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Open quantum systems can be systematically controlled by making changes to their environment. A well-known example is the spontaneous radiative decay of an electronically excited emitter, such as an atom or a molecule, which is significantly influenced by the feedback from the emitter’s environment, for example, by the presence of reflecting surfaces. A prerequisite for a deliberate control of an open quantum system is to reveal the physical mechanisms that determine its state. Here, we investigate the Bose-Einstein condensation of a photonic Bose gas in an environment with controlled dissipation and feedback. Our measurements offer a highly systematic picture of Bose-Einstein condensation under non-equilibrium conditions. We show that by adjusting their frequency Bose-Einstein condensates naturally try to avoid particle loss and destructive interference in their environment. In this way our experiments reveal physical mechanisms involved in the formation of a Bose-Einstein condensate, which typically remain hidden when the system is close to thermal equilibrium., Non-equilibrium Bose-Einstein condensates exist in different systems like polaritons, photons. Here the authors demonstrate photonic BECs in an excited or a non-equilibrium state and explore the flow of the photons coupled to the interferometer in order to minimize the loss.

By coupling a newly developed quantum-electronic-state-selected supersonically cooled vanadium cation (V+) beam source with a double quadrupole-double octopole (DQDO) ion-molecule reaction apparatus, we have investigated detailed absolute integral cross sections (σ's) for the reactions, V+[a5DJ (J = 0, 2), a5FJ (J = 1, 2), and a3FJ (J = 2, 3)] + CH4, covering the center-of-mass collision energy range of Ecm = 0.1-10.0 eV. Three product channels, VH+ + CH3, VCH2+ + H2, and VCH3+ + H, are unambiguously identified based on Ecm-threshold measurements. No J-dependences for the σ curves (σ versus Ecm plots) of individual electronic states are discernible, which may indicate that the spin-orbit coupling is weak and has little effect on chemical reactivity. For all three product channels, the maximum σ values for the triplet a3FJ state [σ(a3FJ)] are found to be more than ten times larger than those for the quintet σ(a5DJ) and σ(a5FJ) states, showing that a reaction mechanism favoring the conservation of total electron spin. Without performing a detailed theoretical study, we have tentatively interpreted that a weak quintet-to-triplet spin crossing is operative for the activation reaction. The σ(a5D0, a5F1, and a3F2) measurements for the VH+, VCH2+, and VCH3+ product ion channels along with accounting of the kinetic energy distribution due to the thermal broadening effect for CH4 have allowed the determination of the 0 K bond dissociation energies: D0(V+-H) = 2.02 (0.05) eV, D0(V+-CH2) = 3.40 (0.07) eV, and D0(V+-CH3) = 2.07 (0.09) eV. Detailed branching ratios of product ion channels for the titled reaction have also been reported. Excellent simulations of the σ curves obtained previously for V+ generated by surface ionization at 1800-2200 K can be achieved by the linear combination of the σ(a5DJ, a5FJ, and a3FJ) curves weighted by the corresponding Boltzmann populations of the electronic states. In addition to serving as a strong validation of the thermal equilibrium assumption for the populations of the V+ electronic states in the hot filament ionization source, the agreement between these results also confirmed that the V+(a5DJ, a5FJ, and a3FJ) states prepared in this experiment are in single spin-orbit states with 100% purity.

We perform detailed variability analysis of two-dimensional viscous, radiation hydrodynamic numerical simulations of Shakura-Sunyaev thin disks around a stellar mass black hole. Disk models are initialized on both the gas-, as well as radiation-, pressure-dominated branches of the thermal equilibrium curve, with mass accretion rates spanning the range from $\dot{M} = 0.01 L_\mathrm{Edd}/c^2$ to $10 L_\mathrm{Edd}/c^2$. An analysis of temporal variations of the numerically simulated disk reveals multiple robust, coherent oscillations. Considering the local mass flux variability, we find an oscillation occurring at the maximum radial epicyclic frequency, $3.5\times 10^{-3}\,t_\mathrm{g}^{-1}$, a possible signature of a trapped fundamental ${\it g}$-mode. Although present in each of our simulated models, the trapped ${\it g}$-mode feature is most prominent in the gas-pressure-dominated case. The total pressure fluctuations in the disk suggest strong evidence for standing-wave ${\it p}$-modes, some trapped in the inner disk close to the ISCO, others present in the middle/outer parts of the disk. Knowing that the trapped ${\it g}$-mode frequency and maximum radial epicyclic frequency differ by only $0.01\%$ in the case of a non-rotating black hole, we simulated an additional initially gas-pressure-dominated disk with a dimensionless black hole spin parameter $a_* = 0.5$. The oscillation frequency in the spinning black hole case confirms that this oscillation is indeed a trapped ${\it g}$-mode. All the numerical models we report here also show a set of high frequency oscillations at the vertical epicyclic and breathing mode frequencies. The vertical oscillations show a 3:2 frequency ratio with oscillations occurring approximately at the radial epicyclic frequency, which could be of astrophysical importance in observed twin peak, high-frequency quasi-periodic oscillations.

This work reassesses previous results and generalizes the expression for the low-frequency spectrum of magnetic fields fluctuations in a thermal plasma, that was previously obtained within the framework of the fluctuation-dissipation theorem. The new approach presented here is able to avoid any approximation yielding a unique expression that covers both the low- and high-frequency spectrum, without the need of procedures to smooth the junction between the two limit frequency regions formerly used. Also, the simultaneous dependence of this intensity on the plasma and on the collisional frequencies is discussed. Finally, the total emitted plasma energy is compared to the Stefan-Boltzmann law of a pure black-body.

