Population Of Metastable Levels Research Articles

Type-I intermittency route to chaos in passively Q-switched Tm:YLF laser emitting at 2.3 μm

We report on an original chaotic dynamic behaviour of a passively Q-switched 2.3-μm Thulium laser operating on the 3H4 → 3H5 transition. The experiment employs a Tm:LiYF4 laser crystal within various laser cavity configurations, involving optional additional cascade laser operation on the 3F4 → 3H6 transition at 1.9 μm. The saturable absorber employed is Cr2+:ZnSe, which is exclusively saturated by the 2.3 μm laser emission. A precise analysis of the Q-switching dynamics shows a pronounced inclination of the cascade laser scheme towards chaotic operation. To investigate the origins of chaos, we originally monitor the metastable 3F4 level population using cascade laser operation at 1.9 μm, which proves to be a crucial underlying parameter for explaining the observed instabilities. This analysis allows for explaining the specific dynamics of the Q-switched 2.3 μm Tm-laser intrinsically linked to Tm3+-doped materials. A very atypical route to chaos for a Q-switched laser is demonstrated involving type I intermittencies. The obtained results are of great interest for studying the premises of chaos in pulsed solid-state lasers.

Insights into Density and Location Diagnostics of Photoionized Outflows in X-Ray Binaries

The population of metastable levels is key to high-precision density diagnostics of astrophysical plasmas. In photoionized plasmas, density is used to infer the distance from the ionizing source, which is otherwise difficult to obtain. Perfecting models that compute these populations is thus crucial. The present paper presents a semianalytic hydrogenic approximation for assessing the relative importance of different processes in populating atomic levels. This approximation shows that in the presence of a radiation source, photoexcitations and collisional excitations are both important over a wide range of plasma temperatures and ionizing spectra, while radiative recombination is orders of magnitude weaker. The interesting case of Fe+21 with a collisional radiative model with photoexcitation demonstrates this effect. The population of the first excited metastable level in Fe+21 is sensitive to the electron number density in the critical range of n e = 1012–1015 cm−3; it was observed to be significantly populated in the X-ray spectrum of the 2005 outburst of the X-ray binary GRO J1655-40. The present model shows that photoexcitation is the predominant process indirectly populating the metastable level. For the photoionized plasma in the GRO J1655-40 outflow, the model indicates a measured value of n e = (2.6 ± 0.5) × 1013 cm−3, implying a distance from the source of r = (4.4 ± 0.4) × 1010 cm. Finally, we show how the computed critical density and distance of Fe+21 yield the correct ionization parameter of the ion, independent of ionization balance calculations.

Diagnostic study of capacitively coupled neon rf plasma with traces of O2/H2 at intermediate pressure

In this work, we have performed the non-invasive diagnostic study of capacitively coupled Ne–O2/H2 mixture plasma through the optical emission spectroscopy (OES) coupled with a suitable collisional radiative (CR) model. Capacitively coupled neon radio-frequency (rf) discharge (flowing downstream) with small admixture of O2/H2 have been generated in a vacuum chamber using 13.56 MHz rf signal and 120 W power supply. Keeping O2 and H2 flow rates fixed at 0.01 and 0.015 LPM respectively, the neon flow rate has been varied as 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 LPM to obtain different mixture concentration of Ne–O2 and Ne–H2 discharge. The pressure in the chamber has been observed in intermediate range (∼500–25 000 Pa) for different mixture concentrations. OES measurements are recorded at various operating conditions in the wavelength range from 200 to 1200 nm. To extract the information of plasma parameters from the OES measurements, a comprehensive fine-structure resolved CR model has been developed. In the diagnostic process, five intense Ne–I emission lines at 594.48, 607.43, 633.44, 638.30, 703.24 nm are used. The CR model considers all the important processes i.e. electron impact excitation, electron impact de-excitation, radiative decay, ionization, two–three body recombination, and diffusion. The quenching process of 1s (1s5,1s4,1s3) levels of neon by the O2/H2 molecule has been included in the model. The radiative transitions from the upper levels to the ground state (1S0) as well as to the 1s levels of neon are corrected for self-absorption. The electron temperature (T e) and electron density (n e) of the plasma have been extracted for all the mixture concentrations of Ne–O2 and Ne–H2. Also, with the different mixture concentrations of O2/H2 in neon discharge, the variation of population of metastable levels (1s5, 1s3) of neon as well as intensities of 656.28 nm of hydrogen and 777.4 nm of oxygen lines have been reported and discussed.

