Atomic Absorption Lines Research Articles

Quadripartite entanglement from two-port resonator with second-order harmonic generation

Quantum entanglement is a crucial resource for performing quantum computing and constructing quantum communication networks. The preparation and manipulation of entangled light field are the basic elements of quantum communication. With the development of science and technology, multicolor multipartite entanglement is becoming a kind of special resource for quantum information, quantum networks, and quantum memory. In this paper, we propose a scheme of generating quadripartite entanglement among four output beams from a two-port frequency doubling resonator, in which a type-II phase matching nonlinear crystal is placed. We make two fundamental-frequency pump beams with the same frequency and vertical polarization pass through the nonlinear crystal to produce two frequency-doubling beams. There is a quadripartite entanglement between the frequency-doubling beams, which are output at two ports of the optical resonator, and the incident fundamental beams. Based on the transmission matrix from the coupled wave equation, the self-consistent equations of the intracavity modes and the corresponding noise properties of the output modes can be obtained. Then, the quadripartite entanglement produced from two second harmonic beams and two reflected fundamental-frequency pump beams, is verified by using the positive partial transposition criterion, in a wide range of pumping power and analysis frequency. The setup proposed in this work is compact and experimentally feasible. It is also convenient to separate the four entangled beams spatially, with different wavelengths and polarizations. When the beam wavelengths are matched with 1560 nm (low loss window of fiber) and 780 nm (atomic absorption line of Rb), this scheme can be more useful in both quantum communication and quantum memory.

Direct observation evidence for the origin of broad emission lines in quasars: Understanding emission via absorption

This year marks the 60^th anniversary of quasar discovery in 1963. The kinematics of gaseous clouds in quasars have been the subject of decades-long debate, focusing on two modelsrotation and blowing-wind. The rotation model, wherein gaseous clouds orbit black holes, is widely accepted by astronomers and frequently used to measure supermassive black hole (SMBH) masses in quasars. Another model is blowing-wind model, in which the gaseous clouds are outflows and in linear motion toward all directions. Our study creatively employs the quasar absorption line technique, utilizing atomic hydrogen Balmer absorption lines for identification, especially during eclipses of inner emitting clouds. The ambiguous presence of hydrogen Balmer absorption lines hints at massive eclipse clouds near central black holes, but detection is hindered by obscuration from dusty tori outside the broad emission line-producing region. We conduct an intensive survey among million quasars in Sloan Digital Sky Survey (SDSS) and acquire a small sample of quasars with hydrogen Balmer absorptions on their spectra. Three quasars exhibit significant variabilities over a decade, contradicting the blowing-wind model, which predicts constant motion along the line of sight with no absorption variabilities. The discovery servers as the direct observation evidence for the rotation model of broad emission lines in quasars. Rotation velocities of eclipse clouds, consistent with expected velocities of emission line clouds, confirm homology between absorption and emission clouds.

Detection of molecular oxygen using nanosecond-laser-induced plasma.

Molecular oxygen (O2) concentration is measured by employing nanosecond laser-induced plasmas (ns-LIP) over a broad temperature spectrum ranging from 300 K to 1000 K, in the presence of an additional oxygen-containing molecule, CO2. Typically, emission spectra emanating from ns-LIP are devoid of molecular information, as the ns-LIP causes the dissociation of molecular species within the plasma. However, atomic oxygen absorption lines that momentarily appear at 777 nm in the broadband emission from the early-stage plasma are determined to be highly sensitive to the O2 mole fraction but negligibly affected by the CO2 mole fraction. The atomic O absorbing the plasma emission originates from the O2 adjacent to the plasma: robust UV radiation from the early-stage plasma selectively dissociates adjacent O2, exhibiting a relatively low photodissociation threshold, thus generating the specific meta-stable oxygen capable of absorbing photons at 777 nm. A theoretical model is introduced, explicating the formation of the meta-stable O atom from adjacent O2. To sustain the UV radiation from the plasma under high-temperature and low-density ambient conditions, a preceding breakdown is triggered by a split laser pulse (532 nm). This breakdown acts as a precursor, seeding electrons to intensify the inverse-Bremsstrahlung photon absorption of the subsequent laser pulse (1064 nm). Techniques such as proper orthogonal decomposition (POD) and support vector regression (SVR) are employed to precisely evaluate the O2 mole fraction (<1% uncertainty), by analyzing the short-lived (<10 ns) O2-indicator depicted in the early-stage plasma.