Here a strategy was proposed to realize the thermal enhancement of the green luminescence of Tb3+ ion through ground state thermal population. The 5D4-7F5 emission line of Tb3+ ion was observed under the excitation of a commonly used 405 nm laser diode for the first time, to the best of our knowledge. Its intensity was found to increase by ten times upon increasing the temperature from 343 to 783 K. Moreover, this change law was in good accordance with the Boltzmann distribution. It was confirmed that the thermal population of the 7F5 state at the expense of the depopulation of the 7F6 ground state, namely the ground state thermal equilibrium, should be responsible for this uncommon phenomenon. For comparison, the Xe lamp was also used to directly excite the 7F6 -5D3 absorption line of Tb3+ ion. In this case, the 5D4-7F5 emission line of Tb3+ ion was also observed. Different from the former case, this line decreased monotonously upon increasing the temperature over the experimental range. The reason for this change law was also discussed.

Collisional relaxation of high-energy primary electrons (PEs) and generation of secondary electrons (SEs) in a metal are simulated self-consistently by the quantum Boltzmann equation taking into account dynamic screening. An efficient scheme to evaluate the multi-dimensional integral in the collision term is introduced, which enables one to compute time evolutions of nonequilibrium energy distribution functions over an energy range up to a few keV until the whole system reaches thermal equilibrium. Numerical results reveal that rapid energy loss of PEs by plasmon excitation occurs in an early stage, followed by a cascade excitation of SEs near the Fermi level. The overall energy distribution eventually converges to the equilibrium Fermi distribution of partially degenerate electron gas, corroborating the quantum-mechanical H-theorem; time evolutions of the corresponding nonequilibrium entropies are also simulated. The electron temperature and total number of SEs in the final state are consistent with thermodynamic values predicted from the initial energy density of PEs. The number of SEs excited during an early stage (initial 10 fs) turns out smaller for higher PE energies; this feature would bear relevance to an estimation of transient radiation damage in a metallic sample irradiated by an intense femtosecond x-ray laser pulse.

We study collisional rethermalization in ultracold dipolar thermal gases, made intricate by their anisotropic differential cross sections. Theoretical methods are provided to derive the number of collisions per rethermalization, which for dipolar gases, is highly dependent on the dipole alignment axis. These methods are formulated to be easily applied in experimental contexts, even reducing to analytic expressions if the route to thermal equilibrium is governed by short-time dynamics. In the analytic case, collisional rethermalization is fully characterized by the dipole magnitude and orientation, scattering length, and thermalization geometry. These models compare favorably to Monte Carlo simulations, and are shown to model well a recent experimental result on the rethermalization of polar molecular samples., Comment: 11 pages, 9 figures

In the present work, laser-induced plasma (LIP) of Mo is studied using both time and space resolved laser-induced breakdown spectroscopy (LIBS) in air as a function of incident laser energy. For this a second harmonic Q-switched Nd:YAG laser having pulse width of 7 ns and repetition rate of 1 Hz is used. The Boltzmann plot method is employed to estimate the plasma temperature of LIP using MoI and MoII lines separately. The stark-broadened profile of MoI-313.2 nm is exploited to measure the electron density. The temporal study in the time delay range of 0.5–5.0 μs shows that both the parameters, decay with the increase in delay time but increases with the increase in laser energy. It is observed that the plasma temperature estimated for MoII lines is higher than that of the MoI lines during the initial stage of plasma formation, delay time of 0.5–1.0 μs, but at a later time scale, both these species are found to possess nearly the same values of the temperature, indicating the coexistence of thermal equilibrium among the Mo atoms and ions in LIP. Therefore, in the second part of the experiment, time-integrated spatial evolution of the LIP of Mo is studied at a fixed delay of 2 μs as a function of axial distance normal to the target. It is found that emission intensity (MoI and MoII both), plasma temperature, and electron density initially increase with the increase in distance from the target, attains maximum value and then falls down. The Mc-Whirter criteria is applied to test the validity of local thermodynamic equilibrium (LTE). The relaxation time and diffusion length are estimated in time and space resolved studies respectively to take care of the transient and inhomogeneous nature of the LIP. The optical thin condition of LIP is verified by employing the branching ratio method. From these studies, a suitable spatio-temporal is identified where the LTE and optically thin plasma condition hold along with a high signal to noise ratio.

With the downscaled device size, electrons in semiconductor electronics are often electrically driven out-of-thermal-equilibrium with hosting lattices for their functionalities. The thereby electrothermal Joule heating to the lattices can be visualized directly by the noncontact infrared radiation thermometry with the hypothetic Planck distribution at a single characteristic temperature. We report here that the infrared emission spectrum from electrically biased GaAs devices deviates obviously from Planck distribution, due to the additional contribution from non-equilibrium hot electrons whose effective temperature reaches much higher than that of the lattice (T e >T l ). The evanescent infrared emission from these hot electrons is out-coupled by a near-field metamaterial grating and is hence made significant to the total far-field emission spectrum. Resonant emission peak has also been observed when the electron hotspots are managed to overlap spatially with the optical hotspots at the grating resonance. Our work opens a new direction to study nonequilibrium dynamics with (non-Planckian) infrared emission spectroscopy and provides important implications into the microscopic energy dissipation and heat management in nanoelectronics.

We studied a single atom trapped in an optical tweezer interacting with a thermal bath of ultracold atoms of a different species. Because of the collisions between the trapped atom and the bath atoms, the trapped atom undergoes changes in its vibrational states occupation to reach thermal equilibrium with the bath. By using Monte Carlo simulations, we characterized the single atom’s thermalization process, and we studied how this can be used for cooling. Our simulations demonstrate that, within known experimental limitations, it is feasible to cool a trapped single atom with a thermal bath.

