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     

Femtosecond interatomic Coulombic decay in free neon clusters: large lifetime differences between surface and bulk

A quantitative determination of 2s vacancy lifetimes in surface and bulk atoms of free Ne clusters has been made. While for free atoms the 2s inner-valence hole has a ps lifetime, it reduces to 6+/-1 fs for cluster bulk atoms. For surface atoms, the lifetime is on average longer than 30 fs. The lifetime estimate was obtained from fits of high-resolution photoelectron spectra of Ne clusters. The shortening of the lifetime is attributed to the coordination dependent interatomic Coulombic decay, which is extremely sensitive to internuclear distances.     

Lifetime measurement of the 9s level of atomic francium

We use two-photon resonant excitation and time-correlated single-photon counting techniques on a sample of 210Fr atoms confined and cooled in a magneto-optical trap to measure the lifetime of the 9s excited level. Direct measurement of the decay through the 7P(3/2) level at 851 nm yields a lifetime of 107.53 +/- 0.80 ns.     

Measurement of atomic lifetimes with a mode-locked laser

We present a new technique for measuring atomic lifetimes with a mode-locked laser. A single laser pulse excites the atoms and a subsequent frequency-doubled pulse ionizes the excited-state atoms. The ions are collected and counted. The measurement is repeated using excitation and detection pulses with different time separations, which determines the excited-state decay rate. We demonstrated this technique for the 6P(3/2) state of cesium. The measured lifetime was 30.5 ns and had a statistical uncertainty of 0.1 ns. Systematic effects limited the overall experimental uncertainty to approximately 0.6 ns in this initial experiment.     

介质腔中自发辐射原子的寿命分布

在本文中,我们研究了半无限大介质板夹层对空腔中激发态原子的自发辐射率的影响,并利用寿命分布函数来描述原子衰变动力学的性质,在对称和非对称的结构中,分别计算了以原子在板中的相对位置为自变量的原子自发辐射率的函数,计算结果表明,原子的自发辐射率与介质腔的宽度以及外层半无限大介质板的折射率有关,介质腔可以增强或抑制激发态原子的激发,当介质腔的宽度足够大时,原子的寿命分布呈现指数衰减的形势,这些理论结果和实验值相符合的非常好.     

Polaron relaxation dynamics in InAs/GaAs self-assembled quantum dots

Polaron decay in n-type InAs quantum dots has been investigated using energy dependent, mid-infrared pump–probe spectroscopy. By studying samples with differing ground state to first excited state energy separations the relaxation time has been measured between 40 and 60 meV. The low-temperature decay time increases with increasing detuning between the pump energy and the optical phonon energy and is maximum (55 ps) at 56 meV. From the experimentally determined decay times we are able to extract a low-temperature optical phonon lifetime of 13 ps for InAs QDs. We find that the polaron decay time decreases by a factor of 2 at room temperature due to the reduction of the optical phonon lifetime.     

Processes of decay of Rydberg plasma

The lifetime of a molecule consisting of two Rydberg atoms with respect to electron release is determined from computer simulation of two classical electrons in the field of Coulomb centers. From this, the cross section of the Penning process of collision of two Rydberg atoms with electron release is obtained. The rate constant for ionization of Rydberg atoms is evaluated for the Rydberg plasma within the Thomson model. On the basis of these processes, the kinetics is analyzed for the decay of a Rydberg plasma. Comparison with experimental data shows that these decay processes are responsible for the first stage of the decay of a magnetized and nonmagnetized Rydberg plasma located in a magnetic superconducting trap, whereas other processes become important at a subsequent stage of the plasma evolution. This article was submitted by the authors in English.     

Studies of weak interaction effects by laser spectroscopy of short-lived atoms

Laser-induced nuclear orientation has been used to make sub-Doppler-resolution measurements of a nuclear isomer^85mRb that has a lifetime of only a microsecond. The technique succeeds because the sampled atoms remove themselves before equilibrating. This paper describes two cases in which pre-equilibrium removal of atoms can prevent thermal equilibrium from obscuring information about the weak interaction that is present in the velocity profile of atoms as they recoil following beta decay. It should be possible to measure electron-antineutrino angular correlations in the beta decay of⁸⁵Kr, and to look for beta decay of tritium into an atomic bound state of³He-a fundamental effect predicted by weak interaction theory but never observed.     