Large-Volume CuBr-Laser with the Possibility of Continuous Control for Generation of Energy

Results of designing and studying a prototype of an active element on copper bromide vapors with continuous control of the energy of each radiation pulse are presented. It is distinct feature in featuring implementation of the above mode for a gas-discharge tube with a large volume (above 1.5 L) and formation of the radiation by an unstable cavity. In doing this, a hydrogen-containing addition was used to modify the plasma kinetics with the aim to increase the radiation power. The control was implemented due to the use of an additional preionization pulse. The dependence of the generation powerat each wavelength on the energy of the preionization pulse and time delay between this pulse and excitation pulses is obtained. It is shown that population of metastable levels of copper atoms is the main factor in the control for generation in the designed prototype.

Double Electric Layer of a Helium Discharge in Modulation Mode

The positive column of a helium gas discharge in modulation mode has been investigated. It has been revealed that the contribution of the stepwise ionization to population of the 31D2 level is low due to small population of metastable levels at weak discharge currents (20–100 mA). With increasing discharge current, the metastable atom population increases and hence, the modulation depth of spectral line intensities of metastable levels also increases. At high currents (>100 mA), the modulation depth of spectral line intensities decreases because of saturation of metastable level population.

CuBr-лазер большого объема c возможностью непрерывного управления энергией генерации

The paper presents the results of research and development of the copper bromide active element with continuous control of the each pulse energy. Distinctive features are the implementation of the continious control mode for a large-volume gas discharge tube (more than 1.5 L) and the radiation formation by an unstable resonator. In this case, a hydrogen-containing additive was used to modify the plasma kinetics in order to increase the radiation power. The control was carried out through the use of an additional preionization pulse. The dependences of the generation power on each line on the preionization pulse energy and the time delay between this pulse and the excitation pulse are obtained. It is shown that in the developed layout, the determining factor in pulse energy controlling is the population of metastable levels of copper atoms.

Advances in neutral tungsten ultraviolet spectroscopy for the potential benefit to gross erosion diagnosis

A spectral survey of tungsten emission in the ultraviolet region has been completed in the DIII-D tokamak and the CTH torsatron to assess the potential benefit of UV emission for the diagnosis of gross W erosion. A total of 29 W I spectral lines are observed from the two experiments using survey spectrometers between 200 and 400 nm with level identifications provided based on a structure calculation for many of the excited states that produce strong emission lines. Of the 29 observed lines, 20 have not previously been reported in fusion relevant plasmas, including an intense line at 265.65 nm which could be important for benchmarking the frequently exploited line at 400.88 nm. Nearly all of the observed spectral lines decay down to one of the six lowest energy levels for neutral W, which are likely to be long-lived metastable states. The impact of metastable level populations on the W I emission spectrum and any erosion measurement utilizing a spectroscopic technique is potentially significant. Nevertheless, the high density of W I emission in the UV region allows for the possibly of determining the relative metastable fractions and plasma parameters local to the erosion region. Additionally, the lines observed in this work could be used to perform multiple independent gross erosion measurements, leading to more accurate diagnosis of gross tungsten erosion.

Reflectivity of Superimposed Bragg Gratings Induced by Longitudinal Mode Instabilities in Fiber Lasers

We report on reflectivity of transient Bragg gratings created in the active medium of a fiber laser with longitudinal mode instability. Despite the long history of laser physics, reflectivities of such gratings were theoretically studied and experimentally measured only recently. Based on the coupled-mode theory, we derived a theoretical model of superimposed Bragg gratings for a special case of mode instability known as spontaneous laser line sweeping (SLLS). SLLS fiber lasers exhibit a periodic wavelength drift over an interval of several nanometers, followed by a quick bounce backward, narrowband, and mostly single-frequency operation as well as pulsed output with pulse lengths on the order of microseconds. The refractive index modulation inside the active fiber is given by the Kramers–Kronig relations. For ytterbium, the refractive index change in the 1060-nm band is directly proportional to the metastable level population with a factor of ${\text{2.1}}\times {\text{10}}^{- 31}\,{\text{m}}^{3}$ . Taking into account realistic values of temporal damping of the gratings, significant reflectivity on the order of units to tens of percent is estimated. The reflectivity can be controlled by setting the SLLS laser parameters. Effect of the resonator length is shown as an example.

