Population Of Metastable States Research Articles

Effect of matching of a power supply with a laser tube and of pumping conditions on the relaxation of metastable states and the frequency — energy parameters of a copper vapour laser

The relation between the lasing efficiency of a copper vapour laser and relaxation of the metastable states is studied at high average pump powers. The prepulse concentration Nms0 of metastable states in tubes of diameter 2 cm in lasers with a high efficiency (above 1%) is shown to be negligible up to linear output powers of ~50 W m-1 and has no effect on the output power. At a lower lasing efficiency caused by the mismatch between a power supply and the laser tube, the population of metastable states strongly increases during afterglow and can become a main factor restricting the output power in a repetitively pulsed regime. As the neon pressure is increased or hydrogen is added, the matching is facilitated and the effect of Nms0 on the lasing parameters of a high-power copper laser decreases.

Penning collisions of laser-cooled metastable helium atoms

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient β on the excited state ( 23 P 2) and metastable state ( 23 S 1) populations is also investigated. From these results we infer a rather uniform rate constant K sp = (1±0.4)×10-7 cm3/s.

Mössbauer study of the vibrational anisotropy and of the light-induced population of metastable states in single-crystalline guanidinium nitroprusside

Mossbauer studies were performed on single crystals of guanidinium nitroprusside with different orientations of their principal crystallographic axes (a, b, c) with respect to the incident radiation. The markedly anisotropic Lamb-Mossbauer factor f LM , i.e. f LM (a) = 0.118(8), f LM (b) = 0.174(8), f LM (c) = 0.202(8) is in contrast to that of nitroprussides with inorganic anions. The observed anisotropy is ascribed to the anisotropic vibrational mean-square displacement of the nitroprusside anions as a whole which is due to the specific packing of both, anions and cations, as well as the very weak chemical bonding between the ions, typical only for guanidinium nitroprusside. The vibrational anisotropy of iron atoms in barium nitroprusside that has been observed by X-ray structural investigations has a different origin and therefore does not result in an anisotropic Lamb-Mossbauer factor. We have also investigated metastable states in guanidinium nitroprusside that have been populated by means of incoherent irradiation from light-emitting diodes. With a specific orientation of the guanidinium nitroprusside single crystal a population of the metastable states up to 26% could be achieved. Populations of comparable size on lithium, sodium and potassium nitroprussides have only been reached using coherent laser irradiation.

Combined X-ray Diffraction and Density Functional Study of [Ni(NO)(η5-Cp*)] in the Ground and Light-Induced Metastable States

The crystal structure of [Ni(NO)(η5-Cp*)] in the light-induced metastable state was determined by X-ray diffraction at 25 K of a crystal with a 47% metastable-state population. The most significant...

Instrumentation for laser-induced annihilation spectroscopy of metastable antiprotonic helium atoms

We have established a technique for laser resonance spectroscopy of metastable antiprotonic helium atoms (p̄He +) by successfully observing laser-induced annihilation. In this paper, we describe the full instrumentation of the experiment in detail, namely, the particle detectors, the laser system, the cryostat and the helium gas target, the data acquisition and analysis method. For an effective laser triggering selective to 3% metastable antiprotons, a highly efficient detection system for antiproton annihilation was required, with a suppressed inefficiency of less than a percent. Guided by simulations, we designed a system of seven lead-scintillator sandwich counters to detect the charged pions and π 0-decay gamma rays from antiproton annihilation, and achieved 99.7±0.1% efficiency for the detection of annihilation. We employed two identical sets of excimer-pumped dye laser systems with 2–5 mJ output energy per pulse, which were triggered by every metastable antiproton formed in a helium gas target of 0.3–1.0 bar at 4.5–10 k. The resonant deexcitation of the metastable states was detected as a spike-like forced annihilation in the time spectrum, thus revealing the level structure of this exotic atom. This powerful technique enabled us to study also the lifetimes and populations of specific metastable states, by changing the timing and the wavelengths of the laser pulses.

New method to analyze fast metastable atomic beams

By making use of effects of the image charge on projectile trajectories in scattering of a fast beam of metastable He-atoms with keV energies from an Al (111) surface under a glancing angle of incidence, we have developed a new method to analyze fast atomic beams with respect to relative populations of excited metastable states. Based on our experimental studies we propose the construction of a corresponding detector.

