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1.
C. Vadla K. Niemax V. Horvatic 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(2):139-147
The energy-pooling rate coefficient for the
process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination
line and the metastable atoms in the 6s5d state were produced due to radiative and collisional depopulation of the laser-excited 6s6p state. The measurements were performed at number densities of about and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to
the trip let metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing
the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line
791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single
mode ring dye laser. The rate coefficient was found to be at .
Received: 11 April 1997 / Revised: 24 September 1997 / Accepted: 10 December 1997 相似文献
2.
Isotope separation by laser deflection of an atomic beam is limited in its efficiency by the accumulation of atoms in metastable states. This restriction can be removed with the use of lasers which excite metastable atoms to states from which spontaneous decay to the ground state is allowed. This is demonstrated in the separation of barium isotopes, where efficiency was improved from a lower limit of 70% to at least 83% using a second laser. Efficiency approaching 100% can be achieved in barium with a second laser but the required wavelength is not available. 相似文献
3.
By means of the Doppler-Shift-Laser-Fluorescence technique we have measured the effect of oxygen coverage on the velocity distributions and relative yields of sputtered Ba atoms and ions in both the ground and metastable excited states. Our measurements show no evidence that the excitation probabilities are correlated with the magnitude of the electric-dipole-moment matrix element to the ground state. We also find that the excitation probability of the Ba(1 D) state from a clean metal surface depends strongly on the emission velocity υ and approaches the functional form exp at higher velocities. 相似文献
4.
Separation of isotopes of barium has been accomplished by laser deflection of a single isotopic component of an atomic beam.
With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s2
1S0− 6s6p1P1 5536 Å resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large
enough to physically separate them from the atomic beam.
It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can
be separated, is determined by the branching ratio from the excited state into metastable states. In barium, repeated absorptions
and emissions on the 5536 Å transition eventually result in decay from the 6s6p1P1 state to the metastable 6s5d1D2 state. This was observed to occur for all but 3% of the138Ba atoms. As a result, the efficiency of separation was about 0.7 for the 8 mrad atomic beam divergence employed. (Throughput
was nearly 1 mg/day. No attempt was made to maximize this value.)
The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty.
The effects of near resonant atomic scattering and excitation exchange on isotopic purity are considered.
Work performed under the auspices of the U.S. Energy Research & Development Administration. 相似文献
5.
B. Jana A. Majumder P. T. Kathar A. K. Das V. K. Mago 《Applied physics. B, Lasers and optics》2011,102(4):841-849
The kinetics of a two-step photoionization process in optically thick atomic medium of barium (Ba) is studied using the rate equation approach. In the first step, Ba atoms get resonantly excited by laser radiation from their ground state to an intermediate excited state and subsequently are ionized in the second step by another laser radiation. The absorption of exciting radiation is taken into account along its propagation direction (optically thick). However, the medium is assumed to be optically thin for the ionizing radiation. A numerical simulation is done to estimate the ionization yield for time-varying Gaussian shaped laser pulses. The required energy density of the laser pulse to saturate the excitation transition throughout the thick medium is calculated. The effect of optical delay between the laser beams on the ionization yield is simulated. The calculated ionization yield from the simulation is compared with the measured values. 相似文献
6.
本文基于无任何可调参数的势模型计算了碱土金属原子(Be、Mg、Ca、Sr、Ba)与Ne原子间相互作用势,得到的势能曲线及势阱位置和深度与现有的从头计算结果符合较好.本文的计算结果进一步验证了碱土金属原子与稀有气体原子间交换能主要来自碱土金属原子最外层s电子与稀有气体原子最外层p电子之间的交换作用. 相似文献
7.
We have measured the radiative lifetime of the (5d6p)3D3 state of barium by Hanle effect. This state was populated by cw dye laser excitation of an atomic beam of Ba in the metastable (5d6s)3D3 state. The metastable state was populated by a dc discharge. With dye laser excitation, the shape of the Hanle effect curve is strongly modified due to optical pumping of the metastable state. A brief discussion of the expected and observed signal shapes is given. The radiative lifetime of the (5d6p)3D3 state is measured to be τ = 10.2 ± 1.5 ns. 相似文献
8.
A. Camposeo O.M. Maragò B. Fazio B. Klöter D. Meschede U. Rasbach C. Weber E. Arimondo 《Applied physics. B, Lasers and optics》2006,85(4):487-491
Resist-assisted atom lithography with group III elements, specifically with gallium and indium, is demonstrated. Self-assembled monolayers (SAM) of nonanethiols prepared on thin sputtered gold films were exposed to a beam of neutral gallium and indium atoms through a physical mask. The interaction of the Ga and In atoms with the nonanethiol layer, followed by a wet etching process, creates well defined structures on the gold film, with features below 100 nm. The threshold of the lithographic process was estimated by optical methods and found to be around 3 gallium atoms and 12 indium atoms per thiol molecule. Our experiments suggest that resist-assisted atom lithography can be realized with group III elements and possibly extended to new neutral atomic species. PACS 07.77.Gx; 42.82.Cr; 81.16.Ta 相似文献
9.
A possibility of CW laser oscillation on atomic transitions between a resonance energy level and a metastable one under conditions when lower laser states are deactivated by electron impacts has been theoretically shown. We determined the plasma parameters so that CW laser action on such transitions of Cu, Au, Ca and Ba atoms may be possible. Superlong laser pulses of 6 μs duration were obtained on the 6 1P1-5 1D2 transition of the barium atom. 相似文献
10.