In this paper, the study of a spectroscope’s window is designed for an argon gas plasma discharge. The discharge channel has a diameter of 10 mm and length 60 mm. We focus also on both the electron transition from atoms into ions of argon and defining the electron’s measurement electron temperature of the plasma. Its description indicates that the plasma ejection is at good a condition which satisfies the criterion of local thermal equilibrium (L.T.E). Our findings show that the results cope with those ones made by Pingpigret G, et al. in his experiments (2017) [1].

We present systematic ab-initio study on the phonon mode potential as a source of anharmonicity in the crystal. As an example, the transverse optical (TO) mode potential in PbTe has been fitted to density-functional-theory calculated energies of phonons excited with different amplitudes of mode displacements. The corresponding equation of motion has been analytically and numerically solved in 1D and 2D space, respectively. The solution is used for constructing the ensemble of 10,000 systems with potential and kinetic energies selected according to the thermal equilibrium distributions. The velocity auto-correlation function derived from the computed trajectories is then used to calculate the profile of the phonon spectrum for the TO an LA modes at three temperatures of 100, 300, and 600 K. This technique allows for determination of the contribution of non-quadratic potential of the phonon mode to the anharmonicity in the crystal and its effect on the phonon spectrum.

Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.

We extend the description of the nonequilibrium Gross-Pitaevskii equation for microcavity polaritons by including not only the kinetics of the nonresonantly pumped exciton reservoir but also that of the collective excitations---called bogolons---above the condensate. Quasiequilibrium Hartree-Fock-Bogoliubov-Popov self-energies are used to describe the condensate and the bogolons. With nonequilibrium Green functions, the quantum Boltzmann equation of the bogolons in a frame moving with the condensate, together with the coupled Gross-Pitaevskii equation can be derived. The resulting scattering rates contain vertex corrections in form of symmetrized products of the $u$ and $v$ pairing functions of all involved scattering states. Corresponding results have been derived for ultracold atoms by A. Griffin, T. Nikuni, and E. Zaremba [Bose-Condensed Gases at Finite Temperatures, 1st ed. (Cambridge University Press, Cambridge, New York, 2009)] Furthermore, we show that the results of the quantum kinetics also determine the luminescence spectrum including the ghost branch. The kinetics is solved numerically, the resulting condensate, the bogolon distribution, and the luminescence are calculated temporally and spatially resolved after the switch-on of a $\mathit{cw}$ nonresonant pump beam with a Gaussian profile. It is studied in detail to which extent the bogolons approach a local thermal equilibrium.

When particles are held in optical tweezers, we assume that they are in thermal equilibrium. Here we show that this condition only holds for high symmetry cases, e.g. perfectly isotropic particles in unaberrated, linearly polarized Gaussian traps. We show both experimentally and theoretically that when a birefringent microsphere is held in a linearly polarised Gaussian optical trap in vacuum, spontaneous oscillations emerge that grow rapidly in amplitude and become increasingly coherent as the air pressure is reduced. Furthermore, when parametrically driven, these self-sustained oscillators exhibit an ultrahigh quality factor exceeding 200 million, which can be highly sensitive to external perturbations.

We present a quantum thermometry scheme based on a cavity-QED setup, which attains a sensitivity with Heisenberg scaling. A stream of identical two-level systems passes through a thermal bath to be tested. Each system partially thermalizes, carrying information on the temperature of the thermal bath, and it then interacts with a dissipative single-mode cavity. The Heisenberg scaling is attained from the initial coherence of each system. The systems cannot be fully thermalized by the thermal bath. The optimal interaction time between the system and the thermal bath is derived. Direct photon detection is proved to be an optimal measurement when there is no extra thermal bath in the cavity. In the case where there is an extra thermal bath in the cavity independent of the thermal bath to be tested, homodyne detection is the optimal measurement. Moreover, we show that direct photon detection obtains less information in the case where the extra thermal bath in the cavity is in thermal equilibrium with the thermal bath. However, the optimal measurement can utilize the information from the extra thermal bath to improve the estimation precision of the temperature.

When particles are held in optical tweezers, we assume that they are in thermal equilibrium, in which the equipartition of energy determines the position variance of optically trapped spheres. Here we show that this condition only holds for very high symmetry cases, e.g. perfectly isotropic particles in unaberrated, linearly polarized Gaussian traps. We report an experimental observation that when a birefringent microsphere is held in a linearly polarised Gaussian optical trap in vacuum, spontaneous oscillations emerge that grow rapidly in amplitude and become increasingly coherent as the air pressure is reduced. Furthermore, when parametrically driven, these self-sustained oscillators exhibit an ultrahigh mechanical quality factor > 2 x 108, which can be highly sensitive to external purtabations.

Laser-induced tip-enhanced ablation appears to be a promising nanometer-scale sampling approach. Recently we have developed a Near-Field Ablation and Ionization Mass Spectrometer, which is capable of direct ablation and ionization of materials at a scale of tens of nanometers under both nanosecond and femtosecond pulsed lasers. In spite of its great potential as a nanometer-scale sampling source, its underlying mechanism remains to be further explored. To figure out the difference between nanosecond and femtosecond laser-induced tip-enhanced ablations, we developed a three-dimensional theoretical code to explain the ablation phenomena on a Ti-coating sample. With calculated time-evolving and space-distribution features of sample temperature, the simulation justified the time needed to reach electron-lattice thermal equilibrium to be within several picoseconds, and showed that nanosecond laser ablation features much greater thermal effect. We also calculated the theoretical ablated pit profiles and volume after one laser pulse under both lasers. They all fitted well with experimental results. Afterwards, we compared the experimental mass spectra of various salts in the nanosecond and femtosecond laser experiments and studied the roles of properties via chemometrics works. Result again revealed that thermal properties contributed relatively more in the nanosecond laser model. Ionization potential was equally important in both experiments, which met well with the intensity distribution observed in the mass spectra. Moreover, the influences of lattice energy, molar mass and fusion heat were also explained. All these results proved and supported each other, which verifies our study to be reasonable and helps us get a better understanding of this new technique.

