Journal of Physics Conference Series

Electron Spectroscopy of strontium in the vicinity of four-photon excitation of the 5p2 1S0state

Anastasios Dimitriou, S. Cohen

Published Sep 7, 2015• 0 citations

Abstract

We present experimental photoelectron energy spectra and angular distributions from multiphoton ionization of Sr by dye laser pulses of ∼ns duration in the wavelength range of 715-737 nm and relatively low intensity (≈4 × 10 11 W·cm -2 ). The selected wavelength range comprises the highly correlated 5p 2 1 S 0 autoionizing state, excited by four photons. Our results reveal the dominant (single and double) ionization pathways that were obscured in earlier experiments, based solely on the recording of ion and ionic-fluorescence yields.

DOI: 10.1088/1742-6596/635/9/092049

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Single and double ionization of strontium in the vicinity of four-photon excitation of the 5p2 1S0doubly excited state

Ioannis Liontos, S. Cohen, Agisilaos Bolovinos

Journal of Physics B Atomic Molecular and Optical PhysicsFeb 11, 200813 citations

Fluorescence studies of multiphoton ionization of Sr: Production of excited ionic states

Harold K. Haugen, Andreas Othonos

Physical Review ADec 1, 19885 citations

Multiphoton single and double ionisation of strontium in the range 532-541 nm

Pierre Camus, Μιχάλης Κομπίτσας, S. Cohen +4 more

Journal of Physics B Atomic Molecular and Optical PhysicsFeb 14, 198926 citations

Fluorescence studies of multiphoton ionization of Ca and Sr: Emission from highly excited ionic states

Harold K. Haugen, Henrik Stapelfeldt

Physical Review AFeb 1, 199212 citations

Fluorescence studies of multiple-photon ionization processes: Four- and five-photon ionization of Sr at wavelengths of 558–590 nm

Harold K. Haugen, Andreas Othonos

Physical Review AApr 1, 198911 citations

Path dependence in resonant multiphoton excitation to autoionizing states of barium

James S. Keller, John E. Hunter, R. Stephen Berry

Physical Review AMar 1, 199119 citations

Journal of Physics Conference Series

Electron Spectroscopy of strontium in the vicinity of four-photon excitation of the 5p2 1S0state

Anastasios Dimitriou, S. Cohen

Published Sep 7, 2015• 0 citations

Publisher

Abstract

DOI: 10.1088/1742-6596/635/9/092049

Related papers

Single and double ionization of strontium in the vicinity of four-photon excitation of the 5p2 1S0doubly excited state

