Excited Atomic Levels Research Articles

Temperature Sensing via Electromagnetically Induced Transparency Vapor

The behavior of multilevel atomic ensembles (e.g., alkali-metal atoms) can be influenced significantly by the intensity of a driving field (or controlling/coupling field). The phase coherence between two transition pathways driven by a probe light and a driving field can lead to the effect known as electromagnetically induced transparency (EIT). In EIT, the probe light can pass through a three-level alkali-metal atomic vapor without absorption or reflection when two coherent resonances (transition pathways driven by the driving and probe fields) are present and the linewidths of the transparency windows are sufficiently narrow. The optical characteristics of atomic systems can also be affected by the Doppler broadening of the absorption profile in a spectroscope. Our analysis indicates that both broadenings (related to the transitions excited by the driving and probe fields) can be expanded, leading to an increase in the transmittance and reflectance broadenings when a coupling field with adaptive strength is applied; the corresponding temperature would, thus, be implemented and readable. We show that the most suitable preparation for temperature sensing via an EIT vapor is to provide 80 times the spontaneous decay rate (SDR) of the excited atomic levels. This configuration results in reflectance and transmittance values that range between zero and one and cover a temperature range of 0 K to 600 K. As an example, we demonstrate the integration of specialized coating technologies with EIT ensembles for temperature sensing in the range of dozens of kelvins at and above room temperature. A key advantage of this temperature-sensing system is its ability to use adaptive resonant visible light as the probe field. This novel approach may find applications in providing unprecedented levels of precision and control in temperature sensing for coating processes and in the design of other photonic or optical devices. It can also be used to determine the temperature-dependent behavior of the specific heat of alkali-metal solids and gases (including the latent heats of vaporization or sublimation of alkali-metal solids) through the reflection and transmission spectra of the vaporized EIT atomic vapors.

Spontaneous decay of level from spectral theory point of view

In quantum field theory it is believed that the spontaneous decay of excited atomic or molecular level is due to the interaction with continuum of field modes. Besides, the atom makes a transition from upper level to lower one so that the probability to find the atom in the excited state tends to zero. In this paper it will be shown that the mathematical model in single-photon approximation may predict another behavior of this probability generally. Namely, the probability to find the atom in the excited state may tend to a nonzero constant so that the atom is not in the pure state finally. This effect is due to that the spectrum of the complete Hamiltonian is not purely absolutely continuous and has a discrete level outside the continuous part. Namely, we state that in the corresponding invariant subspace, determining the time evolution, the spectrum of the complete Hamiltonian when the field is considered in three dimensions may be not purely absolutely continuous and may have an eigenvalue. The appearance of eigenvalue has a threshold character. If the field is considered in two dimensions the spectrum always has an eigenvalue and the decay is absent.

X-ray detection by direct modulation of losses in a laser cavity

In this work, we experimentally explore the possibility to realize a sensor whose basic building block is a laser cavity that hosts a target crystal for the incident ionizing radiation. Two possible detection mechanisms are considered: a process of coherent scintillation related to the rapid decay via stimulated emission of the excited atomic or molecular levels of the target material and the activation of states that absorb intracavity photons. We use a solid-state laser to study the dynamic response of our prototype sensor and the related intrinsic limitations and demonstrate capability to detect x-ray energy down to 10 GeV.

Vibronic coupling induced by fast Rabi oscillations for kinetic energy control in free atom

Vibronic coupling effects usually manifest themselves in molecules and crystals rather than in unbound atoms. We theoretically demonstrate the existence of vibronic states in a moving two-level atom exposed to a strong electromagnetic (EM) wave. In this case, the Rabi oscillations of the electron density give rise to periodic displacements of the atomic nucleus with the Rabi frequency. The periodic displacements mix the Stark split electron levels and lead to the establishment of a channel for energy transfer in the atomic system. Such a channel paves the way for fast control of the kinetic energy of a free atom with the use of the parameters of an EM wave. Thus, the system kinetic energy can be decreased or increased if the detuning between the laser pulse frequency and the optical transition is positive or negative, respectively. For actual values of the detuning, the pulse duration should be an order of magnitude longer than the lifetime of the excited atomic level in order to complete the energy transfer process.

