Effect of photoions on the line shape of the Förster resonance lines and microwave transitions in cold rubidium Rydberg atoms

Experiments are carried out on the spectroscopy of the Förster resonance lines Rb(37P) + Rb(37P) → Rb(37S) + Rb(38S) and microwave transitions nP → n′S, n′D between Rydberg states of cold rubidium atoms in a magneto-optical trap (MOT). Under ordinary conditions, all spectra exhibit a linewidth of 2–3 MHz irrespective of the interaction time between atoms or between atoms and microwave radiation, although the limit resonance width should be determined by the inverse interaction time. The analysis of experimental conditions has shown that the main source of line broadening is the inhomogeneous electric field of cold photoions that are generated under the excitation of initial nP Rydberg states by broadband pulsed laser radiation. The application of an additional electric-field pulse that rapidly extracts photoions produced by a laser pulse leads to a considerable narrowing of lines of microwave resonances and the Förster resonance. Various sources of line broadening in cold Rydberg atoms are analyzed.     

Probabilities of radiative dipole transitions of parahelium in an electric field

Quadratic Stark corrections to the wave functions, matrix elements, and probabilities of transitions between the singlet states ¹ S ₀ and ¹ P ₁ of helium atoms are calculated. The coefficients of the polynomials that depend on the effective principal quantum number of the upper level v _f and that approximate the numerical values of the polarizabilities, the quadratic corrections to the wave functions, and the probabilities of transitions to highly excited Rydberg states with large v _f are determined. The results of calculations testify that the probabilities of all σ transitions n _i ¹ S ₀ → n _f ¹ P ₁ and π transitions to the states with n _f > n _i /2 are decreased with increasing electric field strength, except for the transition 2¹ S ₀ → 2¹ P ₁, whose probability increases both for σ and for π transitions.     

Doppler three-level (V-scheme) laser without population inversion

The theory of amplification and lasing without population inversion in a three-level medium with inhomogeneous broadening via the formation of an open V configuration is elaborated. The conditions for energy transfer from the infrared into the visible spectral range, i.e., the conditions of up-conversion n _b >n _c >n _a , and the external field required for saturation of the b?a transition are established. Two-photon resonant Raman transitions in ensemble of mobile atoms of a gas-discharge plasma are analyzed. The frequency shift of the probe field spectrum as a whole is shown to be governed by the frequency shift of the pump field multiplied by the ratio of the wave numbers of the probe amplification field and the pump field. The interaction of atoms through Ne transitions with the pump field (λ=1.15 εm, 2p ₄-2s ₂ transition) and the lasing field (λ=0.6328 εm, 3s ₂-2p ₂ transition) with an increase in the lasing frequency by a factor of 1.82 with respect to the absorbed radiation is calculated.     

Evolution of an optically pumped ensemble of cold ground-state atoms in weak light fields

The evolution of multipole moments is analyzed for optically pumped cold ground-state atoms in the limit of low saturation of a closed j₀ → j₁ dipole transition. The longest multipole-moment relaxation times are analyzed as functions of ellipticity and frequency detuning from resonance for transitions with j₀ ? 5. The qualitative difference between the evolution toward steady-state Zeeman sublevel populations and dynamics of transient spontaneous emission is demonstrated for transitions of the following types: j → j?1, j → j with integer j, j → j with half-integer j, and j → j + 1.     

Theoretical Analysis of the Fluorescence Spectra of 7-Azaindole and Its Tautomer

The electronic—vibrational fluorescence spectra of the first, S₀ → ¹L_b, and second, S₀ → ¹L_a, electronic transitions of 7-azaindole and its tautomer for an isolated state have been calculated. Specific features of structural changes in 7-azaindole and its tautomer upon electronic excitation are determined. Vibrational spectra are assigned for the ground state, and the vibrational structure of fluorescence spectra is interpreted. It is shown that the intensity redistribution between the 6a and 6b oscillations, which is observed in the fluorescence spectrum of the S₀ → ¹L_b transition in 7-azaindole, can be explained as a result of intensity borrowing (according to the Herzberg—Teller mechanism) from the ¹L_a state.     