Collisional-radiative model for helium and its application to a tokamak plasma

We have reviewed the cross-section data of electron impact excitation for transitions starting from the ground and metastable states, and for those between different − l levels within the same n for neutral helium. We have taken into account the effect of the helium singlet and triplet wave function mixing caused mainly by the spin-orbit interaction. The dependence of the degree of the mixing on the magnetic field strength was also calculated. We have incorporated these data in our collisional-radiative model code and analysed the population of the 3 3 P and 3 3 D levels measured in the WT-3 tokamak plasma. The ground and 2 3 S metastable state populations thus determined are compared with those given by the neutral transport code.

Far-infrared spectroscopy of localized states in indium doped PbTe and Pb 1− xA xTe (A x = Mn 0.017;Sn 0.18) alloys

Far-infrared reflection spectra of indium doped PbTe single crystal as well as of Pb 1− x A x Te alloys (A x = Mn 0.017;Sn 0.18) in the temperature range between 10 and 300 K are presented. Analysis of the spectra was made by a fitting procedure based on the model of coupled oscillators. At temperatures below T = 200 K, two additional modes appear, along with the modes which describe strong plasmon-LO phonon coupling. The first mode, at about 122 cm −1, is a local impurity mode of indium which represents a population of metastable states due to the transfer of electrons from two-electron to one-electron metastable impurity states. The second mode at about 488 cm −1 we believe to appear as a consequence of the electron transfer from a stable impurity two-electron state to the conduction band.

Mechanisms and kinetics of exotic atom formation in hydrogen and helium

The current status of the theory of exotic atom formation in hydrogen and helium is briefly reviewed. The problems of the two-step mechanism of mu-atom formation in molecular hydrogen and of primary populations of hadronic metastable states in helium are discussed.

Raman scattering spectra of indium-doped PbTe

The non-polarized Raman scattering spectra of indium-doped PbTe single crystals were measured in the temperature range between 10 and 300 K. Well resolved peaks at about 68, 126 and 143 cm-1 were observed for all temperatures. An additional mode appears at about 115 cm-1 for temperatures below 100 K. The intensity of this mode increases sharply when the temperature is lowered below 25 K, the temperature where a persistent photoconductivity effect in PbTe(In) appears. This mode is assigned as a local In impurity mode and represents a population of metastable states due to the transfer of electrons from two-electron to one-electron metastable impurity states.

Metastable electronic states induced by nuclear decay and light

Radioactive atoms incorporated in insulating solid-state compounds create various kinds of chemical and physical “after-effects” upon nuclear disintegration. Mossbauer emission spectroscopy of57Co-labelled coordination compounds has undoubtedly become the most informative technique to detect such after-effects like aliovalent charge and spin states of the nucleogenic iron atom resulting from the57Co(EC)57Fe decay, low energy excitations of crystal field and Zeeman states, linkage isomerism, radical formation with subsequent redox reactions, and others. We have extensively studied57Co-labelled complexes with [CoIIN6] cores employing time-integral and time-resolved Mossbauer emission spectroscopy. In complexes of strong ligands fields (where the corresponding synthesized iron(II) complexes show low spin behaviour with1A1 ground slate) and in complexes of intermediate ligand field strength (where the corresponding iron(II) compounds exhibit thermal spin-crossover1A1 ⇌5T2) we have observed the population of metastable high spin states, which is strongly time- and temperature-dependent in the case of the strong-field complexes. Irradiation of iron(II) spin-crossover complexes with light also induces the formation of metastable high spin states, which are the same in nature as those resulting from decaying nuclei as an “intramolecular light source”. The mechanisms for “light-induced excited spin state trapping” (LIESST) and “nuclear decay induced excited spin state trapping” (NIESST) have been elucidated; they are strongly related to each other. In57Co-labelled LiNbO3 and other matrices, we have observed nonthermalized populations of the Zeeman sublevels of the ligand field ground state. These low energy excitations and the metastable ligand field states constitute the last stages of the slowing down process after the nuclear decay.