Formation of metastable molecular states at the resonance scattering of two atoms in a laser radiation field

Using the Dirac’s method, the formation of metastable molecular states at the resonance scattering of two atoms in the laser radiation field is considered. Expressions for the metastable level populations and the resonance scattering cross sections are obtained. In the case of an exact resonance with the laser radiation, the graphs for populations and resonance scattering cross sections, which have two peaks due to the Autler–Townes effect, are obtained. These results play an important role in the study of the controlled chemical reaction and for the understanding of the processes in the quantum systems of the Bose–Einstein condensate at low temperatures, as well as in the various optical processes in atomic gases.

Particle detection through the quantum counter concept in YAG:Er3+

We report on a scheme for particle detection based on the infrared quantum counter concept. Its operation consists of a two-step excitation process of a four level system, which can be realized in rare earth-doped crystals when a cw pump laser is tuned to the transition from the second to the fourth level. The incident particle raises the atoms of the active material into a low lying, metastable energy state, triggering the absorption of the pump laser to a higher level. Following a rapid non-radiative decay to a fluorescent level, an optical signal is observed with a conventional detector. In order to demonstrate the feasibility of such a scheme, we have investigated the emission from the fluorescent level 4S3∕2 (540 nm band) in an Er3+-doped YAG crystal pumped by a tunable titanium sapphire laser when it is irradiated with 60 keV electrons delivered by an electron gun. We have obtained a clear signature that this excitation increases the 4I13∕2 metastable level population that can efficiently be exploited to generate a detectable optical signal.

Measurements of the populations of metastable and resonance levels in the plasma of an RF capacitive discharge in argon

The behavior of the populations of two metastable and two lower resonance levels of argon atoms in the plasma of an RF capacitive discharge was studied. The populations were measured by two methods: the method of emission self-absorption and the method based on measurements of the intensity ratios of spectral lines. It is shown that the populations of resonance levels increase with increasing power deposited in the discharge, whereas the populations of metastable levels is independent of the RF power. The distribution of the populations over energy levels is not equilibrium under these conditions. The population kinetics of argon atomic levels in the discharge plasma is simulated numerically. The distribution function of plasma electrons recovered from the measured populations of atomic levels and numerical simulations is found to be non-Maxwellian.

X-RAY AND EUV SPECTROSCOPY OF VARIOUS ASTROPHYSICAL AND LABORATORY PLASMAS: COLLISIONAL, PHOTOIONIZATION AND CHARGE-EXCHANGE PLASMAS

Several laboratory facilities were used to benchmark theoretical spectral models those extensively used by astronomical communities. However there are still many differences between astrophysical environments and laboratory miniatures that can be archived. Here we setup a spectral analysis system for astrophysical and laboratory (SASAL) plasmas to make a bridge between them, and investigate the effects from non-thermal electrons, contribution from metastable level-population on level populations and charge stage distribution for coronal-like, photoionized, and geocoronal plasmas. Test applications to laboratory measurement (i.e. EBIT plasma) and astrophysical observation (i.e. Comet, Cygnus X-3) are presented. Time evolution of charge stage and level population are also explored for collisional and photoionized plasmas.