We study thermal equilibration in face-centered cubic lattices with harmonic and anharmonic (Lennard-Jones) interactions. Initial conditions are chosen such that the kinetic temperatures, corresponding to three spatial directions, are different. We show that in the anharmonic case the approach to thermal equilibrium has two time scales. The first time scale is the period of atomic vibration. At times of the order of several atomic periods, the approach to equilibrium is accompanied by decaying high frequency oscillations of the temperatures. The oscillations are described analytically using the harmonic approximation. In particular, the characteristic frequencies of the oscillations are calculated. It is shown that the oscillations decay in time more slowly than expected. The second time scale, presented in the anharmonic case only, depends on the initial temperature of the system. Normalizing time by this scale, we obtain numerically a universal curve describing equilibration in the Lennard-Jones crystal over a wide range of temperatures.

It has long been observed that the number of weak lines from many-electron atoms follows a power law distribution of intensity. While computer simulations have reproduced this dependence, its origin has not yet been clarified. Here we report that the combination of two statistical models -- an exponential increase in the level density of many-electron atoms and local thermal equilibrium of the excited state population -- produces a surprisingly simple analytical explanation for this power law dependence. We find that the exponent of the power law is proportional to the electron temperature. This dependence may provide a useful diagnostic tool to extract the temperature of plasmas of complex atoms without the need to assign lines.

International audience; The plasma is generated by a microwave (MW) source inside a conditioned cell with an axial gas injection working at high pressure argon with a small admixture of air. Several characterization methods based on the analysis of the optical emission spectra are employed to determine rotational Trot, vibrational Tvib, excitation Tex and electron Te temperatures along the plasma flame axis. The densities of electrons and oxygen and nitrogen atoms are also determined from spectra analysis for the same plasma axis positions. The rotational and vibrational temperatures are simultaneously estimated using a new method based on the analysis of 3 consecutive band heads of the second positive system (SPS) of molecular nitrogen spectra. This new method, based on pre-calculated synthetic spectra databases, leads to Trot varying from about 2000 to 2500 K along the plasma axis while Tvib are higher (around 5000 K and more). Both temperatures are coherent when determined from N2SPS in the case of two distinct wavelength ranges (around 313 nm and 376 nm). These temperatures are in agreement with Trot determined from comparison between synthetic and experimental OH(A-X) spectra and Tvib determined from the first negative system N2+FNS spectra. The estimated electron temperatures Te are around 2.0 eV while the electron densities are in the range 1015 to 1016cm−3 using a literature method adapted in the present work to air diluted in argon buffer gas. The densities of atomic oxygen are estimated close to 1015 cm−3 and those of nitrogen close to 1016 cm−3 when using an actinometry method assuming a priori known the density of hot buffer argon gas at Trot temperature and also Tex determined using classical Boltzmann plots based on a chosen series of Ar lines. The significant deviations between the different temperatures Trot, Tvib, Tex and Te clearly underline a pronounced non thermal equilibrium of the present MW argon/air plasma. It is also shown an important chemical non-equilibrium since the measured electron, N and O densities are found much higher than the usual equilibrium densities generated by thermal dissociation and recombination processes. This therefore means that the energetic electron impacts play a significant role on the formation of the present non-equilibrium MW plasma.

In this work, the stopping power of a partially ionized helium plasma due to its free and bound electrons is analyzed for an electron temperature and density in which local thermal equilibrium (LTE) or non-local thermal equilibrium (NLTE) regimes can be possible. In particular by means of collisional-radiative models, the average ionization of the plasma as well as the abundances of different helium species (HeI, HeII, and HeIII) are analyzed in both LTE and NLTE thermodynamic states. The influence of this ionization and of the different ion abundances on the stopping power of the helium plasma is shown to be quite significant. Finally, our theoretical model is compared with experimental results on slowing down of swift argon ions in helium plasma.

After achieving significant research results on laser-driven boron fusion, the essential facts are presented how the classical very low-energy gains of the initially known thermal ignition conditions for fusion of hydrogen (H) with the boron isotope 11 (HB11 fusion) were bridged by nine orders of magnitudes in agreement with experiments. This is possible under extreme non-thermal equilibrium conditions for ignition by >10 PW-ps laser pulses of extreme power and nonlinear conditions. This low-temperature clean and low-cost fusion energy generation is in crucial contrast to local thermal equilibrium conditions with the advantage to avoid the difficulties of the usual problems with extremely high temperatures.

The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy, and the influence of the air flow velocity and ambient pressure on these temperatures was investigated. The optical emissions from the plasma were led to an imaging spectroscope through an optical fiber. The temperature was estimated by fitting a theoretically calculated spectrum to that which had been acquired experimentally, formed by nitrogen molecule emission from 372 to 382 nm. The spark-discharge plasma was examined with a flow of ambient air at a discharge energy of 80 mJ. The air flow caused the spark-discharge channel to elongate downstream. At the center of the spark plug gap, the vibrational temperature in the plasma was 4000 K, whereas the rotational temperature was 2000 K. This plasma can be regarded as being in non-thermal equilibrium because the vibrational temperature was higher than the rotational temperature. At a position approximately 3 mm downstream from the spark plug gap, the vibrational and rotational temperatures increased to 4500 and 4000 K, respectively, while approaching each other. Both temperatures reached a maximum value. These results show that the plasma transitions from non-thermal equilibrium to thermal equilibrium as it is elongated by the air flow. Ignition efficiency improvements can be expected if the time required to transition from non-thermal to thermal equilibrium can be shortened.

