Population Densities Of Excited Levels Research Articles

On the population density of the argon excited levels in a high power impulse magnetron sputtering discharge

Population densities of excited states of argon atoms in a high power impulse magnetron sputtering (HiPIMS) discharge are examined using a global discharge model and a collisional-radiative model. Here, the ionization region model (IRM) and the Orsay Boltzmann equation for electrons coupled with ionization and excited states kinetics (OBELIX) model are combined to obtain the population densities of the excited levels of the argon atom in a HiPIMS discharge. The IRM is a global plasma chemistry model based on particle and energy conservation of HiPIMS discharges. OBELIX is a collisional-radiative model where the electron energy distribution is calculated self-consistently from an isotropic Boltzmann equation. The collisional model constitutes 65 individual and effective excited levels of the argon atom. We demonstrate that the reduced population density of high-lying excited argon states scales with (p*)−6, where p* is the effective quantum number, indicating the presence of a multistep ladder-like excitation scheme, also called an excitation saturation. The reason for this is the dominance of electron impact processes in the population and de-population of high-lying argon states in combination with a negligible electron–ion recombination.

Spectroscopic properties and dynamic analysis of three-photon quantum-cutting luminescence in Er doped NaYF4 nanoparticles

Spectroscopic properties and dynamic analysis play a significant role during the design and development of novel luminescent materials. In this work, Er3+ doped NaYF4 nanoparticles were successfully synthesized by coprecipitation method. The absorption spectrum, fluorescence spectra, and decay curves were measured at room temperature. The spectroscopic properties, including the radiative and nonradiative transition probability, fluorescent branch ratio, cross-relaxation rate and the fluorescence lifetime, were calculated based on the Judd-Ofelt theory. Furthermore, the rate equation models were established to analyze the dynamic processes of three-photon near-infrared quantum cutting luminescence. The time-dependent population densities of excited levels of Er3+ ions were simulated and the theoretical quantum efficiency was calculated to be 252.40%, which is consistent with our experimental results.

The influence of excitation inhomogeneities on energy transfer upconversion measurements

The authors investigate the effect of excitation inhomogeneities on the temporal behavior of the population density of excited levels when energy transfer upconversion (ETU) processes are present. The results show that the spatial shape of the excitation energy may affect the decays when the nonlinear processes are important. A procedure to deal with this problem as well as to obtain a better fit of the experimental upconversion parameters is presented.

Studies of a Magnetic Neutral Loop Discharge Based on Laser Diagnostics of Electron Behavior and Atomic Processes

In order to understand plasma formation processes in a neutral loop discharge, measurements of population densities of excited levels of helium atoms were performed using laser induced fluorescence (LIF) spectroscopy. At the same time, profiles of electron density n e and electron temperature T e were measured using Thomson scattering. The results of these measurements were analyzed using a collisional-radiative model of helium atoms in the plasma. It was found that population densities of excited levels of the helium atoms were consistent with the values of n e and T e. This indicates that it is not necessary to consider an existence of a high energy electron component which may be supposed to theoretically exist in addition to the Maxwellian energy distribution function for the bulk of electrons at the measured temperature T e. Also, it was shown that the energy deposition to electrons in the vicinity of the neutral loop plays a essential role in the formation of the neutral loop discharge plasma.

Determination of the electron temperature from partial LTE populations in a mercury plasma flow

Population densities of excited levels of mercury atoms were measured in a supersonic plasma flow. Existence of partial LTE permitted determination of the electron temperature from the slope of the Boltzmann plot.

A collisional-radiative model for helium and its application to a discharge plasma

For the collisional-radiative model applied to helium, two alternative formulations are presented in which non-linear process such as ionization due to metastable-metastable collisions may be included. The atomic data, including dielectronic,recombination, employed in the calculations are summarized. The collisional-radiative calculation is applied to a positive-column plasma for which both the nonlinear processes and radiation trapping are taken into account. The calculated population densities of excited levels for a low-pressure and low-current discharge plasma show good agreement with a measurement made using the hook method. The population density distribution among excited levels is interpreted in terms of excitation-ionization mechanisms in the plasma. This leads to a grouping of the excited levels into two phases for the discharge plasma considered: the corona phase applies to the lower-lying levels and the quasi-saturation phase to the higher-lying levels. The importance of the ladder-like excitation-ionization mechanism is noted for this class of plasmas.

Collisional-Radiative Calculation of the Population Inversion in the Argon Ion Laser

The collisional-radiative and population coefficients are calculated on singly ionized argon to estimate the population densities of excited levels and the population inversion in a typical argon laser plasma. The output power calculated from the population inversion is in good agreement with the experimental data so far reported. The saturation and quenching of the inversion at high-level excitation is interpreted in terms of the processes which contribute to the pumping and depletion of laser upper level. It is suggested that radiation trapping for the transition from 3d to the ground level increases the population inversion in large bore tubes.

Experimenteller Nachweis stationärer Inversionen atomarer Niveaus in einem expandierenden Wasserstoff-Plasma / Eperimental Evidence for Stationary Population Inversions of Atomic Levels in an Expanding Hydrogen Plasma

Abstract Detailed calculations of population densities of excited levels in a decaying hydrogen plasma flow predict population inversions within a definite range of plasma parameters. This has been verified experimentally in a rapid expanding plasma where the characteristic time of decay was much shorter than the relaxation time of the ground state. Population inversions have been found for the first transitions of the Paschen and Brackett series

Über das nichtthermische Gleichgewicht in einer Helium-Hohlikathodenentladung

The non-thermal plasma in a helium hollow cathode discharge is analysed by means of experiments and theory. The population densities of excited levels are calculated by a system of equations, including the different processes which occur in the plasma. A detailed examination of the mechanism of exitation and deexcitation follows. From this, a refined method is developed for the determination of the electron temperature by the intensity of a helium line.