Multistep Excitation Research Articles

THE ODD PARITY AUTOIONIZING SPECTRA OF YBI

We report here the measurment and results of the odd parity autoionizing spectra of Ybl by the laser multistep excitation technique. More then thirty autoionizing levels were obtained. Our results were compared with the previous ones obtained by one photon absorption and electron collision excition technique.

Laser spectroscopy measurement of radiative lifetimes of highly excited thulium Rydberg states

The radiative lifetimes τrad of the highly excited 4f7/2136s1/2(4)np3/2[11/2](n=21−31) Rydberg Tm states have been measured with the method of multistep laser excitation and electric field ionization. The lifetime values have been obtained with an accuracy of better than 15%. The influence of blackbody radiation on the states with n ≥ 27 has been observed. The experimental results are in good agreement with our previously calculated values obtained by relativistic perturbation theory with a zero-order model approximation. It has been shown that the τrad-versus-n* dependence (n* is the effective principal quantum number) is best described by the relation τrad = 0.0022.(n*)2.46 (μsec). This property may be attributed to the strongly expressed nonhydrogenlike behavior of the investigated states, which is caused by the essentially non-Coulombic core potential acting on the Rydberg electron.

Experimental setup for multistep photoexcitation with one vacuum-ultraviolet photon as the first step

A simple experimental arrangement allowing multistep excitation studies including one VUV photon as the first excitation step is described. The system is based on the simultaneous use of a monochromatized VUV-laser plasma source with a tunable dye laser. The same pump laser is used for both excitation sources, thus allowing, if required, a well-defined time delay between the two excitation steps. The system permits both photoionization and time-resolved fluorescence measurement. Its capability is illustrated by experiments on rare gases. This demonstration shows that such a device allows one to obtain spectroscopic and kinetic information.

Tm autoionization rydberg states in the vicinity of the third and fourth atomic ionization limit

The energies of about 200 autoionization Rydberg states of the thulium atom have been measured in the 57380–58960 cm−1 energy region by laser multistep excitation and subsequent autoionization with an accuracy of ±0.4 cm−1. More than a half of the states have been grouped in series. New spectroscopic information has been derived. Three-step two-colour effective excitation schemes have been proposed for thulium atom detection.

Autoionization of Ba 6p1/2nk states in static and microwave fields below the Inglis-Teller limit.

Measurements of the autoionization rates of 6p/sub 1/2/nk states of Ba in the presence of static and 9-GHz microwave fields have been performed using a multistep laser excitation technique. For field amplitudes below 1/3n/sup 5/, which defines the Inglis-Teller limit, the measured rates in both static and dynamic fields are in good agreement with a simple Stark-effect model. The rates show an n/sup -4/ scaling rather than the familiar n/sup -3/ dependence observed in zero field. We also report the first observation of forced autoionization by microwaves. Connections between our measurements and the physical situation in plasmas are discussed, including implications for dielectronic recombination.

Laser spectroscopy of doubly excited 9sns (11

Doubly excited $ml=9s \mathrm{and} 8d$ states of Ca have been produced by multistep laser excitation via $4{\mathrm{sn}}^{\ensuremath{'}}s$ Rydberg states, and the states in which $n$ is from 20 down to $m+2$ have clearly been observed by detecting photoionization current of ${\mathrm{Ca}}^{2+}$. In some states, remarkable interference patterns and considerable line narrowing caused by the interaction with other autoionizing Rydberg series have been observed. The quantum defects of the observed states have also been obtained and discussed. In addition, we have seen some resonance peaks which are likely to be interpreted as transitions to the states with $n=m+1$ and $n=m$, although they have not definitely been assigned.

Kinetics of atoms in multistep excitation processes in plasma

Contributions to Plasma PhysicsVolume 28, Issue 4-5 p. 345-348 Article Kinetics of atoms in multistep excitation processes in plasma S. I. Krasheninnikov, S. I. Krasheninnikov I. V. Kurchatov Institute of Atomic Energy, Moscow, USSRSearch for more papers by this authorA. Yu. Pigarov, A. Yu. Pigarov I. V. Kurchatov Institute of Atomic Energy, Moscow, USSRSearch for more papers by this author S. I. Krasheninnikov, S. I. Krasheninnikov I. V. Kurchatov Institute of Atomic Energy, Moscow, USSRSearch for more papers by this authorA. Yu. Pigarov, A. Yu. Pigarov I. V. Kurchatov Institute of Atomic Energy, Moscow, USSRSearch for more papers by this author First published: 1988 https://doi.org/10.1002/ctpp.2150280412Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume28, Issue4-51988Pages 345-348 RelatedInformation

ELECTRIC FIELD EFFECTS ON Sr ATOM RYDBERG STATES

Stark structure of Sr atom Rydberg states in the vicinity of n = 12 and n = 13 were me-asured by multistep excitation method with ππ polarized lasers. The Stark map exhibited the linear behaviour of Stark manifold of Sr atom in low electric field. The crossing and antic-rossing structure of levels, which depends on the quantum effects, were discussed.