M67 Blue Stragglers with High-resolution Infrared Spectroscopy

We report on the first detailed infrared chemical analysis of five binary members (S277, S997, S975, S1031, and S1195) in the open cluster M67 (NGC 2682). These stars are located outside (bluer and/or brighter than) the main-sequence turnoff region in M67. High-resolution (R ∼ 45,000) near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope, providing full spectral coverage of the H and K bands. The abundances of C, Na, Mg, Al, Si, S, Ca, Fe, and Ni are measured using neutral atomic absorption lines. We detect v sin i ≥ 25 km s−1 in three of our program stars: S1031, S975, and S1195. We find our derived abundances to be in good agreement with turnoff star abundances, similar to published analyses of blue straggler stars in M67 from optical spectra. Detection of a carbon enhancement or depletion resulting from mass transfer is difficult due to the uncertainties in the carbon abundance and the relatively modest changes that may occur through red giant and asymptotic giant branch evolution.

V838 Mon: A slow waking up of Sleeping Beauty?

Context. V838 Monocerotis is a peculiar binary that underwent an immense stellar explosion in 2002, leaving behind an expanding cool supergiant and a hot B3V companion. Five years after the outburst, the B3V companion disappeared from view, and has not returned to its original state. Aims. We investigate the changes in the light curve and spectral features to explain the behaviour of V838 Mon during the current long-lasting minimum. Methods. A monitoring campaign has been performed over the past 13 years with the Nordic Optical Telescope to obtain optical photometric and spectroscopic data. The datasets are used to analyse the temporal evolution of the spectral features and the spectral energy distribution, and to characterise the object. Results. Our photometric data show a steady brightening in all bands over the past 13 years, which is particularly prominent in the blue. This rise is also reflected in the spectra, showing a gradual relative increase in the continuum flux at shorter wavelengths. In addition, a slow brightening of the Hα emission line starting in 2015 was detected. These changes might imply that the B3V companion is slowly reappearing. During the same time interval, our analysis reveals a considerable change in the observed colours of the object along with a steady decrease in the strength and width of molecular absorption bands in our low-resolution spectra. These changes suggest a rising temperature of the cool supergiant along with a weakening of its wind, most likely combined with a slow recovery of the secondary due to the evaporation of the dust and accretion of the material from the shell in which the hot companion is embedded. From our medium-resolution spectra, we find that the heliocentric radial velocity of the atomic absorption line of Ti I 6556.06 Å has been stable for more than a decade. We propose that Ti I lines are tracing the velocity of the red supergiant in V838 Mon, and do not represent the infalling matter as previously stated.

Photometric and Spectroscopic Study of the EXor-like Eruptive Young Star Gaia19fct

Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined two classes. We present the analyses of light curves, color variations, spectral lines, and CO modeling. The light curves show at least five brightening events since 2015, and the multifilter color evolutions are mostly gray. The gray evolution indicates that bursts are triggered by mechanisms other than extinction. Our near-infrared spectra exhibit both absorption and emission lines and show time variability throughout our observations. We found lower rotational velocity and lower temperature from the near-infrared atomic absorption lines than from the optical lines, suggesting that Gaia19fct has a Keplerian rotating disk. The CO overtone features show a superposition of absorption and emission components, which is unlike other young stellar objects. We modeled the CO lines, and the result suggests that the emission and absorption components are formed in different regions. We found that although Gaia19fct exhibits characteristics of both types of eruptive young stars, FU Orionis–type objects and EX Lupi–type objects, it shows more similarity with EXors in general.

