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Journal of Physics B Atomic Molecular and Optical Physics

Energy transfer in mercury vapour following laser excitation of the 71S0state by two-photon absorption

N. Bras, J. C. Jeannet, D. Perrin

Published Aug 14, 1993• 6 citations
Publisher

Abstract

After excitation of the 7 1 S 0 mercury state by two photon absorption of a laser radiation at 313 nm the time integrated intensities of the 407.8 (I 0 ) and 404.7 nm (I 1 ) lines emitted from the 7 1 S 0 and 7 3 S 1 states were determined as functions of the pump laser intensity, I, and mercury pressure. At high pump laser intensities I 0 and I 1 do not follow anymore a quadratic law in I, I 0 weakens to I n<2 while, in contrast, I 1 increases to I n>2 . The time evolutions of the populations of these 7 1 S 0 , 7 3 S 1 states and of the 6 1 P 1 , 6 3 P 0,1,2 states were determined. The set of experimental results is well reproduced by introducing collisions of two Hg(6P) atoms as well as two Hg(7 1 S 0 ) collisions. Effects of these collisions are discussed.

DOI
10.1088/0953-4075/26/15/015

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The transfer of excitation from excited mercury atoms to ground-state thallium atoms was investigated using techniques of sensitized fluorescence. A Hg–Tl vapor mixture contained in a quartz cell was irradiated with Hg 2537 Å resonance radiation which caused the mercury atoms to become excited to the 63P1, state. Subsequent collisions between the Hg(63P1) and Tl(62P1/2) atoms resulted in the population of the 82S1/2, 62D, and 72S1/2 thallium states, whose decay gave rise to sensitized fluorescence of wavelengths 3231, 3520, 3776, and 5352 Å. Intensity measurements on the sensitized fluorescence and on the Hg 2537 Å resonance fluorescence, observed at right angles to the direction of excitation, yielded cross sections of 3.0, 0.3, and 0.05 Å2 for collisional excitation transfer from Hg(63P1) to the 82S1/2, 62D, and 72S1/2 states in thallium, respectively. The results are fully consistent with previously determined cross sections for excitation transfer in other binary metallic vapor systems.