The characteristics of shock waves in a relativistic plasma in the presence of nonisothermal electrons and nonisothermal negative ions is investigated by deriving the evolution equation in terms of a modified 3D Burgers equation, or trapped 3D Burgers equation. The solution of this equation is examined analytically to study the salient characteristics of shock waves in such plasma. The nonlinear coefficient is found to have the lowest (highest) value when the negative ions move toward thermal equilibrium with a dip-shaped electron distribution (when both electrons and negative ions follow a dip-shaped distribution) for a particular value of relativistic factor, and it remains in an intermediate state when both electrons and negative ions follow a flat-topped distribution. On the other hand, the dissipative coefficient is found to decrease (increase) with increasing relativistic parameter (viscous parameter). A profound effect of the trapped state of both electrons and negative ions and the temperature ratio between positive ions and electrons (negative ions and electrons) on the structure of the shock wave is also seen. However, it has been noticed that the trapped parameter of electrons has a dominating control over the shock potential profile than the trapped parameter of negative ions.

Transition to thermal equilibrium in a uniformly heated two-dimensional harmonic triangular lattice with nearest neighbor interactions is investigated. Initial conditions, typical for molecular dynamics simulations, are considered. Initially, particles have uncorrelated random velocities, corresponding to initial kinetic temperature of the system, and zero displacements. These initial conditions can be realized by heating of the system by an ultrafast laser pulse. In this case, the kinetic temperature of the system oscillates. The oscillations are caused by the redistribution of energy between kinetic and potential parts. At large times, energies equilibrate and temperature tends to the equilibrium value equal to a half of the initial temperature. In our previous works, an integral exactly describing this transient thermal process has been derived. The integrand depends on the dispersion relation for the lattice. The integral contains large parameter, notably time. In the present work, we investigate large time behavior of the kinetic temperature. Simple asymptotic expression for deviation of temperature from the steady state value is derived. The expression contains three harmonics with different frequencies and amplitudes. Group velocities corresponding to these frequencies are equal to zero. Two frequencies are close and therefore beats of kinetic temperature are observed. Amplitude of deviation of temperature from the steady state value decreases inversely proportional to time. It is shown that the asymptotic formula has reasonable accuracy even at small times of order of one period of atomic vibrations.

The lack of spectroscopic measurements for rare CO2 isotopologues was the main motivation of this work. In our present study we report line intensity measurements for 16O12C17O made with a high resolution Fourier transform spectrometer (Bruker IFS-125HR) and a 21 m path cryogenic Herriott cell at Jet Propulsion Laboratory. For this, a 17O-enriched CO2 gas sample was used, which comes as a mixture of primary and several minor CO2 isotopologues. The mole fraction of the 16O12C17O isotopologue in the mixture was determined to be 0.3991 by mass spectrometry from a Stable Isotope Ratio Mass Spectrometer (SIRMS) under stochastic distribution assumption at thermal equilibrium. Since the collisional narrowing effect was observed, the Rautian molecular line shape profile was systematically adopted instead of the Voigt profile. Absolute line positions were also investigated by performing a wavenumber calibration based on CO, HCl and a few well-known 16O12C16O transitions. Finally, around 1000 transitions were studied between 4604 and 5126 cm−1 involving 15 bands of the 16O12C17O isotopologue. All the measured line intensities were renormalized to be the values for 100% pure isotopologue sample. Transition dipole moments and Herman-Wallis factors were derived enabling a global comparison with theoretical calculations and predictions for the 15 bands of the 16O12C17O isotopologue. For the measured line positions, the absolute accuracy is around 2×10−4 cm−1. The accuracies of retrieved line intensities are 2 – 5% for five cold and two hot bands, and 6–30% for eight other weaker hot bands. Results from this work were in a good agreement with HITRAN 2012 for positions, but showed rather significant discrepancies for line intensities. An extensive line list was generated from new experimental measurements in order to improve and validate spectroscopic knowledge of 12C16O17O isotopologue in support of atmospheric remote sensing for the Earth (e.g., OCO-2 mission), Mars and Venus.

We introduce a classical phasor model for the description of multimode photon condensates that thermalize through repeated absorptions and reemissions by dye molecules. Thermal equilibrium is expressed through the fluctuation-dissipation relation that connects the energy damping to spontaneous emission fluctuations. We apply our model to a photonic Josephson junction (two coupled wells) and to one- and two-dimensional arrays of photon condensates. In the limit of zero pumping and cavity losses, we recover the thermal equilibrium result, but in the weakly driven-dissipative case in the canonical regime, we find suppressed density and phase fluctuations with respect to the ideal Bose gas.

The out-of-equilibrium dynamics of electrons and phonons upon laser excitation are often described by the two-temperature model, which assumes that both subsystems are separately in thermal equilibrium. However, recent experiments show that this description is not sufficient to describe the out-of-equilibrium dynamics on ultrashort timescales. Here, we extend and apply a parameter-free microscopic out-of-equilibrium model to describe the ultrafast laser-induced system dynamics of archetypical metallic systems such as gold, aluminum, iron, nickel, and cobalt. We report strong deviations from the two-temperature model on the picosecond timescale for all the materials studied, even for those where the assumption of separate thermal equilibriums seemed less restrictive, like in gold. Furthermore, we demonstrate the importance of the phonon-mode dependent electron-phonon coupling for the relaxation process and reveal the significance of this channel in the lattice equilibration through an indirect coupling between phonons via the electronic system.