The Effects of Stellar Gravity Darkening on High-resolution Transmission Spectra

Abstract High-resolution transmission spectroscopy is a powerful method for probing the extended atmospheres of short-period exoplanets. With the advancement of ultrastable echelle spectrographs and the advent of 30 m class telescopes on the horizon, even minor observational and physical effects will become important when modeling atmospheric absorption of atomic species. In this work we demonstrate how the nonuniform temperature across the surface of a fast rotating star, i.e., gravity darkening, can affect the observed transmission spectrum in a handful of atomic transitions commonly observed in short-period exoplanet atmospheres. We simulate transits of the ultrahot Jupiters KELT-9 b and HAT-P-70 b but our results are applicable to all short-period gas giants transiting rapidly rotating stars. In general, we find that gravity darkening has a small effect on the average transmission spectrum but can change the shape of the absorption light curve, similar to the effect observed in broadband photometric transits. While the magnitude of gravity-darkening effects are on the same order as the noise in transmission spectra observed with 10 m class telescopes, future high-quality spectroscopic light curves for individual atomic absorption lines collected with 30 m class telescopes will need to account for this effect.

Analysis of the hyperfine splitting spectral structure of rubidium atomic D1 and D2 lines with pressure broadening

A physical model is established to describe the broadening mechanism of rubidium atomic D1 and D2 lines, hence to improve rubidium vapor laser efficiency. Hyperfine energy level structures of rubidium D1 and D2 transitions are analyzed and plotted. Considering the effects of the isotopic frequency shift, the pressure broadening and the hyperfine energy levels splitting, contributions of every hyperfine component to the cross sections are calculated and discussed. The relationship between cross sections and the ratio of helium pressure to ethane is achieved, and the composition of the buffer gas is optimized. The broadening effects of Rb D1 line and D2 line under different buffer gas pressure are also presented. The calculation results have a good agreement with that of experiments, which shows the validity of this model. The simulations data provides a reference for the experiment to further improve the bandwidth matching between alkali atomic D2 absorption line and the diode laser pump source.

The CARMENES search for exoplanets around M dwarfs

Context. M-dwarf spectra are complex and notoriously difficult to model, posing challenges to understanding their photospheric properties and compositions in depth. Vanadium (V) is an iron-group element whose abundance supposedly closely tracks that of iron, but has origins that are not completely understood. Aims. Our aim is to characterize a series of neutral vanadium atomic absorption lines in the 800–910 nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape, which is a result of hyperfine structure (HFS). We investigate the potential and implications of these HFS split lines for abundance analysis of cool stars. Methods. With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we modeled these striking line profiles. We used them to measure V abundances of cool dwarfs. Results. We determined V abundances for 135 early M dwarfs (M0.0 V to M3.5 V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]–[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight (±0.1 dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that neglecting to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with Teff ≲ 5300 K. Conclusions. Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than ~5000 K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy.

The Galactic Chemical Evolution of Chlorine

Abstract We measured 35Cl abundances in 52 M giants with metallicities in the range −0.5 &lt; [Fe/H] &lt; 0.12. Abundances and atmospheric parameters were derived using infrared spectra from CSHELL on the NASA Infrared Telescope Facility and from optical echelle spectra. We measured Cl abundances by fitting a H35Cl molecular feature at 3.6985 μm with synthetic spectra. We also measured the abundances of O, Ca, Ti, and Fe using atomic absorption lines. We find that the [Cl/Fe] ratio for our stars agrees with chemical evolution models of Cl, and the [Cl/Ca] ratio is broadly consistent with the solar ratio over our metallicity range. Both indicate that Cl is primarily made in core-collapse supernovae with some contributions from Type Ia supernovae. We suggest that other potential nucleosynthesis processes, such as the ν-process, are not significant producers of Cl. Finally, we also find our Cl abundances are consistent with H ii and planetary nebular abundances at a given oxygen abundance, although there is scatter in the data.

