A 2-dimensional detector with high spatial and temporal resolution for metastable rare gas atoms

We describe a detector for metastable rare gas atoms which allows the investigation of transverse atomic beam distributions on the single atom level with lateral dimensions of 1 m, which occur frequently in the field of atom optics. In contrast to existing detection techniques, the conversion step from the metastable atom to an electron is separated from the charge amplification to improve spatial resolution. The conversion is performed at a metal surface, which is followed by an electron-optical system imaging the electron distribution with a proper magnification onto a single electron detection unit. The spatial resolution that we achieve with this technique is on the order of 1 m, the temporal resolution on the order of 1 s. The application of the detector for atom interferometry is discussed. Received: 22 May 1996 / Revised version: 21 June 1996     

Gain and lasing of optically pumped metastable rare gas atoms

Optically pumped alkali vapor lasers are currently being developed in several laboratories. The objective is to construct high-powered lasers that also exhibit excellent beam quality. Considerable progress has been made, but there are technical challenges associated with the reactivity of the metal atoms. Rare gas atoms (Rg) excited to the np(5)(n+1)s (3)P(2) configuration are metastable and have spectral properties that are closely similar to those of the alkali metals. In principle, optically pumped lasers could be constructed using excitation of the np(5)(n+1)p←np(5)(n+1)s transitions. We have demonstrated this potential by observing gain and lasing for optically pumped Ar(*), Kr(*) and Xe(*). Three-level lasing schemes were used, with He or Ar as the collisional energy transfer agent that established the population inversion. These laser systems have the advantage of using inert reagents that are gases at room temperature.     

Inelastic processes in the scattering of metastable rare gas atoms at metal surfaces

Electron spectra of various metastable rare gas atoms systematically measured on a Pt(111) surface with Rb coverages ranging from submonolayers (3%) to multilayers are presented. The different decay channels of the excited particles are discussed in terms of resonant electron exchange processes between the substrate and the projectile in relation to the work function. It is shown that below a certain value of the work function a highly excited negative rare gas atom is formed which can undergo different de-excitation processes. A careful discussion of the branching ratios into the decay channels offers a natural explanation of the variations in the electron spectra induced by alkali metal adsorption. Additionally, an attempt is made to extract information about the alkali metal chemisorption state from the observed electron spectra.     

Electron emission from crystal surfaces of condensed aromatics under the impact of metastable rare gas atoms

Energy distributions of electrons ejected from polycrystalline surfaces of naphthacene, perylene and coronene by the impact of metastable He ^*, Ne ^* and Ar ^* atoms have been measured. Two types of peaks, which are similar to the “non-moving” and “moving” structures in photoelectron spectra, are observed in each spectrum. The non-moving structures (ca. 1 eV) for perylene and coronene are similar to those in the photoelectron spectra, whereas the relative intensities of the two non-moving structures for naphthacene (0.6 and 1.7 eV) are remarkably different from the corresponding structures in the photoelectron spectrum. The peak positions (but not necessarily their intensities and widths) for the moving structures for all the samples (> 2 eV) agree with those of the corresponding photoelectron spectra. The origin of these moving structures is ascribed to Penning ionization on the solid surface.     

Interactions of rare gas cations with lighter rare gas atoms

High-level ab initio calculations are employed to generate potential energy curves for rare gas cations, RG⁺, interacting with neutral atoms of other rare gases, RG′, that are lighter (RG′ = Ne–Rn). The calculations employ the RCCSD(T) method, with doubly-augmented basis sets of quintuple-ζ quality. The interaction potential curves, with the full counterpoise correction applied, are calculated point-by-point. Spin-orbit coupling is applied analytically in an atom-based model. The potentials are used to calculate spectroscopic parameters, which are then compared to recent experimental work, and the very limited previous theoretical work. In addition, the potentials are used to calculate ion transport properties and the ion mobilities are compared to the few experimental data available.     

An investigation of high fractions of metastable helium atoms

Penning type discharge was adopted to excite helium atoms. It is suitable for generating high density metastables at a range from 0.1 mTorr to 0.5 Torr. The highest metastable density of 3.5 x 1010 cm-3 was observed at a static gas pressure of 0.5 Torr. The highest fraction of metastables (N12s/Nhe) of 10-3 in a low gas pressure was obtained. The variation of the magnetic field strength on the discharge does not result in a significant density change of the metastable helium atoms. When no magnetic field was applied, no discharge took place.     

Radial Sternheimer shielding-antishielding for rare gas atoms

The radial dependence of Sternheimer quadrupole shielding-antishielding factor is reported for He, Ne, Ar and Kr atoms at the coupled Hartree-Fock level of accuracy. The results would be useful in the interpretation of the nuclear quadrupole interactions measured at the rare gas nuclei in different chemical environment such as the various van der Waals molecules.     

Excitons in rare gas atoms and solids

Excitons in rare gas are described using the integral equation approach and an appropriate semi-empirical simplification of the short-range terms. In the solids, polarization effects are taken into account using a semi-continuum model in analogy with F-centre problem. Reasonable agreement with experiments is obtained for exciton binding energy shifts passing from atoms to crystals.     

Electron collisions with laser cooled and trapped metastable helium atoms: total scattering cross sections

Absolute measurements of total scattering cross sections for low energy (5-70 eV) electrons by metastable helium (2(3)S) atoms are presented. The measurements are performed using a magneto-optical trap which is loaded from a laser-cooled, bright beam of slow He(2(3)S) atoms. The data are compared with predictions from convergent close coupling and R matrix with pseudostate calculations, and we find good agreement between experiment and theory.     