Rydberg and autoionization tm states investigation by the three-step laser excitation and electric field ionization method

The energies of 190 Rydberg and autoionization 4f13 6snp-states of the Tm atom (ground electron configuration 4f13 6s2, nuclear chargeZ=69) have been measured by the laser multistep excitation with subsequent electric field ionization method. The investigation range of these states has been extended towards states with higher and lower values of the principal quantum number. As a result the energies of 160 states have been obtained for the first time. The experiment has been carried out on an automated laser photoionization spectrometer. The measurement accuracy has been ±0.5 cm−1.

Distorted-wave impulse approximation and coupled-channels analysis of inelastic pion scattering from 18O.

Data for inelastic pion scattering from $^{18}\mathrm{O}$ at ${T}_{\ensuremath{\pi}}$=164 MeV, exciting the lowest ${2}^{+}$, ${3}^{\mathrm{\ensuremath{-}}}$, and ${1}^{\mathrm{\ensuremath{-}}}$ states, were analyzed by distorted-wave impulse approximation and coupled-channel calculations using transition densities derived from shell model calculations. Coupled-channels effects were found to be relatively unimportant for the ${2}^{+}$ and ${3}^{\mathrm{\ensuremath{-}}}$ states, but non-negligible for the excitation of the ${1}^{\mathrm{\ensuremath{-}}}$ state. Nevertheless, the inclusion of multistep excitation paths is not sufficient to generate a fit to the ${1}^{\mathrm{\ensuremath{-}}}$ data with the shell model wave functions. Major modifications are needed in the radial dependence of the neutron and proton parts of the transition density for the ${0}^{+}$\ensuremath{\rightarrow}${1}^{\mathrm{\ensuremath{-}}}$ one-step process.

Doubly excited states

Multistep laser excitation makes it possible to excite one electron at at time in the excitation of doubly excited states. This suppresses the direct continuum excitation, removing the familiar Beutler–Fano interference profiles from the excitation of autoionizing states. Removing this complexity in the excitation process allows one to investigate inherently complex atomic systems, such as interacting autoionizing series. The ability to examine such systems experimentally has led to the development of theoretical techniques based on quantum-defect theory to interpret the experimental results. This powerful combination of complementary experimental and theoretical techniques has led to substantial advances in the study of autoionizing states.

MEASUREMENT OF THE (5p3/2ns)1 AND (5p3/2nd)3 AUTOIONIZING LEVELS OF STRONTIUM BY THE MULTI-STEP EXCITATION TECHNIQUE

The (5p3/2ns)1 (n = 13-21), (5p3/2nd)3 (n = 13-24) autoionizing levels of strontium have been measured by the laser multi-step excitation method and polarization technique. In the core excitation profiles for the (5p3/2ns)1 states below the 5p1/2 ionization limit, distortions appear at locations corresponding to the (5p1/2ns), and (5p1/2nd)1 levels. Distortions also appear in the (5p3/2nd)3 excitation profiles. These results show that there exist interse-ries interactions between the (5pjns) and (5pjnd) autoionizing series of strontium.

Electronic excitation migration and trapping among cationic porphyrins adsorbed on anionic vesicle surface. Fractal-like behaviors

Picosecond time-correlated single-photon-counting studies have been made on the electronic excitation migration among positively charged porphyrins, TAPP (5,10,15,20-tetrakis(4-trimethylammonio)phenyl)porphyrin, tosylate) and ZnTMPyP (zinc 5,10,15,20-tetrakis(1-methyl-4-pyridinyl)porphyrin, chloride), adsorbed on a negatively charged surface of DHP (dihexadecyl phosphate) vesicles and its trapping at porphyrin aggregates (dimer or higher associates). The observed fluorescence decay curves cannot be reproduced by decay functions derived assuming single-step transfer from porphyrin monomer to nonfluorescent aggregate uniformly distributed in two dimensions or three dimensions. The decay function for the case of single-step transfer derived on the basis of the fractal theory is also unable to reproduce the results. It has been confirmed that the fluorescence decay function derived for multistep excitation migration on fractal and fast trapping at the first trap encounter can reproduce satisfactorily the observed results, and the fracton dimension relevant to porphyrin monomer distribution on the vesicle has been estimated to be 1.65.

Algebraic treatment of multistep excitation processes in collective nuclei: (III). Medium energy proton scattering

Channel coupling effects in the excitation of collective nuclear states with medium energy protons are analysed within the framework of the Glauber theory. The collective excitations are treated using the interacting boson model. A comparison is made between experimental and calculated cross sections for excitation of J π = 0 +, 2 + states in 154Sm.