The principle of a spectroscopy experiment is described and the various spectroscopic techniques are reviewed, focusing on the information that can be obtained from the shape and intensity of spectra. Expressions for the electron magnetic moment are then presented, and paramagnetic centers are defined, highlighting their diversity. The principle of an EPR experiment is presented, along with a general expression for the absorption signal at thermal equilibrium. Finally, the functioning of a continuous-wave spectrometer is also explained.

We perform a systematic study of the spin polarization of hyperons in heavy-ion collisions using the MUSIC hydrodynamic model with A Multi-Phase Transport (AMPT) pre-equilibrium dynamics. Our model calculations nicely describe the measured collision-energy, centrality, rapidity, and $p_T$ dependence of $\Lambda$ polarization. We also study and predict the global spin polarization of $\Xi^-$ and $\Omega^-$ as a function of collision energy, which provides a baseline for the studies of the magnetic moment, spin, and mass dependence of the spin polarization. For the local spin polarization, we calculate the radial and azimuthal components of the transverse $\Lambda$ polarization and find specific modulating behavior which could reflect the circular vortical structure. However, our model fails to describe the azimuthal-angle dependence of the longitudinal and transverse $\Lambda$ polarization, which indicates that the hydrodynamic framework with the spin Cooper-Frye formula under the assumption of thermal equilibrium of spin degree of freedom needs to be improved., Comment: 12 pages, 12 figures

This work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO2 conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo flux (MCF) simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO2 and O2 at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10−5 to 10−4. These factors are shown to be fundamental to drive contraction in the CO2 microwave discharge.

This work describes the theoretical basis and implementation of the measurement of vibrational (Tvib) and rotational (Trot) temperatures in CH4 by fitting spontaneous Raman scattering spectra in the Pentad region. This method could be applied for thermal equilibrium temperature measurements applications, e.g. in combustion, or vibrational-rotational non-equilibrium applications, such as in plasma chemistry. The method of calculating these temperatures is validated against known temperature thermal equilibrium spectra up to 860 K from published data, giving an estimated relative error of 10%. This demonstrates that both the calculated stick spectrum and the algorithm to determine Tvib and Trot for CH4 is robust to 860 K, but we expect it is valid to 1500 K. Additionally, a number of non-equilibrium spectra generated with a pulsed microwave plasma are fitted to find Tvib and Trot, further demonstrating the applicability of this method in fitting non-equilibrium spectra.

We observe thermalization in the production of a degenerate Fermi gas of polar ${}^{40}\text{K}{}^{87}\text{Rb}$ molecules. By measuring the atom--dimer elastic scattering cross section near the Feshbach resonance, we show that Feshbach molecules rapidly reach thermal equilibrium with both parent atomic species. Equilibrium is essentially maintained through coherent transfer to the ground state. Sub-Poissonian density fluctuations in Feshbach and ground-state molecules are measured, giving an independent characterization of degeneracy and directly probing the molecular Fermi--Dirac distribution., 5 pages, 4 figures; supplementary material (6 pages, 5 figures)

One of the goals of pump/probe spectroscopies is to determine how electrons relax after they have been driven out of equilibrium. It is challenging to determine how close electrons are to a thermal state solely by fitting their distribution to a Fermi-Dirac distribution. Instead, we propose that one compare the effective temperatures of both fermions and collective bosonic modes (derived from the fermions) to determine the distance from a thermal state. Measurements of effective fermionic and bosonic temperatures can be achieved directly via photoemission and nonresonant Raman scattering. Their difference quantifies the distance from thermal equilibrium., 5 pages, 2 figures

In high-resolution core-valence-valence (CVV) Auger electron spectroscopy from the surface of a solid at thermal equilibrium, the main correlation satellite, visible in the case of strong valence-electron correlations, corresponds to a bound state of the two holes in the final state of the CVV Auger process. We discuss the physical significance of this satellite in nonequilibrium pump-probe Auger spectroscopy by numerical analysis of a single-band Hubbard-type model system including core states and a continuum of high-energy scattering states. It turns out that the spectrum of the photo-doped system, due to the increased double occupancy, shares features with the equilibrium spectrum at higher fillings. The pumping of doublons can be watched when working with overlapping pulses at short $\Delta t$. For larger pump-probe delays $\Delta t$ and on the typical femtosecond time scale for electronic relaxation processes, spectra are hardly $\Delta t$-dependent, reflecting the high stability of bound two-hole states for strong Hubbard-$U$. We argue that taking into account the spatial expansion of single-particle orbitals when these are doubly occupied, as described by the dynamical Hubbard model, produces an oscillation of the barycenter of the satellite as a function of $\Delta t$. Pump-probe Auger-electron spectroscopy is thus highly sensitive to dynamical screening of the Coulomb interaction., Comment: 12 pages, 8 figures, v2 as published, title changed

This work presents a method for the determination of atomic transition probability of the emission lines of a given element using the 3D Boltzmann plot method. The method exploits the third (temporal) dimension of a classical 2D Boltzmann plot for the determination of the plasma parameters. As an example and test of the proposed method, we acquired several time-resolved spectra during laser ablation of pure tungsten sample at different energies. The time interval in which the conditions of Local Thermal Equilibrium can be guaranteed was estimated. The results lead to a criterion for the selection of preferred atomic spectral for the measurements of plasma parameters. The effect of self-absorption on the measured transition probabilities is also evaluated and discussed. Fil: Urbina Medina, Ivan Alexander. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentina Fil: Carneiro, D.. Universidade Federal de Roraima; Brasil. Centro Universitário Estácio Da Amazônia; Brasil Fil: Rocha, S.. Universidade Federal de Roraima; Brasil Fil: Farías, Eliel Eleutério. Universidade Federal de Roraima; Brasil Fil: Bredice, Fausto Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentina Fil: Palleschi, Vincenzo. Consiglio Nazionale delle Ricerche; Italia