Decay distribution of spontaneous emission from an assembly of atoms in photonic crystals with pseudogaps

Spontaneous decay behaviors from an assembly of atoms (or molecules) in 3D photonic crystals (PC's) with pseudogaps are investigated. Theoretically, a lifetime distribution function for these atoms or molecules is defined to reveal decay kinetics. Our calculations show that quite wide or narrow lifetime distributions can occur for different spread configurations of the atoms (or molecules). The pure PC effect may lead to coexistence of both accelerated and inhibited decay processes. These results provide theoretical clarification for substantial discrepancies in the recent reported experiments.     

Time-resolved Auger decay in CsBr using high harmonics

The temperature-dependent decay dynamics of innershell holes in CsBr was measured by using high harmonics. The measured lifetime was as short as 1.5 ps at 340 K due to increasing the Auger-allowed final state density in the Urbach exciton tail, whereas it is 1.1 ns at 10 K, determined by radiative recombination. The temperature-dependent Auger lifetime extrapolated to a high temperature corresponds to the fully energy-allowed Auger decay. In the model to be presented, this yields an interatomic Auger decay lifetime of 2.4+3.8/-1.5 fs, in line with a theoretical calculation for NaF.     

NaK分子激发态的预离解和碰撞激发转移

用Ar+激光器固定频率488.0nm线激发Na-K混合蒸汽,NaK分子激发态通过自发辐射、预离解和与基态原子的碰撞激发转移而去布居,测量在不同K原子密度下原子荧光对分子荧光的强度比,结合NaK(E)态寿命,得到了预离解率和碰撞激发转移率.     

Schemes for Generating Cluster States via Cavity Systems

We propose a scheme for generating an N-atom cluster state via cavity quantum electrodynamics （ CQED）. In our scheme, there is no transfer of quantum information between the atoms and the cavity, i.e., the cavity is always in the vacuum state, so the cavity decay can be suppressed. Also, the generated cluster state is the entanglement of the ground states, so the atomic spontaneous emission can be avoided. Therefore, the cluster state generated in our scheme has a longer lifetime. Furthermore, the requirement on the quality factor of the cavity greatly loosened for the cavity is only virtually excited.     

Dynamical evolution of correlated spontaneous emission of a single photon from a uniformly excited cloud of N atoms

We study the correlated spontaneous emission from a dense spherical cloud of N atoms uniformly excited by absorption of a single photon. We find that the decay of such a state depends on the relation between an effective Rabi frequency Omega proportional square root N and the time of photon flight through the cloud R/c. If OmegaR/c<1 the state exponentially decays with rate Omega(2)R/c and the state lifetime is greater than R/c. In the opposite limit OmegaR/c>1, the coupled atom-radiation system oscillates between the collective Dicke state (with no photons) and the atomic ground state (with one photon) with frequency Omega while decaying at a rate c/R.     

DMANS——一种新型荧光闪烁体染料的寿命与能量转移的研究

本工作对一种新型荧光闪烁体染料——4-二甲胺基—4''硝基芪(DMANS)在不同介质中的光谱行为和能量转移进行了研究,发现介质的极性大小以及介质和染料间的能量转移对该闪烁体染料的荧光量子产率和闪烁发光延迟具有重大影响。研究对选择基体材料和合理组成闪烁材料配方有一定的参考价值。     

Atomic beam measurement of the lifetime of the3 P 1 metastable states of Mg and Ca

The lifetime of the metastable level³ P ₁ of Mg and Ca have been measured in an atomic beam experiment. We excite the atoms to the³ P ₁ state by electron collisions and we measure the decay length of the light emitted by the beam. The velocity distribution of the atoms is also measured by a time-of-flight technique. The decay length and the velocity measurements are then combined to compute the required lifetimes. The results are (2.4±0.2)×10^?3 sec for Mg and (0.55±0.04)×10^?3 sec for Ca.     