Spectra of a Rydberg Atom in Crossed Electric and Magnetic Fields

Contemporary spectroscopic studies of astrophysical and laboratory plasmas frequently deal with extremely large values of principle quantum numbers of atomic systems. These atomic states are very sensitive to electric and magnetic fields of the surrounding medium. While interpreting the spectra of such excited atomic systems, one faces the problem of a huge array of radiative transitions between highly excited atomic levels. Moreover, external electric and magnetic fields significantly complicate the problem because of the absence of standard selection rules typical for the spherical quantization. The analytical expression in the parabolic representation for dipole matrix elements obtained by Gordon contains hyper-geometric series and it has a very complex structure. The matrix elements that involve the presence of electric and magnetic fields are calculated while using a representation closely related to the parabolic quantization on two different axes. This matrix element depends in a complex way on the transition probabilities in the parabolic coordinate system (Gordon’s formulas) and the Wigner d-functions. This circumstance leads to even greater computational difficulties. A method of simplification of these complicated expressions for transition probabilities is demonstrated. The semiclassical approximation for coordinate matrix elements (Gulayev) and recurrence properties of the Wigner d-functions are used. The Hnβ line is under consideration. Specific calculations for the transition 10–8 in the case of parallel and perpendicular fields are presented.

Limitations of the semiclassical approach for the problem of two-level atomic ensemble emission in a resonant laser field

Both quantum-electrodynamical (QED) and semiclassical approaches are applied to study the spontaneous emission of an atom or atomic ensemble driven by the strong external laser field. It is demonstrated that the semiclassical approach typically used for analyzing the emission of dressed atomic systems is inconsistent with the QED approach and does not provide a proper description of the emission of two-level atoms in a strong external laser field. That is, aside from a situation where the external radiation is nonresonant, weak enough and does not cause the essential population of the excited atomic level.

Superposition of low-pressure DBD and RF induction discharge for spectroscopic study of dissociative recombination in decaying plasma

The aim of the work was to find the optimal way to set up an experiment for spectroscopic study of the dissociative recombination of molecular ions with electrons in low electron density plasma at low gas pressure. In such an experiment, the influence of inelastic atom–atom collisions on the distribution of the DR flux over the excited atomic levels can be excluded. The first results of an experiment on combining a low-frequency barrier discharge (DBD) in neon at a pressure of less than 1 Torr with a pulsed radio-frequency (RF) induction discharge are presented. To create the plasma, we used DBD in a cylindrical glass tube with an inner diameter of 3.9 cm, which forms the spatial distribution of electron density with a minimum on the axis of the tube. The evolution of such a spatial distribution due to ambipolar diffusion in the initial stage of plasma decay provides an influx of charged particles to the center of the discharge tube, which increases the afterglow duration and helps to overcome the difficulties of detecting weak plasma radiation. The specific features of the DBD also appeared in the ionic composition of the plasma, which contained, in addition to Ne+ and Ne2+, the Ne++ ions, whose recombination with electrons significantly enriched the afterglow spectrum in the short-wavelength region. An RF discharge was used for pulsed heating of electrons in the afterglow. It is shown that, in accordance with the ionic composition, the radiation of a decaying plasma is presented by three groups of spectral lines with characteristic time behavior and the electron temperature dependence. The advantages of the proposed approach for studying the mechanism of dissociative recombination are discussed.

Discrete exited states influence on the harmonics spectrum generated in two-colour laser fields

The contribution of excited discrete atomic levels to the generation of high- and low-order harmonics in the interaction of a single atom with a two-color laser field has been studied for the first time. The studies were carried out for two types of atoms with different symmetry of the ground state wave functions (Ag, Ne) and for a two-color laser field consisting of the linearly polarized fundamental and second harmonics of Ti:Sa laser (ω + 2ω). The angle between the polarization of the ω + 2ω laser field components is varied. A significant effect of the symmetry of populated excited levels on the polarization characteristics of the generated harmonics is shown. A new method of control over the polarization state of the generated radiation is proposed.

