Atomic Thallium Research Articles

Measurement of the Stark-induced amplitudes of the 6P1/2-->7P1/2 transition in atomic thallium.

Measurement of the Stark-induced amplitudes of the 6P1/2-->7P1/2 transition in atomic thallium.

Analysis of atomic electric dipole moment in thallium by all-order calculations in many-body perturbation theory.

A procedure is presented for calculations of double-perturbation problems in the coupled-cluster formalism. With use of this method to include to all orders the correlation effects of single and pair excitations, the enhancement factor R=-585 is obtained for the electric dipole moment (EDM) in atomic thallium. Equations for EDM perturbed single-excitation amplitudes are solved by diagonalization to take into account mixing between excited core states, and perturbed pair functions are introduced to incorporate correlation effects. Considering contributions from higher-order perturbation terms, we estimate the accuracy of the obtained enhancement factor is approximately at the 5--10 % level.

Infrared (0.9–1.65 μm) emission from thallium iodide photoexcited with ultraviolet excimer laser radiation

The infrared emission spectra from 0.9 to 1.65 μm produced when thallium iodide vapor is photodissociated by excimer laser wavelengths of 193, 248, 308, and 351 nm are reported. In this spectral region, only atomic thallium transitions were observed. No emission from metastable atomic iodine at 1.315 μm (5 2P1/2→5 2P3/2) or thallium at 1.283 μm (6 2P3/2→6 2P1/2) was ever detected in contrast to strong 1.315 μm signals obtained by ultraviolet (UV) excimer laser dissociation of C3F7I. The failure to detect metastable atomic emission from TlI photodissociation is explained by the fast quenching of the metastable states during superelastic collision with electrons produced by photoionization of the TlI. Consequently, a pulsed iodine 1.315 μm laser based on photodissociation of thallium iodide does not seem practical.

Relaxation of 6 2P3/2 metastable and 6 2P1/2 ground state atomic thallium produced in the photodissociation of thallium halide vapors at high densities

Decay rates of the 6 2P3/2 metastable and 6 2P1/2 ground state atomic thallium densities produced in UV photodissociation (at λ193, 222, 249, 308, and 353 nm) of TlI, TlBr, and TlCl molecular vapors have been measured for vapor densities from 1013 to 1017 cm−3. Dominant relaxation processes have been identified as (i) for the metastable state, collisional deexcitation by thallium halide molecules at high halide densities (≥1015 cm−3) and by free halogens and trace impurities at lower halide densities and (ii) for the ground state, diffusion in the ambient (argon/thallium halide) gas at high halide densities and volume reassociation under certain conditions at low halide densities. Cross sections and diffusion coefficients are evaluated.

Hg2TI is an Intermetallic Compound

Abstract By means of a toroidal oscillating viscometer, the shear viscosity of some mercury thallium alloys has been measured in the composition range 33–33.5 atomic percent thallium and over the temperature range from 13.5–16.5°C. Some discussion of the experimental results is given in terms of liquid coordination number.

Stimulated emission in thallium iodide vapour pumped with an ArF flashlamp

Thallium iodide has been photodissociated with the radiation of an ArF flashlamp excited by a longitudinal discharge. Stimulated emission from atomic thallium on the transition at 535 nm is demonstrated. The pulse-form has been analysed and the dependence of the emission on the pump power has been measured. Parameters of the flashlamp and the laser output are compared with a computer stimulation of the laser process.

Cross sections for production of atomic thallium states in photodissociation of thallium halides

The cross sections for production of 62P1/2 and 62P3/2 ground and metastable atomic thallium states via UV dissociation of the thallium halides TlCl, TlBr, and TlI have been measured at wavelengths 193, 222, 249, 308, and 353 nm using time-resolved atomic resonance absorption spectroscopy. The measured cross sections, which were independent of halide densities up to densities ∼1017 cm−3, were found to represent only 10% to 36% of the total UV absorption cross section at the appropriate wavelength.

Relative yields of metastable and ground-state thallium atoms following photodissociation of thallium halides

The relative yields of metastable (6 2P 3 2 ) and ground- (6 2P 1 2 ) state atomic thallium produced after the photodissociation of TlCl, TlBr and TlI by the output of a rare-gas halide laser operating at 193, 222, 249, 308 and 353 nm have been measured. Resonance-line and broadband absorption spectroscopy have been used to determine the temporal evolution of the metastable and ground-state densities, allowing the measurement of the relative yields to halide densities in excess of 10 16 cm −3.