Time-resolved spectroscopic study of high-pressure self-sustained discharge-pumped atomic xenon lasers

To explore the lasing kinetics of UV-preionized, self-sustained discharge-pumped atomic xenon (5d to 6p) lasers, the time-resolved spectroscopy of the laser output from the multiline laser resonator is reported. The dilutents used were Ar and He. Increasing Xe concentration shortened the 1.73- mu m laser pulse duration and decreased the total (multiline) laser output energy, because increased Xe metastable state population contributes to the increase of the 6p state population (lower laser level) by electron-impact excitation and radiation trapping during discharge pumping. High-excitation-rate pumping resulted in the decrease of the laser output power of 1.73- and 2.63- mu m lines. Increasing the total gas pressure leads to high-efficiency operation due to modest-excitation-rate pumping at high pressures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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PHOTODISSOCIATION OF PbCl2

The population on 6p2 3P2 metastable state and 6p2 3P0 ground state of Pb atoms are de-monstrated, which are originated from dissociating PbCl2 by the fourth harmonic of YAG lasers. The population ratio of 3P2 to 3P0 is measured in terms of laser-induced fluorescence. The results indicate that the dissociation of PbCl2 is a two photon process and the population inversion between 3P2 and 3P0 exists. The stimulated Raman radiation based on the population of 3P2 metastable state is observed. The possible way of dissociation is studied.

Relaxation of metastable copper atoms in a copper bromide vapor laser under regular pulse conditions

An experimental investigation was made of the relaxation of the populations of 2D5/2 and 2D3/2 metastable states of the copper atom in the interpulse period in the active medium of a copper bromide vapor laser under near-optimal lasing conditions. Measurements were resolved over the cross section of the discharge zone. The processes responsible for the observed decay of the metastable state populations were considered. An investigation was made of the influence of hydrogen on the lasing characteristics, the excitation power, and the decay of the metastable-state populations. The reasons for an increase in the output power of a copper bromide vapor laser with added hydrogen are discussed.

Time-Differential Ground-State Hanle Effect in Fast-Beam Laser Spectroscopy

Optical pumping in fast ion-beam collinear laser spectroscopy is used to study the time evolution of oriented metastable state populations in an external magnetic field. A theoretical description of this time-differential ground-state Hanle effect is presented. The possibility to measure ionic ground- and metastable-state $g$ factors is illustrated by a measurement of the $g$-factor ratio of the $5d^{2}D_{\frac{3}{2}}$ and $5d^{2}D_{\frac{5}{2}}$ states in ${\mathrm{Ba}}^{+}$.

Fast-beam laser spectroscopy on metastable atoms applied to neutron-deficient ytternium isotopes

The efficient population of metastable 3P states in charge-transfer neutralization of Yb + beams with Na and Cs has been exploited for studies of isotope shifts in the even neutron-deficient and stable Yb isotopes (156⩽ A⩽176). In addition, measurements have been performed in the intercombination line (5556 Å) from the ground state, primarily to obtain hyperfine structures and isotope shifts for a number of odd isotopes (161⩽ A⩽169). The competitive advantages of different atomic transitions for sensitive high-resolution spectroscopy are discussed.

Efficiency studies of the thallium anti-Stokes Raman laser

Selective photodissociation of TlCl and TlI using 248 nm radiation from a KrF* excimer laser has been used to create a Tl* ( 6p^{2}P\deg_{3/2} ) metastable state population inversion. Stimulated anti-Stokes Raman emission at 376 nm has been observed using a 532 nm pump laser. Output power at the anti-Stokes wavelength and conversion efficiencies are reported.

A model of photostructural changes in chalcogenide vitreous semiconductors: 1. Theoretical considerations

Light-induced processes in chalcogenide vitreous semiconductors are considered in the framework of a configurational model of two stable states (ground and metastable) of atomic units with optical and thermal transitions between these states. Probabilities of these transitions as functions of photon energy and temperature are calculated. an expression for the metastable state population kinetics is given.

On the population of metastable ionic states in electron-capture collisions

The population of metastable states of singly and doubly charged rare-gas ions created by electron capture in keV ion-atom collisions is investigated by means of a subsequent electron stripping or capture collision.