K(6S)+H2→K(4D)+H2的碰撞能量转移

激光双光子激发K原子至6s或4D态,测鼍了K(6S,4D)与H2的碰撞转移截面.池温在413K,H2气压在4～40 Pa范围内,K(6S,4D)-K的碰撞效应可略去.在激发6S态的情况下,记录6S→4P时间分辨荧光信号,从荧光强度的对数描绘出的直线斜率得到6S态的有效寿命,而4D态的布居随H2的增加而增加,因此引起4D→4P跃迁谱线的增强.在激发4D态的情况下,采用类似方法得到4D态的有效寿命,由Stern Volmet方程,测得6S和4D态的辐射寿命分别为(97±15)ns和(300±45)ns.激发态K原子总的碰撞去佰居截面为(1.6±0.3)×10-14cm2(对6S态)和(40±6)×10-16cm2(对4D态).该总截面中包含向K原子激发态的非反应碰撞转移截面以及与H2反应生成KH的反应截面.激发6S态,测量4D→4P的时间积分荧光强度随H2气压的变化,得到6S→4D的碰撞转移截面为(1.4±0.3)×10-14cm2.由此得到结论:K(6S)态主要是通过物理猝灭到K(4D)态,虽然在K(6S)+H2的碰撞中,观察到了由于化学反应生成的KH的存在.     

Observation of persistent flow of a Bose-Einstein condensate in a toroidal trap

We have observed the persistent flow of Bose-condensed atoms in a toroidal trap. The flow persists without decay for up to 10 s, limited only by experimental factors such as drift and trap lifetime. The quantized rotation was initiated by transferring one unit variant Planck's over 2pi of the orbital angular momentum from Laguerre-Gaussian photons to each atom. Stable flow was only possible when the trap was multiply connected, and was observed with a Bose-Einstein condensate fraction as small as 20%. We also created flow with two units of angular momentum and observed its splitting into two singly charged vortices when the trap geometry was changed from multiply to simply connected.     

Bose-Einstein condensation of metastable helium

We have observed a Bose-Einstein condensate in a dilute gas of 4He in the (3)2S(1) metastable state. We find a critical temperature of (4.7+/-0.5) microK and a typical number of atoms at the threshold of 8 x 10(6). The maximum number of atoms in our condensate is about 5 x 10(5). An approximate value for the scattering length a = (16+/-8) nm is measured. The mean elastic collision rate at threshold is then estimated to be about 2 x 10(4) s(-1), indicating that we are deeply in the hydrodynamic regime. The typical decay time of the condensate is 2 s, which places an upper bound on the rate constants for two-body and three-body inelastic collisions.     

Lifetime of core two-hole states in atoms

The lifetime of core two-hole states in atoms is discussed using an atomic many-body theory. The lifetime widths of the two-hole states with the core holes in the Lx (X = l–3) shells of Ar atom are calculated by an ab initio atomic many-body theory (Green's function method using the extended random-phase approximation with exchange (RPAE)). The present theory gives good agreement with experiment. The changes not only in the Coster-Kronig electron kinetic energy but also in the polarization effect on the Coster-Kronig electron by the presence of extra two holes created by decay of the partner hole or by the presence of the partner hole, affects considerably the lifetime width of the two-hole state in Ar atom so that it deviates much from the sum of that of the individual hole.     

Decay lifetime and evolution of semiconductor quantum dots in photonic crystals

Spontaneous emission from GaAs/AlGaAs quantum dots (QDs) embedded in photonic crystals with a narrow photonic band gap is studied theoretically. The results show that the decay lifetime is very sensitive to the sizes of QDs, and both inhibited and accelerated emission can occur, which had been indicated in a previous experiment. The Weisskopf–Wigner approximation, good for atoms and molecules, may be incorrect for QDs. A damped Rabi oscillation of the excited state with the transition frequency outside the photonic band gap may appear, which is impossible for atoms and molecules.