Viscosity of Hg5Tl2at 14.5°C

Abstract By means of a toroidal oscillating viscometer, the shear viscosity of some mercury-thallium alloys has been measured in the composition range 28.5–29.5 atomic percent thallium and over the temperature range from 12.5–15.5°C. Some discussion of the experimental results is given in terms of liquid coordination number.

Resonances in the low-energy scattering of electrons by atomic thallium

Results for the low-energy (0-5 eV) scattering of electrons by atomic Tl are presented. The resonance structure is analysed and a comparison is made between a non-relativistic and a relativistic R-matrix calculation which takes into account parts of the Breit-Pauli Hamiltonian. Total cross sections for the transitions (6p)2P1/2 to (6p)2P1/2,3/2, (7s)2S1/2, (7p)2P1/2,3/2 and (6d)2D3/2,5/2 are given.

Parity Nonconservation in Atomic Thallium

We present new measurements of parity conservation in the 293-nm transition in atomic $_{81}^{205}\mathrm{Tl}$. Linearly polarized 293-nm photons, polarization $\stackrel{^}{\ensuremath{\epsilon}}$, are absorbed by $6^{2}P_{\frac{1}{2}}$ atoms in crossed electric and magnetic fields. The transition probability for each Zeeman component contains a term proportional to $\stackrel{^}{\ensuremath{\epsilon}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}\stackrel{^}{\ensuremath{\epsilon}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{E}}\ifmmode\times\else\texttimes\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ arising from interference between the Stark $E1$ amplitude $\ensuremath{\beta}E$ and the parity-nonconserving $E1$ amplitude ${\mathcal{E}}_{p}$. Our result, ${[\mathrm{Im}\frac{{\mathcal{E}}_{p}}{\ensuremath{\beta}}]}_{\mathrm{expt}}=\ensuremath{-}1.73\ifmmode\pm\else\textpm\fi{}0.33$ mV/cm, is compared with estimates based on the standard electroweak model.

Switching of photon-echo polarization and direction by coherent optical fields

We report a novel method for the observation of photon echoes and other coherent transient effects. In this method, the polarization, direction, and frequency of the polarized coherent radiation emitted by a system are switched by optical pulses. We apply this method to detect photon echoes generated on the $6{P}_{\frac{1}{2}}\ensuremath{-}7{S}_{\frac{1}{2}}$ transition in atomic thallium by two collinear and vertically polarized excitation pulses which are separated by 20 nsec. At the time of the echo, two orthogonally polarized probe pulses resonant with the $6{P}_{\frac{3}{2}}\ensuremath{-}7{S}_{\frac{1}{2}}$ transition of atomic thallium are applied to the sample to switch the photon echo from its original polarization and direction. A horizontally polarized photon echo with its propagation vector turned by about 10 mrad and its axis of polarization rotated by 90\ifmmode^\circ\else\textdegree\fi{} is detected. No electro-optical shutter is used in the experiment. The echo signal disappears either when one of the probe pulses is blocked or when both probe pulses are horizontally or vertically polarized. Echo polarization switching is also demonstrated using an unpolarized probe pulse applied prior to the echo formation time.

Magneto-optical studies of atomic thallium centers in KCl: Magnetic circular dichroism tagged by spin resonance

We report measurement of the magnetic circular dichroism (MCD) of radiation-damaged crystals of KCl doped with Tl. By using microwaves resonant with ground-state magnetic splittings, we have been able to tag such MCD spectra to specific species. In particular, we have shown that bands peaking at 1040, 725, 550, 405, 340, and 254 nm all belong to the ${\mathrm{Tl}}^{0}$(1) center, where that center, as determined by earlier spin-resonance studies, consists of a neutral Tl atom perturbed by the field of an adjacent anion vacancy. Our experiment constitutes the first direct evidence that a recently discovered, thallium-associated, laser-active center whose pump band peaks at 1040 nm is indeed the ${\mathrm{Tl}}^{0}$(1) center; furthermore, the MCD of the two lowest energy bands are in rough quantitative agreement with predictions of a simple electronic model of that center. Finally, our technique has allowed the discovery of two other centers having distinctly different spin resonances, yet whose optical spectra bear some striking similarities to that of the ${\mathrm{Tl}}^{0}$(1) center. Because their fundamental bands overlap those of the ${\mathrm{Tl}}^{0}$(1) center, the new centers may affect the operation of ${\mathrm{Tl}}^{0}$(1)-center lasers.

