Radiative lifetimes of highly excited states in rubidium
2014 Measurements have been made of the natural radiative lifetimes of highly excited rubidium (9 ~ n ~ 18) S and D states. These results, as well as those already published concerning P and F states, agree well with the theoretical lifetimes calculated by the Bates-Damgaard method. J. Physique 41 (1980) 119-121 1 FTVRIER 1980, Classification Physics Abstracts 32.70 In the past few years, measurements of the radiative lifetimes of highly excited states of alkali atoms have been reported [1-3]. These results would clearly be of interest for physicists working in atomic physics, plasma physics, astrophysics. Moreover they allow interesting comparisons with theoretical calculations. We have already published measurements of the radiative lifetimes for some Rydberg P and F states in rubidium [4, 5]. In order to obtain a consistent set of lifetime values for a given alkali atom, we present here measurements concerning the nS and nD states of rubidium (9 n 18). Comparison is given between the obtained experimental values and the theoretical ones calculated by using a modified Bates-Damgaard Method [6, 7] (here after refered as B.D.). We use the classical method of time resolved laser induced fluorescence [4]. Rubidium atoms contained in a cell are excited in a given high-lying nS or nD state by stepwise pulsed excitation via the first resonant 5P state. For convenience the 5p3,2 state is chosen as the intermediate state for the excitation of the nS levels, the observation of the population decay being made on the nS -+ 5P 1/2 line. The nD states are produced by using light pulses whose wavelengths correspond either, to the 5PI/2 --+ nD3/2 transitions for n 13, or to the 5P3/2 -+ nD3/2,5/2 transitions for n &#x3E; 13; the population decay is observed on these same lines. Such a choice is determined by the fact that we are also interested in the study of some collisional properties of the nD states (results concerning the collisional properties of both the S and D levels will be published elsewhere [8]). Thus our reported lifetimes refer to the nD3/2 states for n 13 and to the nD states, without allowance for fine structure, for n &#x3E; 13. This is of no importance since the lifetimes corresponding to the two fine structure levels are expected to be very close, for a given n value. A high-speed photon counting system allows the determination of the decay of the excited.state population as a function of time for a given rubidium pressure. The extrapolation to zero rubidium pressure yields the natural radiative lifetime. The experimental set-up, shown in figure 1, has been already widely Fig. 1. Experimental set-up. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01980004102011900
Multichannel quantum defect theory of strontium bound Rydberg states
Using the reactance matrix approach, we systematically develop new multichannel quantum defect theory (MQDT) models for the singlet and triplet S, P, D and F states of strontium below the first ionization limit, based on improved energy level measurements. The new models reveal additional insights into the character of doubly excited perturber states, and the improved energy level measurements for certain series allow fine structure to be resolved for those series’ perturbers. Comparison between the predictions of the new models and those of previous empirical and ab initio studies reveals good agreement with most series; however, some discrepancies are highlighted. Using the MQDT wave functions derived from our models we calculate other observables such as Landé g J ?> -factors and radiative lifetimes. The analysis reveals the impact of perturbers on the Rydberg state properties of divalent atoms, highlighting the importance of including two-electron effects in the calculations of these properties. The work enables future investigations of properties such as Stark maps and long-range interactions of Rydberg states of strontium.
On the theory of collisions of atoms in rydberg states with neutral particles
2014 The theory of transitions between Rydberg states induced by thermal collisions, and of the broadening and shift of optical lines involving such states, is reconsidered. It is shown that the Fermi potential can be generalized in terms of the reaction matrix of the collision between a free electron and the neutral perturber. Adiabatic potential curves of the quasi-molecule are thus obtained in analogy with quantum defect theory. An adiabaticity criterion is proposed to distinguish between inelastic and quasi-elastic collisions. The scattering length approximation and JWKB wave-functions are used to obtain an approximate expression for cross-sections of quasi-elastic collisions (0394n = 0) for intermediate n values (n ~ 15-20). It is also shown that it is possible to explain the observed behaviour of the broadening and the shift of optical lines by noble gases and alkalis for intermediate or high n values. LE JOURNAL DE PHYSIQUE TOME 38, NOVEMBRE 1977, Classification Physics Abstracts 34.00 32.70