Observability of ultraviolet Ni lines in the atmosphere of transiting Earth‐like planets

Nitrogen is a biosignature gas that cannot be maintained in its Earth‐like ratio with CO2 under abiotic conditions. It has also been proven to be notoriously hard to detect at optical and infrared wavelengths. Fortunately, the ultraviolet region, which has only recently started being explored for terrestrial exoplanets, may provide new opportunities to characterize exoplanetary atmospheric nitrogen. In this work, the future prospects for detecting atomic nitrogen absorption lines in the transmission spectrum of an Earth‐like planet orbiting in the habitable zone of a Sun‐like star with LUVOIR are explored. Using the nonlocal thermodynamic equilibrium spectral synthesis code Cloudy, we produce a far‐ultraviolet atomic transmission spectrum for an Earth–Sun‐like system and identify several nitrogen features, including both Ni and Nii lines. We calculate the number of transits required for 1σ and 3σ detections of the planetary Ni λ1200 triplet signal with the G120M grating of the LUMOS spectrograph designed for LUVOIR as a function of distance to the system and stellar ultraviolet emission. The minimum number of transit observations necessary for 1σ and 3σ detections of atomic N are 188 and 1,685, respectively, for a system located at a distance of 1 pc with 100 times the solar ultraviolet flux. Given that the orbital period of an Earth–Sun system is 1 year, it is not feasible to detect atomic N in the transmission spectrum for these systems. Future studies in this direction should therefore focus on Earth‐like planets orbiting in the habitable zone of M dwarfs.

Miniature quantum frequency standard based on the phenomenon of coherent population trapping in vapours of 87Rb atoms

We report the results of the development and production of a quantum frequency standard (QFS) based on the coherent population trapping (CPT) resonance observed on the D1 absorption line of 87Rb atoms. The effect of various physical factors on the QFS frequency is studied, and the optimal physical parameters of the device to attain the best frequency stability are determined. The measured relative frequency instability (Allan deviation) is ∼9 × 10−12 for the averaging time of 1 s, 3 ×10−13 for 1000 s, and 1.5 ×10−12 for 24 hours. For a volume of 60 cm3, the power consumption of the entire device is 300 mW. The designed QFS can be used in a new-generation satellite navigation systems with increased accuracy and reliability, as well as for solving a number of other problems of science and technology.

The challenges of Se quantification in bean samples using line and continuum sources atomic absorption spectrometry

This work demonstrates the challenges for selenium (Se) determination in bean samples using high-resolution continuum source Graphite Furnace Atomic Absorption Spectrometry (HR-CS-GF-AAS) and line source Graphite Furnace Atomic Absorption Spectrometry (LS-GF-AAS). Different chemical modifiers were optimized namely; Ir, Ru, and Pd/Mg nitrates. At selenium contents <5 ng g−1, it cannot be quantified accurately. Spectral interferences of the molecular bands of PO and NO as well as the iron lines with Se line at 196.026 were demonstrated. The noticeable low energy of the continuum source of the HR-CS-GF-AAS at 196.026 nm gives high values of the limits of detection and quantification. The Se limits of detection were found to be 24, 33, and 29 ng g−1 for Ir, Ru, and Pd/Mg modifiers, respectively. In situ trapping hydride generation LS-GF-AAS gives better limits of detection and it reached 30 pg g−1 with Ir modifier.

