Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Linear and circular dichroism in two-step photoionization of barium atoms

Sergei V. Bobashev, N. A. Cherepkov, A. Yu. Elizarov, В. В. Коршунов

Published May 6, 1996• 0 citations

Abstract

The line contour of the autoionizing resonance of 6p7p configuration in barium atoms was experimentally studied in the range of energies 48,000 cm-1 to 54,000 cm-1 with the help of a two-step ionization via intermediate states 6snp(1P1), n equals 6, 7, 8. Using various combinations of polarization of the first- and second-step laser, both linear and circular dichroism were measured in the process of ionization from an excited state.

DOI: 10.1117/12.239765

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Linear and circular dichroism in two-step photoionization of barium atoms

Sergei V. Bobashev, N. A. Cherepkov, A. Yu. Elizarov, В. В. Коршунов

Published May 6, 1996• 0 citations

Publisher

Abstract

DOI: 10.1117/12.239765

Related papers

Linear and circular dichroism in two-step photoionization of barium atoms

Sergei V. Bobashev, N. A. Cherepkov, A. Yu. Elizarov +2 more

The line contour of the autoionizing resonance of 6P7P configuration in barium atoms was experimentally studied in the range of energies. 52,100 cm−1 with the help of a two‐step ionization of via intermediate states 6s6p (1P1), 6s8p (1P1). Using various combinations of polarization of the first‐ and second‐step laser, both linear and circular dichroism were meausred in the process of ionization from an excited state. Theoretical expressions governing linear and circular dichroism are derived. Using these expression, the values of two parameters used in the theory (the ratios of dipole matrix elements from the excited state, squared) were obtained from the experimental data.The line contour of the autoionizing resonance of 6P7P configuration in barium atoms was experimentally studied in the range of energies. 52,100 cm−1 with the help of a two‐step ionization of via intermediate states 6s6p (1P1), 6s8p (1P1). Using various combinations of polarization of the first‐ and second‐step laser, both linear and circular dichroism were meausred in the process of ionization from an excited state. Theoretical expressions governing linear and circular dichroism are derived. Using these expression, the values of two parameters used in the theory (the ratios of dipole matrix elements from the excited state, squared) were obtained from the experimental data.

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Two-step resonant photoionization of free Ni atoms is studied by one-color and two-color processes, using pulsed lasers with photon energies around half the ground-state ionization energy. Two-color two-step resonance ionization from the ground state a ${\mathrm{}}^{3}$ ${\mathit{F}}_{4}$ and the first metastable state a ${\mathrm{}}^{3}$ ${\mathit{D}}_{3}$ via the triplet states z ${\mathrm{}}^{3}$ ${\mathit{G}}_{3,4,5}^{0}$ was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.Two-step resonant photoionization of free Ni atoms is studied by one-color and two-color processes, using pulsed lasers with photon energies around half the ground-state ionization energy. Two-color two-step resonance ionization from the ground state a${\mathrm{}}^{3}$${\mathit{F}}_{4}$ and the first metastable state a${\mathrm{}}^{3}$${\mathit{D}}_{3}$ via the triplet states z${\mathrm{}}^{3}$${\mathit{G}}_{3,4,5}^{0}$ was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.

Physical Review ASep 1, 199626 citations

{)}^{1}

P${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{1}$ and the (5d6p

{)}^{1}

P${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{1}$ states are used as intermediates in the photoexcitation of barium to energies in the range of a series of 5dnd autoionizing states. Dramatic differences in the profiles of autoionizing lines are observed for excitation pathways involving different intermediate states. Angular distributions of photoelectrons collected across the range of autoionizing resonances demonstrate strong variations that follow constraints imposed by the angular momentum of the autoionizing peaks and also suggest significant spin-orbit interactions in the photoionization step.

Stimulated by a recent measurement of coherent control in photoionization of atomic barium, we have calculated one- and two-photon ionization cross sections of the aligned

6s6p\text{ }{^{1}P}_{1}

state of barium in the energy range between the

5{d}_{3/2}

and

5{d}_{5/2}

states of

{\text{Ba}}^{+}

. We have also measured these photoionization spectra in the same energy region, driving the one- or two-photon processes with the second or first harmonic of a tunable dye laser, respectively. Our calculations employ the eigenchannel

R

-matrix method and multichannel quantum defect theory to calculate the rich array of autoionizing resonances in this energy range. The nonresonant two-photon process is described using lowest-order perturbation theory for the photon-atom interactions, with a discretized intermediate-state one-electron continuum. The calculations provide an absolute normalization for the experiment, and they accurately reproduce the rich resonance structures in both the one- and two-photon cross sections, and confirm other aspects of the experimental observations. These results demonstrate the ability of these computationally inexpensive methods to reproduce experimental observables in one- and two-photon ionization of heavy alkaline earths, and they lay the groundwork for future studies of the phase-controlled interference between one- and two-photon ionization processes.

{\mathrm{}}^{3}

{\mathit{F}}_{4}

and the first metastable state a

{\mathrm{}}^{3}

{\mathit{D}}_{3}

via the triplet states z

{\mathrm{}}^{3}

{\mathit{G}}_{3,4,5}^{0}

was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states. Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states. \textcopyright{} 1996 The American Physical Society.