The host-galaxy response to the afterglow of GRB 100901A

For Gamma-Ray Burst 100901A, we have obtained Gemini-North and Very Large Telescope optical afterglow spectra at four epochs: one hour, one day, three days and one week after the burst, thanks to the afterglow remaining unusually bright at late times. Apart from a wealth of metal resonance lines, we also detect lines arising from fine-structure levels of the ground state of Fe II, and from metastable levels of Fe II and Ni II at the host redshift (z = 1.4084). These lines are found to vary significantly in time. The combination of the data and modelling results shows that we detect the fall of the Ni II 4 F9/2 metastable level population, which to date has not been observed. Assuming that the population of the excited states is due to the UV-radiation of the afterglow, we estimate an absorber distance of a few hundred pc. This appears to be a typical value when compared to similar studies. We detect two intervening absorbers (z = 1.3147, 1.3179). Despite the wide temporal range of the data, we do not see significant variation in the absorption lines of these two intervening systems.

Measurement of Relative Metastable Level Population of Gd Atoms in Hollow Cathode Lamp with LIF Method

Relative metastable level population of metal plasma having low-lying metastable states departs from equi-librium value. It needs to be experimentally investigated. This paper reports the use of hollow cathode lamp based Laser Induced Fluorescence (LIF) spectroscopy technique to measure Relative metastable level popu-lation of metal in a plasma produced by a hollow cathode lamp. The relative population of ground state and 533 cm-1 levels of Gd atoms in hollow cathode lamp is measured with LIF method.

Ozone-stimulated emission due to atomic oxygen population inversions in an argon microwave plasma torch

It is shown that, in a microwave torch discharge in an argon jet injected into an oxygen atmosphere at normal pressure, quasi-resonant energy transfer from metastable argon atoms to molecules of oxygen and ozone generated in the torch shell and, then, to oxygen atoms produced via the dissociation of molecular oxygen and ozone leads to the inverse population of metastable levels of atomic oxygen. As a result, the excited atomic oxygen with population inversions becomes a gain medium for lasing at wavelengths of 844.6 and 777.3 nm (the 33P–33S and 35P–35S transitions). It is shown that an increase in the ozone density is accompanied by an increase in both the lasing efficiency at these wavelength and the emission intensity of the plasma-forming argon at a wavelength of 811.15 nm (the 2P04s–2P04p transition). When the torch operates unstably, the production of singlet oxygen suppresses ozone generation; as a result, the lasing effect at these wavelengths disappears.

Correlation of prepulse plasma parameters with metastable level population and their effect on lasing characteristics of the pulsed copper vapor laser

The effect of the prepulse electron density and population of the lower laser (metastable) level on lasing characteristics of the pulsed copper vapor laser is considered. In the analysis of their effect, attention is paid to the need to consider the correlation of these parameters. It is emphasized that the effect of the prepulse electron density depends on the electron heating rate at the beginning of the excitation pulse. The conditions controlling the electron heating rate and methods for reducing the effect of this parameter are considered.

The Ionized Gas and Nuclear Environment in NGC 3783. V. Variability and Modeling of the Intrinsic Ultraviolet Absorption

We present results on the location, physical conditions, and geometry of the outflow in the Seyfert 1 galaxy NGC 3783 from a study of the variable intrinsic UV absorption. Based on analysis of 18 observations with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and 6 observations with the Far Ultraviolet Spectroscopic Explorer obtained between 2000 February and 2002 January, we obtain the following results: 1) The lowest-ionization species detected in each of the three strong kinematic components (components 1 – 3 at radial velocities −1350, −550, and −725 km s −1 , respectively) varied, with equivalent widths inversely correlated with the continuum flux. This indicates the ionization structure in the absorbers responded to changes in the photoionizing flux, with variations occurring over the weekly timescales sampled by our observations. 2) A multi-component model of the line-of-sight absorption covering factors, which includes an unocculted narrow emission-line region (NLR) and separate covering factors derived for the broad line region and continuum emission sources, predicts saturation in several lines, consistent with the lack of observed variability in these lines. Differences in covering factors and kinematic structure imply component 1 is comprised of two physically distinct regions (1a and 1b). 3) We obtain column densities for the individual metastable levels from the resolved C III* λ1175 absorption complex in component 1a. Based on our computed metastable level populations, the electron density of this absorber is ∼ 3×10 4 cm −3 . Combined with photoionization modeling results, this places component 1a at ∼ 25 pc from the central source. 5) Using time-dependent calculations, we are able to reproduce the detailed variability observed in component 1 and derive upper limits on the distances for components 2 and 3 of ≤ 25 and ≤ 50 pc, respectively. 6) The ionization parameters derived for the higher ionization UV absorbers (components 1b, 2, and 3 with log(U)≈ −0.5) are consistent with the modeling results for the lowest-ionization X-ray component, but with smaller total column density. The high-ionization UV components are found to have similar pressures as the three X-ray ionization components. These results are consistent with an inhomogeneous wind model for the outflow in NGC 3783, with denser, colder, lower-ionization regions embedded in more highly-ionized gas. 7) Based on the predicted emission-line luminosities, global covering factor constraints, and distances derived for the UV absorbers, they may be identified with emission-line gas observed in the inner NLR of AGNs. We explore constraints for dynamical models of AGN outflows implied by these results. Subject headings: galaxies: individual (NGC 3783) — galaxies: active — galaxies: Seyfert — ultraviolet: galaxies