Present-Day Possibilities of High-Resolution Continuous-Source Electrothermal Atomic Absorption Spectrometry

The review covers modern directions of the implementation of high-resolution continuous-source electrothermal atomic absorption spectrometry (HR CS ETAAS) for quantitative analysis. Approaches to the direct analysis of solid samples of various compositions, including determination using aqueous reference solutions, analysis of suspensions and sorbates after sorption separation, use of various modifiers, and optimization of the program of heating graphite furnace are systematized. Restrictions of HR CS ETAAS in the determination of poorly volatile elements are noted, methods for increasing the rate of their atomization in a graphite furnace are described. The potentials of HR CS ETAAS for the simultaneous and consecutive monitoring of atomic lines are investigated. The difference between the simultaneous multielement determination and consecutive determination in one aliquot portion is noted. Restrictions of simultaneous multielement analysis by HR CS ETAAS in the number of elements, their thermochemical properties, and intensities of corresponding absorption lines are described. Possibilities of molecular absorption spectrometry for the determination of analytes whose atomic absorption lines are outside the continuous spectrum range of 190–900 nm are discussed. A promising approach to the determination of sulfur, phosphorus, halogens, and aluminum by absorption lines of diatomic molecules is presented.

Simultaneous Single-Shot Two-Dimensional Imaging of Nanoparticles and Radicals in Turbulent Reactive Flows

Recently, a phase-selective laser-induced breakdown spectroscopy (PS-LIBS) technique has been proposed and developed to diagnose nanoparticles. However, only a few kinds of nanoparticles can generate sufficient strong PS-LIBS signals for single-shot two-dimensional measurement. In this work, we report on the development and validation of a resonance-enhanced PS-LIBS for instantaneous two-dimensional imaging of nanoparticle formation and transport in a turbulent reactive flow. By matching the laser pulse with the absorption line of titanium atoms in the laser-induced nanoplasma, we find that the resonance-enhanced titanium atomic emissions are 1 order of magnitude stronger than the nonresonant spectra ranging from 498 to 502 nm. Based on the spectral characterization, a quantitative relation between the spectra and the particle volume fraction is theoretically established and validated by experiments. Combining the resonance-enhanced PS-LIBS and planar laser-induced fluorescence (PLIF) techniques, instantaneous two-dimensional distributions of the nanoparticle and the hydroxyl radical (OH radical) can be measured in situ in a turbulent reactive flow. The simultaneous measurement demonstrates a strong correlation between the nanoparticle formation and the reactive flow pattern in the turbulent region. The correlation further reveals that the precursor consumption is dominated by the turbulence effect, indicating the precursor chemistry-turbulence coupling.

Narrowing of the Absorption Line of Light Alkali Metal Atoms in an Atmosphere of Heavy Inert Gases at Growing Radiation Intensity

The effect of narrowing of the absorption line of light alkali metal 7Li and 23Na atoms present in an atmosphere of heavy inert gas (xenon) with an increase in the external radiation intensity has been investigated. For 7Li atoms at temperature T = 300 K and buffer gas (Xe) pressure $${{p}_{{{\text{Xe}}}}} = 0.002$$ Torr, the linewidth at half maximum decreases by a factor of 1.20 with an increase in the radiation intensity from 1 µW/cm2 to 2.5 mW/cm2. For 23Na atoms at T = 600 K and $${{p}_{{{\text{Xe}}}}} = 0.01$$ Torr, the linewidth at half maximum decreases by a factor of 1.29 with an increase in the radiation intensity from 1 µW/cm2 to 6 mW/cm2. The effect of field narrowing of the absorption line is due to the following factors. First, the collisional relaxation of the velocities of light resonance particles in an atmosphere of heavy buffer particles is divided into two stages with significantly different durations: relaxation in the velocity direction (fast stage) and relaxation in the velocity magnitude (slow stage). Second, there are no collisional transitions between hyperfine components of the ground state.

Fast inflows as the adjacent fuel of supermassive black hole accretion disks in quasars.