Canadian Journal of Physics•Jul 1, 1978•10 citations
After excitation of the 7 1 S 0 mercury state by two photon absorption of a laser radiation at 313 nm the time integrated intensities of the 407.8 (I 0 ) and 404.7 nm (I 1 ) lines emitted from the 7 1 S 0 and 7 3 S 1 states were determined as functions of the pump laser intensity, I, and mercury pressure. At high pump laser intensities I 0 and I 1 do not follow anymore a quadratic law in I, I 0 weakens to I n<2 while, in contrast, I 1 increases to I n>2 . The time evolutions of the populations of these 7 1 S 0 , 7 3 S 1 states and of the 6 1 P 1 , 6 3 P 0,1,2 states were determined. The set of experimental results is well reproduced by introducing collisions of two Hg(6P) atoms as well as two Hg(7 1 S 0 ) collisions. Effects of these collisions are discussed.
Cross sections for 6^D, 7^D and 8^0 fine-structure mixing in Rb, induced in collisions with various ground-state atoms and N2 molecules, have been determined using methods of atomic fluorescence.Rb vapour, pure or mixed with a buffer gas, was irradiated in a glass fluorescence cell with pulses of radiation from a N2 laser-pumped dye laser, populating a fine-structure state by two-photon absorption.The resulting fluorescence included a direct component emitted in the decay of .the optically excited state and a sensitized component due to the col1isional1y populated fine-structure state.Measure ments of relative intensities of the two components in relation to buffer gas (or Rb vapour) pressure yielded the following cross sections.-14 2 Inelastic Cross sections (10 cm ) process Rb He Ne Ar Kr Xe I would like to express sincere thanks to Professor L.
Excitation transfer between 6s6d Hg fine-structure states, induced by collisions with Hg, Ar and N 2 , was studied using methods of fluorescence spectroscopy in a vapour cell. Hg vapour, pure or mixed with Ar or N 2 , was excited to the 6 1 D 2 or 6 3 D 2 state by two-photon absorption and the relative intensities of the fluorescence components emitted from the radiatively and collisionally populated states were determined using a monochromator and a photomultiplier. Measurements of the fluorescent intensity ratios in relation to the density of the collision partner yielded the total thermally averaged cross sections for the transfers 1 D 2 to 3 D 2 , 1 D 2 to 3 D 3 3 D 2 to 3 D 3 , and 3 D 2 to 1 D 2 , with Hg, Ar and N 2 as collision partners.
A new type of electron/photon coincidence experiment is presented which utilises a laser -electron stepwise excitation technique to prepare atoms in an excited state. An electron collision initially excites an atom from the ground state to an intermediate state. Following this electron excitation process, coherent single mode laser radiation further excites the atom to an upper state, from which the fluorescence is observed. The nature of the laser excitation transfers both amplitude and phase information about the electron excited state to the upper excited state in a coherent way. This information is extracted from the upper state fluorescence by analysis of the fluorescence polarization in coincidence with the electron scattered from the atom for particular polarizations of the laser radiation. The coincidence technique allows an identically prepared sub -ensemble of excited atoms to be selected for measurement. The electron excited state studied was the 61131 state of mercury, excited by a beam of unpolarized electrons at an impact energy of 16 eV. The mercury atomic beam was isotopically selected following electron excitation using the narrow bandwidth of the laser radiation. Excitation from the electron excited 61P1 state was via 579 nm laser radiation to the 61D2 state and fluorescence was monitored from this state to the 63P1 state via a 313 nm transition. Stokes parameters were measured for two different laser polarization angles, since this allowed a complete set of collision parameters to be deduced for a single experimental geometry. Results for three different scattering angles at this energy are presented. The laser excitation process was modelled in both the weak and the strong laser excitation regimes. A perturbation approach developed to model single photon laser excitation allowed the collision parameters to be extracted from the measured coincidence Stokes parameters analytically, whereas a Quantum Electrodynamic model allowed high laser intensity effects on the coincidence signal to be explored theoretically. The Quantum Electrodynamic model indicated that the weak excitation model could be used to extract the collision parameters from the Stokes parameters at the laser intensities used in the experiment. Effects due to variation of the laser intensity were predicted from the Quantum Electrodynamic model and experiments conducted to test these predictions are presented. Collision parameters deduced from the measured stepwise coincidence Stokes parameters following optimization of the experimental conditions are presented. These parameters are compared qualitatively with existing data from heavy atomic systems and with a theoretical model based upon the Distorted Wave Born Approximation. Similarities between the experimental data are found, however significant discrepancies are noted between the parameters obtained here and with the predictions of the theoretical model.
Inclusion of collisional destruction mechanisms as sink terms in the theory of imprisonment of resonance radiation appears to have been neglected in the case of the 2537-Å mercury line. In this paper, the Holstein photon transport equation is employed to determine the effect of destructive or self-quenching collisions between resonance state and ground state atoms, processes in which the resonance state is converted to another excited state with the release of kinetic energy. These mechanisms seem to explain experimental work in which the decay constant of the 2537-Å mercury line reaches a minimum and then increases with density. Comparison of theory with experimental data yields a cross section between 3.0 and 10.0 × 10−18 for the conversion of Hg(3P1) to metastable Hg(3P0) by two-body collisions with Hg(1S0). The sharp increase at high density of the decay constant of the 2537-Å mercury line has not been predicted by previous theories but is a general consequence of the inclusion of collisional destruction mechanisms.
Collisional transfer of excitation from mercury to sodium was investigated using methods of sensitized fluorescence. A mixture of mercury and sodium vapors at low pressure was irradiated with Hg 2537 Å resonance radiation, producing a population of Hg(63P1) atoms whose inelastic collisions with ground-state sodium atoms resulted in a transfer of excitation energy to close-lying S, P, and D states in sodium. The subsequent decay of these states manifested itself in the emission of a sensitized fluorescent spectrum. Absolute intensity measurements on the components of the spectrum yielded 21 cross sections whose magnitudes range from 0.02 to 38.5 Å2 and which exhibit a pronounced resonance with ΔE, the energy defect between Hg (63P1) and the appropriate level in sodium.
The transfer of excitation from excited mercury atoms to ground-state thallium atoms was investigated using techniques of sensitized fluorescence. A Hg–Tl vapor mixture contained in a quartz cell was irradiated with Hg 2537 Å resonance radiation which caused the mercury atoms to become excited to the 63P1, state. Subsequent collisions between the Hg(63P1) and Tl(62P1/2) atoms resulted in the population of the 82S1/2, 62D, and 72S1/2 thallium states, whose decay gave rise to sensitized fluorescence of wavelengths 3231, 3520, 3776, and 5352 Å. Intensity measurements on the sensitized fluorescence and on the Hg 2537 Å resonance fluorescence, observed at right angles to the direction of excitation, yielded cross sections of 3.0, 0.3, and 0.05 Å2 for collisional excitation transfer from Hg(63P1) to the 82S1/2, 62D, and 72S1/2 states in thallium, respectively. The results are fully consistent with previously determined cross sections for excitation transfer in other binary metallic vapor systems.