Bernstein, Greene, and Kruskal (BGK) have developed the theory for one-dimensional stationary nonlinear electrostatic waves in a collisionless plasma [2]. It is a nonlinear kinetic theory formulated in the one-dimensional Vlasov-Poisson framework of equations. If the solution obtained after the BGK analysis is positive, it is a model of a one-dimensional electrostatic coherent structure, usually called a BGK wave. There are certain structures called a phase space holes that develop because of particle trapping in a potential, which is a phase space manifestation of BGK wave. As these structures in phase space have a lower density at the center than the rim, they are “Phase Space Holes”. Depending on which species trapped, phase space holes are further classified as Electron Holes (EHs) and Ion Holes (IHs). Most of the coherent electrostatic structures encountered in space plasmas modeled in terms of these different phase space holes. However, these models assume the space plasma in thermal equilibrium, described by the Maxwell distribution [3]. Several spacecraft data observations reveal that the plasmas in space cannot be assumed to be in thermal equilibrium and these plasmas are best-modelled using generalized Lorentzian distribution or kappa distribution [4]. Hence, a nonlinear kinetic theory for superthermal plasma is an essential component to study the the coherent wave structures in space plasmas. We develop a first ever one-dimensional model of superthermal plasma keeping ions stationary in the electrostatic limit. We have derived the analytical expression for trapped electron density and distribution function of trapped electrons. We find a significant difference in the trapped electron density and distribution function. We find that superthermal plasma is more prone to trapping and as a result, the distribution function in superthermal plasma found steeper and denser than the trapped distribution in thermal plasma. EHs formed in a superthermal plasma are found to have a smaller size than the EHs formed in thermal plasma for same perturbation. The width and amplitude of perturbation play an important role in the development of holes and deciding their characteristics. The analytical expression for width – amplitude inequality relation that decides the stability of EHs has been derived [1]. We have observed that the parametric regime of amplitude and width (perturbation) that supports stable BGK EH solutions in superthermal plasma is less than that of weakly superthermal plasma. It can be observed that both an increase in width and amplitude of wave potential cause an augmentation in the trapping of particles. The amplitude plays a dominant role in the trapping of maximum energetic particles whereas width plays role in deciding the density of particles at the center of the EHs. Thus this theory provides a generalized platform to study BGK modes developed in both thermal and Superthermal background plasma conditions.

Modeling protoplanetary disks and other interstellar media that are not in local thermal equilibrium require the knowledge of rovibrational transition rate coefficients of molecules in collision with helium and hydrogen. We present a computational method based on the numerically exact coupled-channel (CC) method for rotational transitions and a multi-channel distorted-wave Born approximation (MC-DWBA) for vibrational transitions to calculate state-to-state rate coefficients. We apply this method to the astrophysically important case of CO2–He collisions, using newly computed ab initio three-dimensional potential energy surfaces for CO2–He with CO2 distorted along the symmetric and asymmetric stretch (ν1 and ν3) coordinates. It is shown that the MC-DWBA method is almost as accurate as full CC calculations, but more efficient. We also made computations with the more approximate vibrational coupled-channel rotational infinite-order sudden method but found that this method strongly underestimates the vibrationally inelastic collision cross sections and rate coefficients for both CO2 modes considered.

New laboratory measurements of the rate coefficients for the vibrational relaxation of CO(v=1) and CO(v=2) through collisions with CO have been performed. The experimental approach involved creating a temperature-jump in an equilibrium mixture of CO and bath gases by photolyzing a trace amount of O3 in the mixture with a pulsed UV laser. This shifted a small fraction of the CO population to excited vibrational states. Transient diode laser absorption spectroscopy was then used to observe the evolving vibrational state populations as a function of time. Rate coefficients were deduced from the change in collisional relaxation rate with quencher concentration. This work was motivated by the need for a robust non-LTE model to describe Titan's upper atmosphere. Because the gas collision frequencies are not sufficient to reach thermal equilibrium in a non-LTE environment, the distribution of states is not easily predicted. To properly model such a region, all contributing vibrational energy transfer mechanisms must be thoroughly characterized. Despite their importance, the uncertainties associated with several CO quenching rate parameters in the literature are large. In this work, the rate coefficient for CO(v=2) self-quenching was measured to be (2.7 ± 0.6) x 10−12 cm3 molecule−1 s−1and the overall rate coefficient for CO(v=1) self-quenching was measured to be (1.8 ± 0.3) x 10−12 cm3 molecule−1 s−1. Each represents a significant decrease in uncertainty compared with values being used in current Titan non-LTE models.

Parahydrogen-induced polarization (PHIP) is a source of nuclear spin hyperpolarization, and this technique allows for the preparation of biomolecules for in vivo metabolic imaging. PHIP delivers hyperpolarization in the form of proton singlet order to a molecule, but most applications require that a heteronuclear (e.g. 13C or 15N) spin in the molecule is hyperpolarized. Here we present high field pulse methods to manipulate proton singlet order in the [1-13C]fumarate, and in particular to transfer the proton singlet order into 13C magnetization. We exploit adiabatic pulses, i.e., pulses with slowly ramped amplitude, and use constant-adiabaticity variants: the spin Hamiltonian is varied in such a way that the generalized adiabaticity parameter is time-independent. This allows for faster polarization transfer, and we achieve 96.2% transfer efficiency in thermal equilibrium experiments. We demonstrate this in experiments using hyperpolarization, and obtain 6.8% 13C polarization. This work paves the way for efficient hyperpolarization of nuclear spins in a variety of biomolecules, since the high-field pulse sequences allow individual spins to be addressed.