Algebraic treatment of multi-step excitation processes in collective nuclei: (II). Electromagnetic excitation of collective nuclear states

Multi-step collective quadrupole excitations in nuclei are described using an algebraic method which does not require a coupled-channel calculation. Adiabatic effects are discussed. Applications to the axially-symmetric deformed rotor, anharmonic quadrupole vibrator, and γ-soft rotor, as well as to transitional nuclei, are presented using the consistent- Q formulation of the interacting boson model.

Evidence for multistep processes in proton capture reactions.

Proton capture populating the ${(7/2)}^{\mathrm{\ensuremath{-}}}$ second-excited state in $^{7}\mathrm{Be}$, at an excitation energy of 4.57 MeV, is reported for the $^{6}(\mathit{p}$,\ensuremath{\gamma}${)\mathrm{}}^{7}$Be reaction at a bombarding energy of 44.4 MeV. This state cannot be populated by either a conventional direct or semidirect process. Evidence is presented showing that this state could be populated via a multistep excitation in the entrance channel.

Anomalous saturation curves in laser-induced fluorescence

This is partly a tutorial and partly a review paper (with a few original additions) on saturation curves (SC) which describe the dependence of fluorescence intensity on laser intensity in atomic spectroscopy. The interest in SCs stems from applications in analytical chemistry, plasma diagnostics, physical and chemical kinetics, etc., as well as from their fundamental implications. After a brief introduction, some general facts and basic assumptions regarding atom-laser interactions are critically examined (Section 2.1) and the concepts of the “ideal” SC and saturation parameter are defined (Section 2.2). In the following Sections 3–7 various effects are discussed that can distort the SC and shift the (apparent) saturation parameter. The effects of a spatially, a temporally and a spectrally inhomogeneous laser beam, of laser-enhanced chemical reactions and ionization processes, of an optically thick atomic vapour and of various non-steady-state processes are successively reviewed. Atom trapping and polarization effects on the SCs measured recently with an atomic Na beam in vacuo are reported and discussed in some detail. Also, some new observations at high resolution on the spectrum of pulsed and cw multimode dye lasers are reported. In Section 8 some general conclusions are drawn and warnings given, and the possible extension of the concept of SC to multiphoton and multistep excitation processes, as well as to optogalvanic spectroscopy, is suggested.

Heavy-ion inelastic scattering from deformed nuclei

Theoretical and experimental methods for studying heavy-ion inelastic scattering from deformed nuclei are described. The theoretical methods involve classical-limit approximations, while particle- γ-spectroseopy techniques are employed experimentally. With these approaches, heavy-ion excitation in the Coulomb-nuclear interference region acquires a transparent interpretation, despite the apparent complexity of the multistep excitation processes involved. The examples discussed provide a good illustration of the relationship between classical and quantum physics. The sensitivity of the inelastic scattering to details of the surface ion-ion potential due to radial and angular localization is exploited to provide a method of determining the equipotential contours in a direct manner which bypasses particular model-dependent parametrizations. The method is used to construct ion-ion potentials from inelastic scattering data for the systems 40Ar + 160Gd, 156Gd, 162Dy, 164Dy, and 180Hf. The contribution of adiabatic giant resonance polarization to this potential is discussed. The relation between the deformed ion-ion potential and nuclear shapes is illustrated by comparing the experimental potentials to deformed double-folding and deformed proximity-potential calculations.

Critical remarks on a scaling law for inner-shell ionization

In superheavy quasimolecules the number of created 1sσ-vacancies per collisionsP 1sσ can be evaluated approximately by a simple scaling law. This analytical relation correctly reproduces the measured dependence ofP 1sσ on the impact parameter, bombarding energy and combined nuclear chargeZ=Z 1+Z 2. It is emphasized, however, that the absolute ionization magnitude is underestimated typically by a factor of four. This discrepancy has been successfully resolved by the inclusion of multi-step excitation processes. It is shown that the derivation of the normalization constant in a scaling law previously reported by Armbruster's group is incorrect in the framework of first order perturbation theory.

Laser atomic photoionization spectral analysis of element traces

A new method for determining trace amounts of elements in a substance has been developed. It is based on thermal evaporation and atomization of a substance in vacuum and detection of the released trace atoms by the laser stepwise photoionization technique. A rather effective way of detecting atoms is their multistep excitation to Rydberg states by the radiation of tunable dye lasers with their subsequent ionization by electric field pulses. The analytical laser spectrometer consisting of several tunable, pulsed dye lasers, a vacuum chamber with an atomizer and a recording system is described. The microimpurities of elements have been detected in pure materials: the contents of Na impurities in CdS crystals (2×10−6%) and Al impurities in germanium (2×10−7%). The detection limit of about 10−9% was determined. A technique for direct determination of the content of elements in natural water and human blood is described. A high sensitivity, universality and other merits of the method enable it to be used in determining traces of many important elements at a level of 10−8 to 10−11% almost in any matrix.