Specific features of the two-photon absorption of cationic symmetric polymethine dyes

The two-photon absorption of a number of cationic symmetric polymethine dyes based on 3H-indolium and benzothiazolium is experimentally studied upon excitation by nanosecond radiation from a Nd:YAG laser (1064 nm, 12 ns). The two-photon absorption cross section of dye molecules is determined by the two-quantum standard method. The influence of the spectral-luminescent properties and structure of the polymethine dyes on the two-photon absorption cross section is discussed. It is shown that, upon excitation in the range of the long-wavelength band of the dyes studied (the S ₀ → S ₁ transition), the maximum of their two-photon absorption is blue shifted. The reasons for a considerable increase in the two-photon absorption of symmetric polymethine dyes upon their excitation in the range of the S ₂ state are discussed. Using the data of quantum-chemical calculations, it is shown that, along with changes in the selection rules for two-photon transitions, this increase is connected with an increase in the size of the delocalized π electron cloud of HOMOs involved in the S ₀ → S ₂ transition.     

Description of composite systems in the spectral integration technique: The gauge invariance and analyticity constraints for the radiative decay amplitudes

The constraints following from gauge invariance and analyticity are considered for the amplitudes of radiative transitions of composite systems, when composite systems are treated in terms of spectral integrals. We discuss gauge-invariant amplitudes for the transitions S → γS and V → γS, with scalar S and vector V mesons being two-particle composite systems of scalar (or pseudoscalar) constituents, and we demonstrate the mechanism of cancellation of false kinematical singularities. Furthermore, we explain how to generalize this consideration for quark-antiquark systems, in particular, for the reaction φ(1020) → γf₀(980). Here, we also consider in more detail the quark-model nonrelativistic approach for this reaction.     

Quark diagram analysis of bottom meson decays emitting pseudoscalar and vector mesons

This paper presents the two body weak nonleptonic decays of B mesons emitting pseudoscalar (P) and vector (V) mesons within the framework of the diagrammatic approache at flavor SU(3) symmetry level. Using the decay amplitudes, we are able to relate the branching fractions of B → PV decays induced by both b → c and b → u transitions, which are found to be well consistent with the measured data. We also make predictions for some decays, which can be tested in future experiments.     

Fine-structure phosphorescence and radiative deactivation of the lowest triplet states in the most toxic dioxins

The transition dipole moments for the transition T₁(ππ*) → S₀ to vibrational energy levels of the nontotally symmetric vibrational modes of 2,3,7,8-tetrachloro-and 1,2,3,7,8-pentachlorodibenzo-p-dioxins are calculated. The interpretation of the fine-structure phosphorescence spectrum of the first of these compounds is refined, and the radiative deactivation rate constants for the s sublevels of the lowest triplet state T₁ are estimated. For a number of polychlorinated compounds, the effect of chlorine atoms occupying the α and β positions in a molecule on the T^s → S₀ transition dipole moments is discussed.     

Multicomponent <Emphasis Type="Italic">n</Emphasis>-(Bi,Sb)<Subscript>2</Subscript>(Te,Se,S)<Subscript>3</Subscript> solid solutions with different atomic substitutions in the Bi and Te sublattices

The thermoelectric properties of n-Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions are studied in the temperature range 300–550 K. It is shown that an increase in the parameter β determining the figure-of-merit Z of the material is observed in compositions with the optimally related effective mass of the density of states m/m ₀, the carrier mobility μ₀, and the lattice thermal conductivity κ _L . Within the temperature range 300–350 K, the parameter β and the figure-of-merit Z are found to increase in solid solutions with substitutions in both bismuth telluride sublattices Bi → Sb and Te → Se, S (x = 0.16, y = z = 0.12) for optimum electron concentrations. An increase in the electron concentration and substitutions of atoms only in the tellurium sublattice bring about an increase in the β parameter and the value of Z at higher temperatures. Within the range 350–450 K, the parameters β and Z are observed to increase in a solid solution with a low content of substituted atoms in the tellurium sublattice Te → Se, S for y = z = 0.09 and, at higher temperatures up to 550 K, in compositions with tellurium substituted by selenium only, with increasing content of substituted atoms.     