Non-Hermitian Magnon-Photon Interference in an Atomic Ensemble.

The interference of photons in a lossy beam splitter (BS) exhibits anticoalescence, which is surprising for bosons. Such a non-Hermitian system involving open quantum dynamics is of particular interest for quantum information processing and metrology. The Hermiticity of photonic devices is generally fixed according to the material, but is controllable at the interface of photons and atomic systems. Here, we demonstrate a tunable non-Hermitian BS for the interference between traveling photonic and localized magnonic modes. The crossover from a Hermitian to a non-Hermitian magnon-photon BS is achieved by controlling the coherent and incoherent interaction mediated by the excited levels of atoms, which is reconfigurable via the detuning of a control laser. A correlated interference pattern between the photons and magnons is demonstrated by such a non-Hermitian BS. Our system has the potential to operate with photons and magnons at the single-quanta level, and it provides a versatile quantum interface for studying the non-Hermitian quantum physics and parity-time symmetry.

Parameters of plasma of high-current nanosecond discharge in air with small admixtures of copper vapor

Introduction . The use of a discharge in air of atmospheric pressure opens the possibility of developing windowless UV lamps that are promising for applications with significant mechanical overloads under various extreme conditions, since they do not contain any quartz elements (windows or bulbs). The output characteristics of such point lamps strongly depend on the plasma parameters of the nanosecond discharge with small admixtures of the vapor metal from which the electrodes are made. At present, there are no data on the parameters of air plasma with small admixtures of copper vapor under the operating conditions of a point lamp, which inhibits the establishment of mechanisms for populating the excited levels of atoms and copper ions in such a plasma. This in turn inhibits the long-range optimization of the output characteristics of such point sources of UV radiation. Purpose . The purpose of the study was to determine the emission characteristics in the spectral range of 200-250 nm of the plasma of high-current nanosecond discharge, between copper electrodes in air at atmospheric pressure under conditions of strong overstress of the discharge gap and to carry out a numerical simulation of the parameters of the plasma of air with small copper impurities under conditions close to those realized in the experiment. Methods . The nanosecond discharge in air of atmospheric pressure between copper electrodes was ignited. The distance between the copper electrodes was 1 mm, which led to the ignition at atmospheric pressure air of a point diffuse discharge of a spherical shape with a diameter of 1 mm. The standard program was used to solve the Boltzmann kinetic equation for the electron energy distribution function (EEDF) for modeling air plasma atmospheric pressure parameters with small copper vapor admixtures, since under the experimental conditions the maximum value of the E/P parameter reached about 530 V cm -1 torr -1 , which is less than the critical value of E/P for nitrogen according to the local electron runaway criterion – 590 V cm -1 torr -1 . Results . Numerical simulation of the plasma parameters established that for the range of reduced electric field strength 610 Td-810 Td, at which experimental studies of the characteristics of a point nanosecond discharge were carried out, mean electron energies varied within the range of 12.2 -15.6 eV; the value of the electron concentration was 10.7·10 21 m -3 – 8.7 ·10 21 m -3 at a current density of 765 · 10 6 A / m 2 on the surface of the copper electrode. The excitation constants of the 2 P 3/2, 1/2 , 2 D 3/2 , 2 D 5/2 , 4 F 7/2 , - states of the copper atom and its ionization were in the range (7.3 – 8.5) 10 -13 m 3 /c, ( 0.29 - 0.28) 10 -13 m 3 /c, ( 0.22 - 0.22) 10 -13 m 3 /c, (0.19 – 0.22) 10 -15 m 3 /c and (0.33 -0.45) 10 -13 m 3 /c,, respectively. The maximum excitation rate constant for nitrogen molecules was for the sum of the singlet states: they were (1.4 10 -14 ) m 3 / s for an electric field strength of 810 Td. The specific losses of the discharge power in the plasma on inelastic collisions of electrons with the components of the gas mixture were maximal for nitrogen molecules and reached 32% for excitation of the sum of singlet nitrogen states. Conclusion . Radiation of the plasma is concentrated in a narrow spectral interval of 200-250 nm, is promising for use as a point UV lamp; the spectral lines 248.9 and 254.4 nm Cu II are promising for estimating the electron temperature in a plasma. Mean electron energy, electron mobility, specific electric power losses and the rate constants of elastic and inelastic scattering of electrons by copper, argon and carbon dioxide, oxygen and nitrogen molecules, the ratio of which was 3: 7.098: 0.266: 159.157: 593.438, depending on the magnitude of the reduced electric field (ratio of the electric field strength (E) to the total concentration of atoms and gas molecules (N)). The range of changes in the parameter E / N = 1-1300 Td (1 ∙10 -17 - 1 ∙ 10 -15 V ∙ cm 2 ) and included the values of the parameter E / N, which were realized in the experiment (610-810) Td.

