Thermal Equilibrium Of Electrons Research Articles

Resolving transient temperature and density during ultrafast laser ablation of aluminum

To understand the dynamics of ultrashort-pulse laser ablation, the interpretation of ultrafast time-resolved optical experiments is of utmost importance. To this end, spatiotemporally resolved pump-probe ellipsometry may be utilized to examine the transiently changing dielectric function of a material, particularly when compared to two-temperature model simulations. In this work, we introduce a consistent description of electronic transport as well dielectric function for bulk aluminum, which enables unambiguous quantitative predictions of transient temperature and density variations close to the surface after laser excitation. Potential contributions of these temperature and density fluctuations to the proposed optical model are investigated. We infer that after the thermal equilibrium of electrons and lattice within a few picoseconds, the real part of the dielectric function mostly follows a density decrease, accompanied by an early mechanical motion due to stress confinement. In contrast, the imaginary part is susceptible to a complicated interaction between time-varying collision frequency, plasma frequency, and a density dependency of the interband transitions. The models proposed in this study permit an outstanding quantitative prediction of the ultrashort-pulse laser ablation’s final state and transient observables. Consequently, it is anticipated that in the future, these models will provide a quantitative understanding of the dynamics and behavior of laser ablation.Graphical abstract

Preliminary numerical study of three-temperature model investigation of hypersonic oxygen flow under rotational nonequilibrium

The effect of rotational nonequilibrium on the macroscopic parameters of the flow behind a normal shock wave in oxygen gas flow has been examined. The electron thermal equilibrium was taken into account where the electron temperature was equal to the vibrational temperature according to Park’s assumption. Therefore, only the effect of rotational nonequilibrium on the translational and vibrational temperature was analyzed. Rotational and vibrational relaxation time for the O2-O2 and O2-O collisions proposed recently by Andrienko and Boyd are used. Also, the O2 dissociation rates proposed by Kim and Park are used. The results obtained with the three-temperature model well reproduce the data obtained in shock tube for the shock velocity of 4.44 km/s.

Fermi bubbles: high-latitude X-ray supersonic shell

The nature of the bipolar, $\gamma$-ray Fermi bubbles (FB) is still unclear, in part because their faint, high-latitude X-ray counterpart has until now eluded a clear detection. We stack ROSAT data at varying distances from the FB edges, thus boosting the signal and identifying an expanding shell behind the southwest, southeast, and northwest edges, albeit not in the dusty northeast sector near Loop I. A Primakoff-like model for the underlying flow is invoked to show that the signals are consistent with halo gas heated by a strong, forward shock to $\sim$keV temperatures. Assuming ion--electron thermal equilibrium then implies a $\sim10^{56}$ erg event near the Galactic centre $\sim7$ Myr ago. However, the reported high absorption-line velocities suggest a preferential shock-heating of ions, and thus more energetic ($\sim 10^{57}$ erg), younger ($\lesssim 3$ Myr) FBs.

Dielectric response of laser-excited silicon at finite electron temperature

We calculate the dielectric response of excited crystalline silicon in electron thermal equilibrium by adiabatic time-dependent density functional theory (TDDFT) to model the response to irradiation by high-intensity laser pulses. The real part of the dielectric function is characterized by the strong negative behavior at low frequencies due to excited electron-hole pairs. The response agrees rather well with the numerical pump-probe calculations which simulate electronic excitations in nonequilibrium phase immediately after the laser pulse irradiation. The thermal response is also compared with the Drude model which includes electron effective mass and collision time as fitting parameters. We find that the extracted effective masses are in the range of 0.22-0.36 and lifetimes are in the range of 1-14 fs depending on the temperature. The short Drude lifetimes show that strong damping is possible in the adiabatic TDDFT, despite the absence of explicit electron-electron collisions.

English

In the study of thermal equilibrium of the electrons, it is very necessary to use the fluid model method. In this work, effect of the gas density, the electrons initial energy and the electric field on the electron thermal equilibrium is studied. It is found that the steady state can be achieved by increasing the gas density or the inter-electrode distance. If the gas density or the inter-electrode distance are not sufficient, steady state can be achieved by increasing the electric field. The initial energy of the electrons has great effect on the steady state if the electric field is weak and the difference between the initial energy and the electrons mean energy is great, however this problem can be solved by extending the time. It is necessary to make a best combination between the gas density, inter-electrode distance and the electric field to make a modeling by the fluid model method in the best cases of the steady state. A simple formula is given here to find the minimum time required to use the fluid model for E/N ≥ 500 Td.   Key words: Electrons thermal equilibrium, transport properties, fluid model.