Energy scan of cross sections for <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>–</Superscript> annihilation into quarkonia and light hadrons in the Belle experiment

The cross sections of the reactions e⁺e^– → ?(nS)π⁺π^? (n = 1, 2,3) and e⁺e^– → h _b (nP)π⁺π^? (n = 1, 2) are measured as a function of the cms collision energy from their thresholds up to 11.02 GeV using the data of the Belle experiment operating at the KEKB e⁺e^– collider. The peaks of the ?(10 860) and ?(11020) resonances are observed in the cross sections with an insignificant contribution of the continuum. The decay ?(11020) → h _b (nP)π⁺π^? is found to fully proceed through intermediate isovector states Z _b (10610) and Z _b (10650).     

A uniform quasi-classical description of radiative transitions for asymmetric rare-gas atom-atom collisions

The uniform quasi-classical approximation [14] is used to describe the optical spectra formed during asymmetric collisions between atoms of rare gases in which one of the atoms is in a metastable state. We consider the reactions He(2¹S) + Ne → He(1¹S) + Ne + ?ω and Ar(³P₂) + He → Ar(¹S) + He + ?ω, in which the optical transition mechanisms are typical of most rare gases. Quasi-molecular terms of excited states and radiative widths calculated in a unified semiempirical approach are used. Spectral characteristics are calculated for thermal collision energies in the entire frequency range, including the center and both wings of the forbidden line. For the blue wing, our results are consistent with the widely used Condon approximation at collision energies E ≥200 cm^?1. At lower collision energies and in the region of the red wing and center of the forbidden line, the spectral distributions that cannot be described in the Condon approximation are reproduced in the uniform quasi-classical approximation. Comparison with quantum-mechanical calculations by the strong-coupling method confirms the high accuracy of the uniform quasi-classical approximation in the entire range of radiation frequencies.     

Faraday effect in alkali-metal vapors in a strong bichromatic field of laser light

Results of a numerical study of the Faraday effect arising upon propagation of the light beams with the frequencies ω _L1 (resonant to the nS _1/2-nP _{1/2, 3/2} transitions) and ω _L2 (resonant to the nP _{1/2, 3/2}-(n+2)S _1/2 transitions) through alkali-metal vapors are presented. Characteristics of the magneto-optical rotation spectra at each of the frequencies are strongly affected by the second intense radiation field resonant to the adjacent transition. When the atoms interact with two strong light waves, resonant to adjacent transitions, and with a magnetic field, the shape of the Faraday rotation spectra depends on the energy shifts of the atomic states that arise due to the dynamic Stark effect and the Zeeman effect (the Paschen-Back or an intermediate-type effect), as well as due to the difference of populations of these states caused by the interaction of the atoms with the fields. The results obtained show that in the frequency selection method, based on the resonance Faraday effect, the frequency of the generated narrow-band beam can be tuned by the intensity of the strong wave, resonant to the transition between the excited states.     

Manifestation of the vibronic analogue of the Fermi resonance in quasi-line spectra of porphyrins: Experiment and theoretical analysis

The quasi-line low-temperature (4.2 K) fluorescence excitation spectra of two porphyrins, meso-tetraazaporphin and meso-tetrapropylporphin introduced into an n-octane matrix are measured in the range of the S ₀ → S ₂ electronic transition. A characteristic feature of these spectra is that a conglomerate of quasi-lines—a structured complex band—is observed instead of one 0–0 quasi-line of the S ₀ → S ₂ transition. In this band, the intensity distributions for the two main types of impurity centers considerably differ from each other. The occurrence of such conglomerates is interpreted as a result of nonadiabatic electronic-vibrational interactions between vibronic S ₂ and S ₁ states (the complex vibronic analogue of the Fermi resonance). The frequencies and intensities of individual transitions determined from the deconvolution of complex conglomerates are used as the initial data for solving the inverse spectroscopic problem: the determination of the unperturbed electronic and vibrational levels of states involved in the resonance and the electronic-vibrational interaction matrix elements between them. This problem is solved with a method developed previously. The energy intervals between the S ₂ and S ₁ electronic levels of the two main types of impurity centers formed by molecules of a given porphyrin in the crystal matrix are found to significantly differ from each other (～100 cm^?1). At the same time, the energies of the unperturbed vibrational states of the S ₁ electronic level partcipating in the resonance are very close to each other for these two types of impurity centers.     