When a plasma irradiates a metal object, a plasma current flows. Plasma currents in the forward and reverse directions, flowing from a powered electrode, for plasma generation, to the metal object, are repeatedly generated. The first plasma current is generated by the applied voltage of the powered electrode. The metal object onto which the plasma flows is charged by the plasma, and the potential of the metal object increases. The potential of the powered electrode follows the time variation of the applied voltage from the AC power supply. Consequently, when the potential time fluctuation of the powered electrode and the potential of the metal object are balanced, a plasma current in the reverse direction is generated. Because the residual charge on the metal object is determined by the dynamic pressure balance due to the potential time fluctuation between the powered electrode and the metal object, the plasma charge flowing in the reverse direction of the electrode can be determined.

International audience; In this work, the sonoluminescence of NH radicals has been evaluated as a new spectroscopic probe for the nonequilibrium plasma produced by multibubble cavitation in liquids. The experiments were performed in aqueous ammonia solutions subjected to power ultrasound at low and high frequencies and under two different rare gases (Ar and Xe). Sonoluminescence (SL) spectroscopy focuses on the emission of the two present systems: NH (A 3 P-X 3 S À) and OH (A 2 S +-X 2 P). Both spectroscopic systems indicate the absence of thermal equilibrium during bubble collapse (T v 4 T r) irrespective of the saturating gas. When Ar is used as the saturating gas, these emissions can be fitted using Specair software and the corresponding rovibronic temperatures are derived. Both species indicate a net increase in vibrational temperatures with the US frequency. In Xe, the SL spectra exhibit OH (C 2 S +-A 2 S +) and NH (c 1 P-a 1 D) emission bands indicating a higher electron temperature compared to Ar. However, in Xe, the SL spectra cannot be satisfactorily fitted because of significant line broadening. The estimation of the intrabubble pressure via SL simulation using Specair software is discussed. Monitoring of the sonochemical activity indicates the formation of H 2 and N 2 H 4 , while no H 2 O 2 accumulates under these conditions. In the presence of Xe, NO is also formed as a sonolysis product. The appearance of new possible reaction pathways under Xe is made possible by the higher plasma electron density and correlates with SL data.

The dissociative chemisorption dynamics of CO on rigid Co(112[combining macron]0) is investigated using a quasi-classical trajectory method on a new global six-dimensional potential energy surface (PES). The PES is fit using a neural network method to represent 24 630 density functional energies in various configurations. The reaction path features deep chemisorption wells and a late barrier for dissociation, agreeing well with previous calculations. The activation energy for dissociation ranges from 0.1 eV at the hollow site to 2.46 eV on the top site, indicating a highly corrugated PES. Effects of the incidence energy of the impinging molecule, its initial orientation, vibrational and rotational excitations, and site specificity are examined. Despite the presence of a low barrier, the initial dissociation probability is very small, even at high incident energies, as a large percentage of trajectories is either trapped or desorbed back to the gas phase. The low reactivity is attributed to inefficient energy transfer into the dissociation reaction coordinate in the chemisorption well where thermal equilibrium is not reached. This system underscores the importance of dynamics in understanding reactions at gas-surface interfaces and in kinetic modeling of catalytic processes.

The mixing of metals and redistribution of the relative abundances of chemical elements in the interstellar medium often takes place on a timescale that exceeds the characteristic timescales for many other processes, such as ionization and the establishment of thermal equilibrium. Under these conditions, different regions of interstellar gas can have different thermal, chemical, and spectral properties. The paper considers the ionization kinetics and thermal regime of interstellar gas with variations in the relative elemental abundances. The thermal properties and observational (spectral) characteristics are most sensitive to variations of the relative abundance of carbon, oxygen, neon, and iron. The dynamic consequences of such variations are considered.

The phenomenological model of non-equilibrium diffusion and release of hydrogen from metals under the effect of electron beam in the sub-threshold region is considered. It is shown that the radiation stimulates the release and diffusion of hydrogen at a rate, significantly exceeds the rate of thermal equilibrium processes in the metals. This can occur in the presence of long-lived, in a time scale of single phonon and electron relaxation, vibrationally excited H-bonds. The proposed model confirms the experimental results previously obtained.

We consider diode-pumped alkali vapour lasers (DPALs), which make it possible to achieve a high output power. Characteristics of such DPALs strongly depend on the physical properties of buffer gases and on structural parameters of a vapour cell. Special attention is paid to a diode-pumped rubidium vapour laser (DPRVL): We have investigated the effect of different conditions on its characteristics. The results show that the linewidth of the D2 line of a DPRVL and the fine-structure mixing rate between two excited energy levels, which are two crucial factors in implementing a high-power DPRVL, increase with the pressure of buffer gases and the temperature of the vapour cell. It is demonstrated that the population ratio of two excited energy levels is close to that corresponding to a thermal equilibrium as the pressure of buffer gases and the temperature of the vapour cell become higher. We have found that the optimal values of the methane pressure, the cell temperature and the cell length can be determined through a kinetic analysis. The conclusions can be valuable for designing configurations of an end-pumped DPAL.

The elemental abundance of deuterium to normal hydrogen in the universe is on the order of 10 −5 . A random distribution would therefore give a ratio of triply deuterated ammonia, ND 3 , to NH 3 of 10 − 15 . Observations indicate an ND 3 to NH 3 ratio of roughly 10 − 3 , implying enrichment of triply deuterated ammonia by about twelve orders of magnitude. A simple model, based on the elemental abundances of N, D and H, is developed and solved analytically. At zero temperature the expressions are particularly simple. Effects of finite temperature are included through the partition functions of the isotopologues. It is found that the effect of finite temperature is modest in the temperature range 10–100 K. The results of the model are in good agreement with the observed abundances so local thermal equilibrium may therefore be a reasonable approximation and thus also be an explanation for the apparent enrichment of deuterated isotopologues.