few-cycle pulses

We present measurements of the electron ejection direction in the ionization of high (n=90) Rydberg states of rubidium subjected to few-cycle radio-frequency (RF) pulses. For weak pulses we find a strong asymmetry for even (cosine) pulses and no asymmetry for odd (sine) pulses. This asymmetry disappears for pulses longer than four RF cycles. For strong pulses, very large asymmetry is found for both sine and cosine pulses that persists up to eight RF cycles and is attributed to initial state depletion effects within a cycle.     

Engineering very-high-n polarized Rydberg states using tailored half-cycle-pulse sequences

We show that strongly polarized very-high-n (n approximately 600) potassium Rydberg atoms can be produced by manipulating lower-n (n approximately 350) polarized atoms using a tailored sequence of ultrashort half-cycle pulses (HCPs). The protocol for this involves first a weak HCP that generates transient phase-space localization whereupon a second large HCP of opposite polarity excites the electron to a broad distribution of highly elongated states. This distribution is then refocused by a short periodic train of HCPs using the properties of (un)stable manifolds near fixed points in phase space.     

Ionization and population transfer in lithium Rydberg states with ultrashort chirped laser pulses

We present a theoretical study of dynamics of Rydberg states of lithium using ultra short chirped laser pulse having a Gaussian envelope. The population transfer probabilities are calculated of different Rydberg states on chirped laser factors. The calculations are performed by direct numerical integration of Schr?dinger equation using fourth order Runge-Kutta method. The behavior of dynamics of Rydberg states for these factors is of great significance. These results are of potential interest in coherent quantum control, quantum computation and in many physical and chemical processes.     

Electric dipole moments of lithium atoms in Rydberg states

Recently, the diverse properties of Rydberg atoms, which probably arise from its large electric dipole moment(EDM),have been explored. In this paper, we report electric dipole moments along with Stark energies and charge densities of lithium Rydberg states in the presence of electric fields, calculated by matrix diagonalization. Huge electric dipole moments are discovered. In order to check the validity of the EDMs, we also use these electric dipole moments to calculate the Stark energies by numerical integration. The results agree with those calculated by matrix diagonalization.     

Lifetimes of high Rydberg states of methyl halides

The lifetimes of high Rydberg states of the methyl halides CH₃I, CH₃Br and CH₃Cl have been studied. A pulsed dye laser tuned near half the ionization energy was used, with preprogrammed field pulses, and the high Rydberg states of the compounds in selected ranges of n values were ionized after a variable delay. Plots of the electron signal versus delay yielded information about the Rydberg state lifetime. The clearest trend was found for around n = 120–160: the lifetimes of the states decreased by more than an order of magnitude from CH₃I (τ ≈12.3 μs) through CH₃Br to CH₃C1. Within the range studied, the theoretically predicted increase in lifetimes (n ⁵ or n ³) was not found, and in fact the highest group of states studied (with n > 215) exhibited for all three compounds relatively short lifetimes (≈2-3 μs), possibly due to collisional processes.     

Field ionization process of Eu 4f~76snp Rydberg states

The field ionization process of the Eu 4f76 snp Rydberg states, converging to the first ionization limit, 4f76s9S4, is systematically investigated. The spectra of the Eu 4f76 snp Rydberg states are populated with three-step laser excitation, and detected by electric field ionization(EFI) method. Two different kinds of the EFI pulses are applied after laser excitation to observe the possible impacts on the EFI process. The exact EFI ionization thresholds for the 4f76 snp Rydberg states can be determined by observing the corresponding EFI spectra. In particular, some structures above the EFI threshold are found in the EFI spectra, which may be interpreted as the effect from black body radiation(BBR). Finally, the scaling law of the EFI threshold for the Eu 4f76 snp Rydberg states with the effective quantum number is built.     

微波场中里德堡锂原子的高激发跃迁

运用含时多态展开方法研究微波场中里德堡锂原子高激发态的性质,得到锂原子在微波场中的跃迁几率,实现对量子态的操纵与控制.结果表明:选择合适的振幅、频率等参数,可以实现布居数在量子态之间的完全跃迁.     

啁啾微波场中里德伯钠原子高激发态的布居跃迁

采用含时多态展开方法, 结合B样条函数和单电子原子模型势研究微波场中钠原子里德伯高激发态的性质, 得到钠原子的能级结构及在微波场中的布居数迁移, 实现对量子态的操纵与控制. 结果表明: 含时多态展开方法结合B样条函数和单电子原子模型势是有效研究微波场中碱金属原子性质的一种方法; 选择合适的啁啾率、振幅等参数, 可以实现布居数在量子态之间的完全迁移和量子态囚禁.     

微波场中里德堡锂原子的高激发跃迁

运用含时多态展开方法研究微波场中里德堡锂原子高激发态的性质,得到锂原子在微波场中的跃迁几率,实现对量子态的操纵与控制。结果表明：选择合适的振幅、频率等参数,可以实现布居数在量子态之间的完全跃迁。     

氩原子共振增强多光子电离谱--奇对称性里德堡态

利用脉冲放电产生氩原子亚稳态4s2[3/2]°2和4s′2[1/2]°0,在610～670nm波长范围内,利用共振增强多光子电离和飞行时间质谱技术得到氩原子(2+1)REMPI谱.光谱分析表明所有谱线来源于氩原子4s2[3/2]2和4s′2[1/2]°0两个亚稳态向16个奇对称性里德堡态双光子跃迁,并标识所有谱线.同时首次在实验上观察到一个长序列的3p54s′2[1/2]°0→3p5nd2[1/2]°1(n=8～31)双光子跃迁.在实验技术上,提供了一种研究惰性气体原予以及其它原子高里德堡态和自电离态的新方法.