Quasars, which are exceptionally bright objects at the centres (or nuclei) of galaxies, are thought to be produced through the accretion of gas into disks surrounding supermassive black holes1-3. There is observational evidence at galactic and circumnuclear scales4 that gas flows inwards towards accretion disks around black holes, and such aninflow has beenmeasured at the scale of the dusty torus that surrounds the central accretion disk5. At even smaller scales, inflows close to an accretion disk have been suggested to explain the results of recent modelling of the response of gaseous broad emission lines to continuum variations6,7. However, unambiguous observations of inflows that actually reach accretion disks have been elusive. Here we report the detection of redshifted broad absorption lines of hydrogen and helium atoms in a sample of quasars. The lines show broad ranges of Doppler velocities that extend continuously from zero to redshifts as high asabout 5,000 kilometres per second. We interpret this as the inward motion of gases at velocities comparable to freefall speeds close to the black hole, constraining the fastest infalling gas to within 10,000gravitational radii of the black hole (the gravitational radius being the gravitational constant multiplied by the object mass, divided by the speed of light squared). Extensive photoionization modelling yields a characteristic radial distance of the inflow of approximately 1,000 gravitational radii, possibly overlapping withthe outer accretion disk.

Generating conditions of argon laser-sustained plasma by disk, fiber and diode lasers

Laser-sustained plasma (LSP) is a promising method for high-pressure plasma generation that overcomes the problems of arc discharge. Then, the generating conditions of argon LSP were investigated using a kilowatt class disk, fiber and diode lasers. For the disk and fiber lasers, the threshold laser power for LSP generation was found to decrease with pressure. The minimum laser power of the disk and fiber lasers was 1.1 kW at a pressure of 1.5 MPa and 0.45 kW at a pressure of 2.0 MPa. The threshold power of the disk laser was higher than that of the fiber laser. The fiber laser might have a lower threshold because atomic line absorption occurs at 1067 nm and 1068 nm since both absorption coefficients achieved through the Bremsstrahlung process are almost the same. Since LSP could not be generated by a diode laser at a pressure of less than 6.5 MPa, the generating conditions were estimated based on the product of the absorption coefficient of laser intensity. A pressure of more than 8 MPa was found to be necessary for a laser with 1 kW of power, and laser power of more than 109 kW is necessary for a pressure of 0.1 MPa.

Atomic Absorption Line Diagnostics for the Physical Properties of Red Supergiants

Atomic Absorption Line Diagnostics for the Physical Properties of Red Supergiants

The design of modern absolute gravimeters based on atomic interferometers with cold atoms and prospects of their development in Ukraine

Absolute gravimeters on the basis of atomic interferometer with freely falling cold atoms have already demonstrated top-level performance in terms of sensitivity, long-term stability and accuracy which are comparable with the best characteristics of classical ballistic gravimeters, as confirmed in international comparisons. The accuracy of 10 nm·s‑2 is demonstrated not only by stationary laboratory absolute atomic gravimeters, but also by devices intended for field measurements [1]. Atomic gravimeters have a number of potential advantages — the absence of moving parts, a higher sampling rate and they are considered today as a promising area of modern gravimetric technology. In this paper, an overview of publications describing the physi­cal schemes of modern atomic gravimeters is given, the main units of the atomic gravimeter, their purpose and principles of functioning are considered in details. The main attention is paid to laser systems in terms of determining the achievement of necessary conditions for cooling atoms, manipulation of their motion, preparation of quantum states, functioning of the atomic interferometer and detection of the signal. As can be seen from the overview, in modern atomic gravimeters, predominantly semiconductor lasers are used with high, and in some cases, unique technical parameters, which ensure simultaneous achievement of high values of output power, monochromaticity, stability of energy parameters and frequency of radiation, precision control of wavelengths at sufficiently wide range of their values. The creation of such laser systems requires the solution of a number of complex technical problems — the development and creation of effective laser amplification schemes, modulators for the formation of the necessary laser frequencies, and the schemes for locking laser frequencies along the absorption lines of alkaline atoms. The paper also examines the requirements for a highly vacuum system, magnetic shielding schemes, vibration and seismic protection, and discusses the prospects of development of such gravimeters in Ukraine.