Dark and bright-state polaritons in triple-Λ EIT system

Properties of polaritons in triple-Λ EIT system are investigated using Sawada-Brout-Chong method. The role of dark and bright-state polaritons in the dynamics of the system is studied in detail by including the decay of excited atomic levels. Time evolution of entanglement of single and three-photon EIT modes within the system is investigated to explain this study.

Spectroscopy of He–Ne afterglow plasma

The afterglow of pulsed low-current discharge in a He–Ne mixture is spectroscopically studied under conditions of competition between the processes of Ne2+ and HeNe+ dissociative recombination with electrons, which are the sources of population of excited levels of neon atoms. The behavior of neon spectral lines in the wavelength range of 350–850 nm corresponding to the transitions from the levels of neon atoms of the 2p53p, 2p53d, 2p54p, 2p54d, 2p55s, 2p55d, 2p56s configurations are studied by the multichannel photoncounting method at electron density ne < 1011 cm–3 and helium and neon pressures PHe = 38 Torr and PNe ≈ 10-5pHe Distributions of recombination fluxes and population over excited states of the neon atom formed in the afterglow by homo- and heteronuclear ions are found. The data obtained show that vibrationally excited molecular ions make no noticeable contribution to the spectrum of decaying He–Ne plasma.

Resonance fluorescence in the resolvent-operator formalism

The Mollow spectrum for the light scattered by a driven two-level atom is derived in the resolvent operator formalism. The derivation is based on the construction of a master equation from the resolvent operator of the atom-field system. We show that the natural linewidth of the excited atomic level remains essentially unmodified, to a very good level of approximation, even in the strong-field regime, where Rabi flopping becomes relevant inside the self-energy loop that yields the linewidth. This ensures that the obtained master equation and the spectrum derived matches that of Mollow.

Characterization of an Atmospheric-Pressure Argon Plasma Generated by 915 MHz Microwaves Using Optical Emission Spectroscopy

The paper presents the investigations of an atmospheric-pressure argon plasma generated at 915 MHz microwaves using the optical emission spectroscopy (OES). The 915 MHz microwave plasma was inducted and sustained in a waveguide-supplied coaxial-line-based nozzleless microwave plasma source. The aim of presented investigations was to estimate parameters of the generated plasma, that is, excitation temperature of electrons Texc, temperature of plasma gas Tg, and concentration of electrons ne. Assuming that excited levels of argon atoms are in local thermodynamic equilibrium, Boltzmann method allowed in determining the Texc temperature in the range of 8100–11000 K. The temperature of plasma gas Tg was estimated by comparing the simulated spectra of the OH radical to the measured one in LIFBASE program. The obtained Tg temperature ranged in 1200–2800 K. Using a method based on Stark broadening of the Hβ line, the concentration of electrons ne was determined in the range from 1.4 × 1015 to 1.7 × 1015 cm−3, depending on the power absorbed by the microwave plasma.