Observation and density dependence of the Raman echo in atomic thallium vapor

Working on the 6P12−6P32 transition of atomic thallium vapor, we have observed Raman echoes generated by excitation and probe fields detuned from the 7S12 intermediate state by up to 50 cm-1. This constitutes the first time that echoes, generated by pure two-photon excitation, have been observed in an atomic system. The Raman echo intensity is found to increase roughly as the square of the thallium density at low densities, but at higher densities it peaks and subsequently declines. We suggest that two-photon absorption and loss of phase-matching resulting from excitation-pulse-induced population transfer are important in the high density degradation of the Raman echo signal.

First-Principle Analysis of Strength of Parity Nonconservation in Atomic Thallium by Relativistic Many-Body Theory

With use of relativistic many-body perturbation theory, ${E}_{1}=(1.51\ifmmode\pm\else\textpm\fi{}0.07)(i{\ensuremath{\mu}}_{\mathrm{B}}{Q}_{W})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ has been obtained for the $6{P}_{\frac{1}{2}}\ensuremath{\rightarrow}7{P}_{\frac{1}{2}}$ dipole transition matrix element in the presence of parity-nonconserving weak electron-nucleon interaction effects explicitly, which on combination with the available experimental ${M}_{1}$ leads, for ${{sin}^{2}\ensuremath{\theta}}_{\mathrm{W}}=0.23$, to $\ensuremath{\delta}=(1.65\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3} \mathrm{and} (1.68\ifmmode\pm\else\textpm\fi{}0.25)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ respectively, for $^{203}\mathrm{Tl}$ and $^{205}\mathrm{Tl}$ in good agreement with the most recent experimental result for $\ensuremath{\delta}$.

Atomic thallium laser and Tl-Hg excimer formation by two photon dissociation of TlI and Hg mixtures

TlI vapor is photodissociated in a two photon process using 249 nm and 351 nm excimer laser radiation. In the presence of Hg buffer gas, stimulated emission of atomic Tl at 535 nm and broadband Tl-Hg excimer emission are observed. Dynamics of this process with possible implications for an optically pumped Tl-Hg excimer laser are discussed.

Efficient operation of an atomic thallium photodissociation laser at 535.0 nm

Results of experiments investigating the influence of resonance radiation trapping on the power and efficiency of the atomic thallium photodissociation laser are reported. Transverse pumping of a thallium iodide cell with added free metallic thallium has enabled conversion efficiencies from the ArF laser pump beam of greater than 7% to be achieved on a single Tl laser transition at λ 535.0 nm. Collisional deexcitation of the 72S1/2 upper laser level imposes a limit on the TlI densities which can be employed.

New Observation of Parity Nonconservation in Atomic Thallium

Refined observations of parity nonconservation in the $6^{2}P_{\frac{1}{2}}\ensuremath{-}7^{2}P_{\frac{1}{2}}$ transition in $_{81}^{203,\phantom{\rule{0ex}{0ex}}205}\mathrm{Tl}$ are reported. Absorption of circularly polarized 293-nm photons by $6^{2}P_{\frac{1}{2}}$ atoms in an $E$ field results in polarization of the $7^{2}P_{\frac{1}{2}}$ state, through interference of the Stark $E1$ amplitude with $M1$ and parity-nonconserving $E1$ amplitudes. Detection of this polarization yields the circular dichroism $\ensuremath{\delta}=+(2.8\ifmmode\pm\else\textpm\fi{}{1.0}{0.9})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which agrees with theoretical estimates based on the Weinberg-Salam model, for ${{sin}^{2}\ensuremath{\theta}}_{W}=0.23$.

Gain in a thallium iodide laser with external resonator

An atomic thallium laser at 535 and 377.6 nm with an external resonator, excited by photodissociating thallium iodide with the emission of an ArF excimer laser, has been built. Gain and stimulated emission cross section are determined.

Electronic structure for the ground state of TlH from relativistic multiconfiguration SCF calculations

The dissociation curve for the ground state of TlH was computed using a relativistic ω–ω coupling formalism. The relativistic effects represented by the Dirac equation were introduced using effective potentials generated from atomic Dirac–Fock wave functions using a generalization of the improved effective potential formulation of Christiansen, Lee, and Pitzer. The multiconfiguration SCF treatment used is a generalization of the two-component molecular spinor formalism of Lee, Ermler, and Pitzer. Using a five configuration wave function we were able to obtain approximately 85% of the experimental dissociation energy. Our computations indicate that the bond is principally sigma in form, despite the large spin–orbit splitting in atomic thallium. Furthermore the bond appears to be slightly ionic (Tl+H−) with about 0.3 extra electron charge on the hydrogen.