Preparation and Visible Emission of Er-Doped 12CaO·7Al2O3 Powder

Er(3+)-doped 12CaO x 7Al2O3 (C12A7:Er3+) powders were prepared using the sol-gel method. X-ray diffraction, micro-Raman spectra and absorption spectra showed that C12A7:Er3+ powder had been obtained. Sharp and intense Er(3+)-related emission from C12A7:Er3+ powder with different Er3+ concentrations in the visible region at room temperature was investigated by analyzing the local structure of Ca atoms in C12A7, and it revealed that cation sites with low symmetry of the host were beneficial to the photoluminescence of Er3+ ions. The emission lines were attributed to two types of Er3+ centers, isolated Er3+ ions and complex centers formed by aggregation of Er3+ ions. The PL intensity might be affected by free oxygen species relative to Er3+ ions formed by charge compensation. The inverse temperature dependent luminescence from the upper level of 2H11/2 state and that from the lower level of 4S3/2 state implied that the thermalization or thermal equilibrium of electrons between the two closely emission states occurred.

Plasma potential in the presence of an external electric field

We studied the mechanism and behavior of a plasma in the presence of an external electric field with a one-dimensional fluid model. We used a two-fluid model, treating both electron and ion motions, rather than a commonly used one-fluid model assuming the electron thermal equilibrium. In particular, we investigated the following issues: (1) the motion of plasma electrons caused by an external static electric field and the formation of a plasma potential; (2) influence of parameters on the plasma potential, which are plasma electron temperature, plasma density, and applied voltage. The plasma potential rises and reaches a value nearly equal to the anode potential in a few nanoseconds. It is higher for a higher anode potential, a higher electron temperature, and a lower plasma density.

Nature of photoluminescence involving transitions from the ground to 4f n−1 5d1 states in rare-earth-doped glasses

Photoluminescence from Er3+ or Pr3+ ion-doped silica or ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass, excited by high-energy photos such as excimer laser photons, was investigated mainly through the temperature dependence. When there are two emission states whose energy difference is small, as in the case of 2H11/2 and 4S3/2 in Er3+ or the 1I6/3P1 mixing state and 3P0 in Pr3+, the luminescence from the upper state and that from the lower state are found to depend inversely on temperature. This indicates that the thermalization or thermal equilibrium of electrons between the two emission states occurs.

Electrical conduction and current noise mechanism in discontinuous metal films. I. Theoretical

A new model of conduction mechanism in discontinuous metal films which gives the temperature dependence of conductivity over a very large temperature interval, from -250 to 450\ifmmode^\circ\else\textdegree\fi{}C, and explains the origin of the conductivity fluctuations responsible for the current noise in these films is presented. It is shown that the conductivity change with temperature is due to a shift of the position of the Fermi level at the surface of the insulator. This changes the height of the potential barrier which must be overcome by tunneling of the conduction electrons. Such a shift, required at each temperature to ensure electron thermal equilibrium, is generated by a partial depletion of surface donor states located on the insulator surface between metal islands. It is further shown that the fluctuation of the surface charge created by the ionization of the surface states modulates the height of the tunneling barrier giving rise to a corresponding modulation of the electrical conductivity originating the current noise typical of discontinuous films. In paper II the results of the theory are compared with experiments.

Spektroskopische Untersuchungen über das thermodynamische Gleichgewicht der Anregung in den Plasmen kurzdauernder Impulsentladungen

The light emission of gases conducting electric discharges is of considerable complexity. The observed phenomenas are controlled to a great part by the electric parameters of the circuit, as well as by the time constants of the specific plasma properties as the relation times for reaching Maxwellian distribution and thermal equilibrium of electrons, ions, and atoms. The influence of the nonequilibrium between the excitation and the electron temperature on the population of states was studied in short time discharges by means of singulet and triplet lines of elements of the second group of the periodic system. In these discharges a nonequilibrium was found between the excitation and the electron temperature. While the time constant measured for the cooling of the electron gas was found to 7·10−7 s in a discharge switched off 9·10−7 s past the ignition the minimal time constant of relaxation of excitation is equal to the life time of the 2p2 state — this value of cadmium being 2.4·10−6 s -.The use of Boltzmann and Saha equation must be considered very carefully in this type of short time discharges.

Thermal Equilibrium of Electrons in Metals: Contact Potentials and Thermoelectric Force.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal Equilibrium of Electrons in Metals: Contact Potentials and Thermoelectric Force.Worth H. RodebushCite this: Chem. Rev. 1927, 4, 3, 255–270Publication Date (Print):October 1, 1927Publication History Published online1 May 2002Published inissue 1 October 1927https://doi.org/10.1021/cr60015a002RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (788 KB) Get e-Alerts Get e-Alerts