Collision-induced stimulated photon echo on the broad spectral line

The collision-induced stimulated photon echo formed on the broad spectral line on the transition with the angular momentum change is studied theoretically. The dependencies of the echo intensity on the areas of exciting pulses and on the strength of the external magnetic field under the conditions of experiments in ytterbium (174Yb) vapor are obtained. The ways to measure orientation and alignment relaxation rates of the excited atomic level are discussed.

Superluminal light propagation via quantum interference in decay channels

We examine the propagation of a weak probe light through a coherently driven $Y$-type system. Under the condition that the excited atomic levels decay via same vacuum modes, the effects of quantum interference in decay channels are considered. It is found that the interference in decay channels results in a lossless anomalous dispersion between two gain peaks. We demonstrate that the probe pulse propagation can in principle be switched from subluminal to superluminal due to the decay-induced interference. We also show that the system exhibits a high index of refraction with negligible absorption for the driving fields. A dressed-state picture of the atom-light interaction is described to explain the numerical results.

Developments for resonance ionization laser spectroscopy of the heaviest elements at SHIP

The experimental determination of atomic levels and the first ionization potential of the heaviest elements (Z⩾100) is key to challenge theoretical predictions and to reveal changes in the atomic shell structure. These elements are only artificially produced in complete-fusion evaporation reactions at on-line facilities such as the GSI in Darmstadt at a rate of, at most, a few atoms per second. Hence, highly sensitive spectroscopic methods are required. Laser spectroscopy is one of the most powerful and valuable tools to investigate atomic properties. In combination with a buffer-gas filled stopping cell, the Radiation Detected Resonance Ionization Spectroscopy (RADRIS) technique provides the highest sensitivity for laser spectroscopy on the heaviest elements. The RADRIS setup, as well as the measurement procedure, have been optimized and characterized using the α-emitter 155Yb in on-line conditions, resulting in an overall efficiency well above 1%. This paves the way for a successful search of excited atomic levels in nobelium and heavier elements.

Interaction of near-IR laser radiation with plasma of a continuous optical discharge

The interaction of 1.07-μm laser radiation with plasma of a continuous optical discharge (COD) in xenon and argon at a pressure of p = 3–25 bar and temperature of T = 15 kK has been studied. The threshold power required to sustain COD is found to decrease with increasing gas pressure to P t 20 bar and to P t 15 bar. This effect is explained by an increase in the coefficient of laser radiation absorption to 20−25 cm–1 in Xe and 1−2 cm–1 in Ar due to electronic transitions between the broadened excited atomic levels. The COD characteristics also depend on the laser beam refraction in plasma. This effect can be partially compensated by a tighter focusing of the laser beam. COD is applied as a broadband light source with a high spectral brightness.

Model for describing non-equilibrium helium plasma energy level population

A new method for calculating the population of excited levels of helium atoms and ions is suggested. The method is based on direct solution of a system of balance equations for all energy levels for which it was possible to obtain process speed constants. The equations include terms for the processes of particle loss and income by excitation and deexcitation, ionization and recombination as well as losses due to diffusion and radiation. The challenge of solution of such large system is also discussed.

Effect of trapping of resonance radiation in a free-burning Ar arc

A modified method for the solution of the Holstein-Biberman transport equation is proposed for cylindrical geometry, arbitrary absorption coefficient accounting for plasma inhomogeneity and a Lorentz spectral lineshape. The method is applied to the plasma generated by a free-burning arc in argon at atmospheric pressure in order to study the effect of trapping of resonance radiation on the population of the resonance state Ar(1s4). The results obtained are compared with those of a self-consistent nonequilibrium model of the arc including excited atomic levels. They show an enhanced (compared to the results of the nonequilibrium model) population of the resonance state outside of the arc core as an effect of the trapping of resonance radiation and almost negligible collisional de-excitation. In the arc core, the effect is negligible so that the calculated population of the Ar(1s4) state confirms the results obtained with the nonequilibrium model.