The static and dynamic electric dipole, quadrupole, and octupole polarizabilities of the alkaline-earth atoms (beryllium, magnesium, calcium, strontium, and barium) in the ground state were calculated. The dynamic polarizabilities obtained were used to calculate the van der Waals coefficients C 6, C 8, and C 10 of alkaline-earth metal dimers for the interaction of two like atoms in the ground state. The results are compared with other theoretical and experimental data. 相似文献
11.
利用流体模型模拟研究了氦气空心阴极放电的时空动力学过程,计算得到了不同放电时刻电子和亚稳态氦原子密度、电势、电场、基态电离速率和分步电离速率等的时空分布特性。特别是讨论了亚稳态原子和分步电离对于放电的影响。结果表明,随着电流的增长,放电处于五个不同的放电模式:第一阶段电流上升非常缓慢,为汤生放电模式,带电粒子密度、亚稳态原子密度和径向电场均很弱;第二阶段电流迅速上升,放电模式由汤生放电向空心阴极放电过渡,带电粒子密度、亚稳态原子密度和径向电场迅速增强;第三阶段达到准稳态阶段,放电电流增长速度变缓,形成了明显的阴极鞘层结构;第四阶段为空心阴极效应形成阶段,向稳态阶段过渡;第五阶段为稳态放电阶段。研究结果同时表明,亚稳态氦原子和分步电离在放电的初始阶段对于放电的发展作用较弱,在前三阶段中,电子的产生以基态电离为主。随着放电的发展,由亚稳态原子引起的分步电离对新的电子产生的作用逐渐接近并超过基态电离,对总电离的贡献率越来越高。 相似文献
12.
E. Yu. Remeta V. I. Kelemen A. N. Zavilopulo A. V. Snegurskii 《Journal of Experimental and Theoretical Physics》2000,90(2):250-257
The spectroscopy of metastable states is used to make the first experimental measurement of the total differential elastic-scattering cross sections of metastable helium atoms in 23 S and 21 S states by sodium atoms in the ground state at interaction energy 68 meV in the center-of-mass system. To analyze the experimental data, the partial scattering phases are calculated using the method of phase functions in the optical potential approximation. The analysis makes it possible to give a more detailed interpretation of the structure of the differential cross section. The computed integral cross sections, specifically, Penning ionization, diffusion, viscosity, and spin exchange are discussed. 相似文献
13.
The multiphoton transitions in atomic Ba are experimentally studied in the presence of strong off-resonant radiation that generates additional atomic polarization in the ground state. It is demonstrated that the additionally induced polarization of the Ba atoms in the ground state leads to a higher probability of the multiphoton transitions from this state. 相似文献
14.
For an argon glow discharge in a 1 mm thick cell at room temperature, we have observed the absorption spectrum of the 1s3–2p2 (Paschen notation) line by using a diode laser. It is found that, with a decrease in the gas pressure below 0.1 Torr, the linewidth drastically decreases; at 0.02 Torr the velocity distribution of the metastable atoms in the surface normal direction has an apparent temperature of 144 K. The velocity distribution is also found to be anisotropic: the spectrum profile depends on the direction of observation with respect to the surface normal. These phenomena are explained by a model in which the velocity distribution of the metastable atoms is controlled by collisional quenching at the wall surface and velocity-changing collisions with ground state atoms. 相似文献
15.
16.
K. Suchanek M. Suchanek A. Nikiel T. Pałasz M. Abboud A. Sinatra P.-J. Nacher G. Tastevin Z. Olejniczak T. Dohnalik 《The European physical journal. Special topics》2007,144(1):67-74
An accurate optical method to measure the nuclear
polarization of 3He atoms in the 11S ground state is
described. The absorption of a weak, probe laser beam is used to
measure the relative populations of two hyperfine sublevels of the
23S metastable state that are not addressed by the pumping
laser beam. Since a common spin temperature between the ground and
metastable states is established by metastable exchange
collisions, the nuclear polarization can be derived from these
absorption measurements. The method is highly sensitive, robust,
and can be used to monitor the dynamics of optical pumping and
relaxation processes without interfering with them. It was
successfully implemented and tested in the 0.45–2.0 T magnetic
field range at the 3He gas pressure up to 67 mbar. 相似文献
17.
Multiphoton transitions in the Ba atom are experimentally studied in the presence of strong nonresonant radiation that additionally polarizes atoms in the ground state. It is found that the additionally induced polarization of Ba atoms leads to an increase in the probability of multiphoton transitions from this state. 相似文献
18.
The scattering of metastable 23S He atoms (He*) from cleaved NiO(100) as well as from clean and CO-covered Cu(100) surfaces has been studied. For these varied surfaces, which were characterized in situ by ground state He atom scattering, only broad He* angular distributions without any diffraction peaks were observed. For metastable He atoms scattered from the clean Cu(100) surface a total survival probability of 1×10−6 was determined. For NiO(100) and the CO-covered Cu(100) surface values of about 1×10−5 were obtained. Time-of-flight spectra of the surviving He* atoms revealed a substantial energetic broadening which increases with the substrate temperature. This behaviour indicates a large well depth for the He*–surface interaction potential and is discussed in terms of an enhanced multiphonon excitation and/or trapping probability upon the scattering. 相似文献
19.
20.
A simple relation between the copper halide laser output and the densities of ground state (2S) and metastable state (2D) copper atoms was found. This relation was used to analyze the experimental results of Nerheim. In all the analyzed systems it was found that about four percent of the ground state copper atoms take part in the lasing process. This may have implications for the efficiency of copper halide lasers. 相似文献