The effects of cup-like and hill-like parabolic confining potentials on photoionization cross section of a donor in a spherical quantum dot

A theoretical investigation of the effects of hill-like and cup-like parabolic confiningelectric potentials on photoionization cross section (PCS) in a spherical quantum dot ispresented. The hill-like and the cup-like parabolic potentials are superimposed on aninfinite spherical square well (ISSW) potential. As the cup-like parabolic potentialintensifies, the peak of the PCS becomes redshifted for the s → ptransition, and becomes blueshifted for the p → d, d → f (andso forth) transitions. The hill-like parabolic potential, on the contrary, blueshiftspeaks of the PCS for s →p transitions, while it redshifts those oftransitions between higher states as it intensifies. Consequently, the two potentialsdiscriminate between transitions involving the ground state and those involving higherstates.     

Excitation of resonance lines of the cadmium ion by monoenergetic electrons

The excitation of resonance lines at 226.5 and 214.4 nm, corresponding to the transitions 226.5 (5p ² P ₁ ^2/0 →5s ² S _1/2) and 5p ² P ₃ ^2/0 → 5s ² S _1/2, respectively, in the Cd⁺ ion upon collisions with monoenergetic electrons with an energy in the range of 4–130 eV is studied with high precision by a spectroscopic method in crossing beams. It is found that the dependence of the effective excitation cross sections of the resonance doublet components on the energy of the electrons has a distinct resonance structure. It is shown that the dominant mechanism responsible for this structure is the capture of an incident electron by a Cd⁺ ion with the simultaneous excitation of an electron from the subvalence 4d ¹⁰ shell to the autoionizing states of the Cd atom with their subsequent decay (directly or via cascade transitions) to resonance levels of the ion. The results obtained are compared with data from other experiments and with the results of the R-matrix strong-coupling calculation of 15 states and of semiempirical calculation using the Van Regemorter formula.     

The shape of saturated absorption resonance in atoms with degenerate levels and light pressure effect

Anomalous behavior of the shape of saturated absorption resonance on the transition 1s₅→ 2p₈ (J=2→J=2) in the Ne atom is experimentally observed. The shape of the saturation resonance on transitions with degenerate excited states of atoms is analyzed numerically and the reasons for the anomalous behavior of the resonance shape and the formation of its doublet spectral structure are established. The effect of the resonance light pressure on the amplitude and frequency properties of resonance is investigated. It is shown that the asymmetry of the doublet splitting of the resonance is associated with the effect of resonance light pressure.     

Measurement of the Lamb shift 42S1/2-42P1/2 of the helium ion

Helium ions were produced in then=4 states by electron collisions with ground state atoms, resulting in simultaneous ionization and excitation. Dipole transitions between the Zeeman levels of the states 4² S _1/2 and 4² P _1/2 were induced by a microwave electric field. The intensity of the emitted Fowlerα line 4686 Å, corresponding to transitions from then=4 to then=3 states was then reduced by about 3%. From the measurements, a value of the Lamb shiftδ=1751±25 MHz was obtained, compared with the theoretical valueδ=1768.23±0.55 MHz, and the results ofLea, Leventhal andLamb ofδ=1765±20 MHz.     

Isotope shifts of the ground state of neon: Refining the measurement results

Abstract—It has been revealed that the published results of measurements of the isotope shift of the ground state of even neon isotopes contain systematic errors. The errors are caused by the use of erroneous data regarding the absolute values of specific mass shifts of excited states and by the measurement errors of the isotope shifts themselves for transitions to the ground state. The isotope shift of the 2p⁵4s[3/2]₁ → 2p⁶(¹S₀) transition has been measured to be 2305 ± 20 MHz, the absolute specific mass shift of the 3p[3/2]₂: (2_р9) level has been determined to be 647 ± 10 MHz, and the isotope shift of the ground state has been found to be–3156 ± 30 MHz.     

Effect of Zeeman Depopulation Pumping on Cycling Atomic Transitions

The results of an investigation of fluorescence signal at 6S_1/2 (F_g = 4) → 6P_3/2 (F_e = 5) transition of D₂ line of atomic Cs vapor versus the magnetic field (up to B = 90 G), directed along the linear polarization of exciting light are presented. The recorded reduction of fluorescence in the magnetic field, which is especially strong at high intensity of laser radiation, is explained by conversion of the Zeeman optical pumping (the alignment) into the depopulation pumping under conditions, when the Zeeman frequency shift of individual transitions between magnetic sublevels exceeds the homogeneous width of transition. In consequence, the cycling hyperfine transition F_g = 4 → F_e = 5 is transformed into an open one.