High resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency

We have presented a high resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency (EIT). The EIT spectrum in the $\Xi$-type configuration is usually companied by a double resonance optical pumping (DROP) due to the strong optical coupling between the two upper states, leading to the spectral lines seriously deformed and widely broadened for complex relaxation processes in DROP. Here we demonstrate a high resolution spectroscopy by far-detuning EIT for $^{87}\rm{Rb}$ $\rm{5S_{1/2}\rightarrow5P_{3/2}\rightarrow5D_{5/2}}$ in magnetic fields. The method of far-detuning eliminates the relaxation in DROP to the most extent and decreases the spectral linewidth from more than 20 MHz down to its natural linewidth limit (6 MHz). The deformation of the spectral lines also disappears and the observed spectra are well in accordance with the theoretical calculation. Our work shows that far-detuning EIT is a reliable high resolution spectroscopic method when the relaxation in DROP cannot be neglected, especially for the case of transition to low excited states.     

An effective quantum defect theory for the diamagnetic spectrum of a barium Rydberg atom

A theoretical calculation is carried out to investigate the spectrum of a barium Rydberg atom in an external magnetic field. Using an effective approach incorporating quantum defect into the centrifugal term in the Hamiltonian, we reexamine the reported spectrum of the barium Rydberg atom in a magnetic field of 2.89 T [J. Phys. B 28 L537 (1995)]. Our calculation employs B-spline basis expansion and complex coordinate rotation techniques. For single photon absorption from the ground 6s2 to 6snp Rydberg states, the spectrum is not influenced by quantum defects of channels ns and nd. The calculation is in agreement with the experimental observations until the energy reaches E = 60 cm-1 . Beyond this energy, closer to the threshold, the calculated and experimental results do not agree with each other. Possible reasons for their discrepancies are discussed. Our study affirms an energy range where the diamagnetic spectrum of the barium atom can be explained thoroughly using a hydrogen model potential.     

强子–强子碰撞中硬分量存在的又一实验证据

对sqr(s)=540Gev能量下的高能强子-强子碰撞得到的单事件平均横动量p. 对多重数N的散点图进行了仔细分析后指出;其中大多重数、大事件是碰撞过程中出现硬分量的又一个实验证据,并用仅含软分量的单分量模型和既含软分量又含硬分量的二分量模型的Monte Carlo模拟定性地证实了这一论断.     

飞秒时间分辨质谱方法研究CF3I光电离动力学

利用飞秒双色泵浦 探测 (pump probe)飞行时间质谱方法研究了CF3 I分子多光子电离动力学 ,所用泵浦光及探测光的中心波长分别为 2 6 5和 398nm .获得了母分子离子CF3 I+ 信号及其碎片离子CF3 + 和I+ 信号的寿命衰减常数分别为 (96± 7)、(198± 13)和 (16 7± 6 )fs.这些离子产生的多光子通道机理不同 :CF3 I来自 (1+2′)跃迁 ,单光子泵浦光与CF3 IA带共振 ;驭光子泵浦光激发CF3 I分子到 5 pπ7sδ(2 Π1/ 2 )里德伯态 ,单光子探测光电离产生的母分子离子解离产生CF3 + ;I+ 来自 (2 +2′)和 (1+1′ +2′)激发过程     

Tunneling between double wells of atom in crossed electromagnetic fields

The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model. The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin. A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory, at B=0.8~T and F=-220~V.cm^-1. The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well, making it possible to penetrate the quantum information of the outer well. However, the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.     

Photodetachment of H- near an elastic surface in a magnetic field

This paper investigates the photodetachment of the negative hydrogen ion H near an elastic wall in a magnetic field.The magnetic field confines the perpendicular motion of the electron,which results in a real three-dimensional well for the detached electron.The analytical formulas for the cross section of the photodetachment in the threedimensional quantum well are derived based on both the quantum approach and closed-orbit theory.The magnetic field and the elastic surface lead to two completely different modulations to the cross section of the photodetachment.The oscillation amplitude depends on the strength of the magnetic field,the ion-wall distance and the photon polarization as well.Specially,for the circularly polarized photon-induced photodetachment,the cross sections display a suppressed(E E th) 1/2 threshold law with energy E in the vicinity above Landau energy E th,contrasting with the(E E th) 1/2 threshold law in the presence of only the magnetic field.The semiclassical calculation fits the quantum result quite well,although there are still small deviations.The difference is attributed to the failure of semiclassical mechanics.     

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.     

Scaled-energy spectroscopy of a ｜M｜= 1 Rydberg barium atom in an electric field

We observe strong energy-dependent quantum defects in the scaled-energy Stark spectra for |M| = 1 Rydberg states of barium atoms at three scaled energies: ε = 2.000,ε = 2.500 and ε = 3.000.In an attempt to explain the observations,theoretical calculations of closed orbit theory based on a model potential including core effect are performed for non-hydrogenic atoms.While such a potential has been uniformly successful for alkali atoms with a single valence electron,it fails to match experimental results for barium atoms in the 6snp Rydberg states with two valence electrons.Our study points out that this discrepancy is due to the strong perturbation from the 5d8p state,which voids the simple approximation for constant quantum defects of principle quantum number n.     

CO LMR spectrum of ~(14)N~(16)O and its analysis with spectra of ~(14)N~(17)O and ~(14)N~(18)O

LMR spectra for v=1←0 transitions of 14N16O in X2Π1/2,3/2 states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund's case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of 14N16O as well as 14N17O and 14N18O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1 -2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of 14N17O and 14N18O were deduced.     

飞秒泵浦-探测质谱方法研究苯内转换动力学

以飞秒 40 0及 2 66nm激光脉冲结合泵浦 探测飞行时间质谱方法研究了苯S2 态内转换动力学 .40 0nm双光子过程将苯分子激发到S2 电子态 ,布居在S2 电子态的分子由于能级耦合无辐射弛豫到S1电子态 .通过测定C6 H6 +讯号强度随泵浦 探测延迟时间的改变 ,获得苯S2 及S1电子态的衰减寿命分别为 ( 48± 1)fs及 ( 6.5± 0 .2 )ps ,S2 态及S1电子态的消激发机理被认为是相应势能面间的锥形交叉引起的内转换