Vacuum ultraviolet resonance line radiation source from rare gas atoms and ions for UHV photoelectron spectroscopy

A source and differential pumping system for producing high intensity resonance line radiation from rare gas atoms and ions for ultrahigh vacuum (UHV) photoelectron spectroscopy has been developed. Photoelectron count rates from a gold sample, as measured with a double-pass cylindrical mirror analyzer at pass energy 15 eV and 0.10 eV resolution, are ～ 300,000 c s^?1 for the He(I) (21.22 eV) line and ～30000 c s^?1 for the He(II) (40.81 eV) line. The source design is based on the principle of the electrostatic charged particle oscillator and is capable of sustaining discharges over the pressure range 1 to ～ 10^?6 torr. The discharge segment consists of a cylindrical cold cathode surrounding two tungsten rod anodes which are held at high positive potential. Three stages of differential pumping are employed in order that the vacuum in the main spectrometer chamber can be maintained at 2 × 10^?10 torr during operation. The calculated helium flow reaching the main chamber under these conditions is < 101 s^?1. Details of the construction and operating characteristics of the source are presented.     

Interaction of rare gas atoms with metal surfaces: A pseudopotential approach

The pseudopotential formulation of the helium-metal surface interaction due to Harris and Liebsch has been generalized to treat the heavier rare gases. The atom-surface repulsion is calculated to first-order in the pseudopotential and is combined with a damped van der Waals interaction to produce the total physisorption potential. Reasonable results are obtained for all the rare gases considered, with a systematically increasing potential-well depth through the rare gas sequence. A single surface-atom model is also considered and its limitations discussed.     

Lifetime of metastable fluorine atoms

For laser collimation of neutral F atoms, a resonance transition cycle between the metastable and the upper excited states (3s⁴ P _5/2?3p⁴ D ⁰ _7/2) can be used as a two-level closed system. We have determined the lifetime of the metastable state (3s⁴ P _5/2) in F atoms by measuring the decay curve of the fluorescence intensity as a function of distance from the plasma source. Combining the measured velocity of F radicals from the Doppler shift of the fluorescence peak, we have obtained the lifetime of the F metastable state as 3.7±0.5 μs. With this short metastable lifetime of F radicals, the simple Doppler cooling method using spontaneous light force is not practical for laser collimation of F radicals. Use of stimulated light force may be necessary to collimate F radical beams in a short distance. Received: 4 July 2000 / Published online: 13 September 2000     

The short range interactions between two rare gas atoms

The short range interactions in He₂, Ne₂ and Ar₂ have been studied in terms of the electronic forces as functions of their internuclear separations employing their single configuration SCF wave functions. The results show that the constituent molecular orbitals behave differently in terms of the forces they exert on the nuclei during the interaction process. The different behaviour of the orbitals is also reflected in the redistribution of charges.     

半导体泵浦亚稳态惰性气体激光器理论建模与性能分析

建立了半导体泵浦亚稳态惰性气体激光器(DPRGL)速率方程模型,以Ar为例,仿真分析泵浦强度、亚稳态原子数密度以及增益介质长度对DPRGL工作性能的影响。结果表明:高泵浦强度(约kW/cm2)条件下DPRGL理论上具有大于55%的光-光效率;亚稳态原子数密度和增益介质长度对激光器性能影响具有等价性;实际中需综合优化泵浦强度、亚稳态原子数密度、增益介质长度等激光器参量以实现激光器最大的光光转换效率。     

Deexcitation of sputtered metastable aluminum atoms

An experimental system was set up incorporating pulsed ion beam sputtering, two Nd:YAG pumped dye lasers and an imaging time-of-flight (TOF) analysis system. The system was used to perform state-selective analyses of neutral atoms sputtered from surfaces using resonant one-color and two-color ionization schemes. We have measured, for the first time, TOF mass spectra of Al atoms sputtered into the ground state and first excited state (with an excitation energy of 0.014 eV) from single crystals of Ni₃Al and NiAl. The population ratio of the first excited state to the ground state in the sputtered flux was estimated to be 0.91 for Ni₃Al and 0.95 for NiAl, respectively. This indicates that the magnitude of the excitation energy plays an important role even in the deexcitation rate of sputtered metastable state atoms with an open outer shell.     

半导体泵浦亚稳态惰性气体激光器理论建模与性能分析

建立了半导体泵浦亚稳态惰性气体激光器（DPRGL）速率方程模型,以Ar为例,仿真分析泵浦强度、亚稳态原子数密度以及增益介质长度对DPRGL工作性能的影响。结果表明：高泵浦强度（约kW/cm2）条件下DPRGL理论上具有大于55%的光-光效率;亚稳态原子数密度和增益介质长度对激光器性能影响具有等价性;实际中需综合优化泵浦强度、亚稳态原子数密度、增益介质长度等激光器参量以实现激光器最大的光光转换效率。     

Degenerate Bose-Fermi mixture of metastable atoms

We report the observation of simultaneous quantum degeneracy in a dilute gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3 (fermion) by helium-4 (boson), both in the lowest triplet state, allows us to produce ensembles containing more than 10(6) atoms of each isotope at temperatures below 1 microK, and achieve a fermionic degeneracy parameter of T/TF = 0.45. Because of their high internal energy, the detection of individual metastable atoms with subnanosecond time resolution is possible, permitting the study of bosonic and fermionic quantum gases with unprecedented precision. This may lead to metastable helium becoming the mainstay of quantum atom optics.     

Magnetic trapping of metastable helium atoms

Metastable helium atoms were efficiently transferred from a magneto-optical trap (MOT) to a magnetic quadrupole trap, producing samples of up to 3᎒⁷ magnetically trapped atoms at a temperature of about 1 mK. We observe purely exponential decay of the samples with time constants of 9-10 s and derive an upper bound for the rate coefficient of inelastic Penning collisions.