Evidence for explosive event activity originating in the chromosphere

We report on a joint SUMER, CDS, TRACE study, concentrating on a region which shows prolonged EUV explosive event (EE) activity in the transition region line N v 1238 Å, yet little evidence of such activity in another transition region line O v 629 Å (formed at a similar temperature) which was observed simultaneously. A possible explanation for the lack of major activity in the O v line in several explosive events could be that they originate in the lower chromosphere. This is consistent with the enhancements in the C i 1249 Å line and with the findings of another study which reported time delays between the chromospheric and transition region lines in some EE's using high cadence observations (10 s exposure time) obtained with the SUMER spectrometer in H i Ly 6 (20 000 K) and S vi (200 000 K). Using the generalized collisional-radiative picture, including the population of metastable levels, we derive the density dependent contribution function for both N v 1238 and O v 629 for four values of the electron density; 106 cm-3 representing the low density limit, 109 cm-3 for a typical quiet Sun electron density plus 1011 cm-3 and 1012 cm-3 for an active region. These calculations show that with increasing electron density, both lines shift to slightly lower temperatures. However, the major difference is in the relative increase in the line flux with increasing density. For N v, increasing the density to 1011 cm-3 results in a 60% increase in the line flux, while O v shows a 30% decrease. Increasing the electron density to 1012 cm-3 results in a factor of two decrease in the O v flux, thus making it difficult to detect explosive event activity in this line if the event is formed in the chromosphere. Other explosive events which show simultaneous activity in both lines are probably formed in the transition region. In one such event, activity is observed in both N v and O v, yet nothing in C i. In this event we also observe an increase in the TRACE 173 emission, delayed by ≈40 s compared to the transition region lines.

Measurement of the populations of metastable levels in gadolinium vapor by diode laser-based UV and near-IR absorption spectroscopy

The metastable populations of gadolinium atoms, which were generated by an electron beam gun, were measured by diode laser-based absorption spectroscopy. Transitions originating out of the ground and low-lying metastable levels were investigated in the spectral range of 390–394 nm. A tapered semiconductor power-amplifier which was seeded by a single-mode external-cavity diode laser was used as a fundamental light source for the second-harmonic generation in the ultraviolet wavelength range. The population appears to be frozen at an atomic excitation temperature of ∼600 K, which is about 1/4 of the heated surface temperature. The results obtained from the ultraviolet absorption spectra are compared to those obtained from the near-IR absorption spectra with wavelength ranges of 673–692 and 773–775 nm.

Dissociative excitation of odd sextet levels of the manganese atom in the e-MnCl2 collisions

The dissociative excitation of odd sextet levels of the manganese atom in collisions between slow electrons and manganese dichloride molecules was studied experimentally. The cross sections for the population of the metastable a6D levels (the lower levels of the laser transitions) by cascade transitions have been determined. It is established that for the z6F° and z6D° levels, the cross sections for both the dissociative and direct excitation, Qm and Qa, respectively, differ only slightly in absolute value. For the x6P° levels, the ratio Qa/Qm amounts to 9–11, but for the upper laser levels it is much larger: 33 for the z6P° level and 240 for the y6P° level.