Ioannis Liontos, S. Cohen, Agisilaos Bolovinos

We report on the single and double multiphoton ionization of ground state Sr atoms observed in an atomic beam experiment with laser pulses of ∼5 ns duration, maximum intensity ∼4 × 10 11 W cm −2 and within the 710–740 nm wavelength range. The Sr + spectrum consists of two strong lines originating from three-photon resonant four-photon ionization of bound states, a number of weak autoionizing resonances and a broad line due to four-photon excitation of the doubly excited 5p 2 1 S 0 state. The latter, along with a strong, broad and structured spectral feature, is also evident in the wavelength dependence of the doubly charged Sr 2+ ion. A weakly evident but reproducible inflection point ('knee' structure) appears in the intensity dependence of the Sr 2+ yield at the location of the 5p 2 1 S 0 resonance. A complementary fluorescence experiment revealed the accumulation of population in the 5p 1/2 , 3/2 , 6s 1/2 and 5d 3/2 , 5/2 excited Sr + states during the laser pulse. All fluorescence signals depend on laser wavelength in a manner similar to the recorded Sr + spectrum. The population accumulation in the 5p 1/2 , 3/2 ionic states unambiguously proves the absorption of two photons above the first 5s 1/2 atomic threshold while that of the 5d 3/2 , 5/2 and 6s 1/2 ones suggest the absorption of at least two more. Since under our laser pulse duration and intensity the absorption of such a number of photons in an unstructured continuum is highly improbable, it may be concluded that the process is mediated by dense manifolds of near- resonant doubly excited states, their role in the dynamics of laser–atom interaction under our conditions being far more crucial than in studies conducted using intense ultrashort pulses.We report on the single and double multiphoton ionization of ground state Sr atoms observed in an atomic beam experiment with laser pulses of ∼5 ns duration, maximum intensity ∼4 × 10 11 W cm −2 and within the 710–740 nm wavelength range. The Sr + spectrum consists of two strong lines originating from three-photon resonant four-photon ionization of bound states, a number of weak autoionizing resonances and a broad line due to four-photon excitation of the doubly excited 5p 2 1 S 0 state. The latter, along with a strong, broad and structured spectral feature, is also evident in the wavelength dependence of the doubly charged Sr 2+ ion. A weakly evident but reproducible inflection point ('knee' structure) appears in the intensity dependence of the Sr 2+ yield at the location of the 5p 2 1 S 0 resonance. A complementary fluorescence experiment revealed the accumulation of population in the 5p 1/2 , 3/2 , 6s 1/2 and 5d 3/2 , 5/2 excited Sr + states during the laser pulse. All fluorescence signals depend on laser wavelength in a manner similar to the recorded Sr + spectrum. The population accumulation in the 5p 1/2 , 3/2 ionic states unambiguously proves the absorption of two photons above the first 5s 1/2 atomic threshold while that of the 5d 3/2 , 5/2 and 6s 1/2 ones suggest the absorption of at least two more. Since under our laser pulse duration and intensity the absorption of such a number of photons in an unstructured continuum is highly improbable, it may be concluded that the process is mediated by dense manifolds of near- resonant doubly excited states, their role in the dynamics of laser–atom interaction under our conditions being far more crucial than in studies conducted using intense ultrashort pulses.

Journal of Physics B Atomic Molecular and Optical PhysicsFeb 11, 200813 citations

Fluorescence studies of multiphoton ionization of Sr: Production of excited ionic states

Harold K. Haugen, Andreas Othonos

Multiphoton ionization of strontium in the wavelength range of \AA{}558-590 nm is studied via the fluorescence from excited ${\mathrm{Sr}}^{+}(5p^{2}P_{\frac{3}{2},\frac{1}{2}})$ ions. The fine-structure sublevels in the singly charged ion are fully resolved and are found to be nonstatistically populated. Four- and five- (or more) photon processes are observed to populate ${\mathrm{Sr}}^{+}(5p^{2}P)$ in the intensity regime of $I\ensuremath{\sim}1\ensuremath{-}50$ GW/ ${\mathrm{cm}}^{2}$ , but no emission is detected from higher-lying states of ${\mathrm{Sr}}^{+}$ .Multiphoton ionization of strontium in the wavelength range of \AA{}558-590 nm is studied via the fluorescence from excited ${\mathrm{Sr}}^{+}(5p^{2}P_{\frac{3}{2},\frac{1}{2}})$ ions. The fine-structure sublevels in the singly charged ion are fully resolved and are found to be nonstatistically populated. Four- and five- (or more) photon processes are observed to populate ${\mathrm{Sr}}^{+}(5p^{2}P)$ in the intensity regime of $I\ensuremath{\sim}1\ensuremath{-}50$ GW/${\mathrm{cm}}^{2}$, but no emission is detected from higher-lying states of ${\mathrm{Sr}}^{+}$.

Physical Review ADec 1, 19885 citations

Multiphoton single and double ionisation of strontium in the range 532-541 nm

Pierre Camus, Μιχάλης Κομπίτσας, S. Cohen +4 more

By focusing an excimer pumped dye laser on an atomic beam, the authors have observed multiphoton multiple ionisation of the neutral strontium atom in the tuned wavelength range 532-41 nm. Sr + and Sr ++ yields were measured with a time of flight spectrometer. At least three photons are required to produce Sr + and eight photons to produce Sr ++ . As a function of the wavelength, the Sr + yield exhibits resonances which correspond to two-photon excitation of bound states (5s 2 -5p 2 1 D 2 and 5s 2 -5p 2 1 S 0 ) and three-photon excitation of autoionising states 4d5f J=1 and J=3 of the neutral atom. The Sr ++ yield exhibits four broad smooth resonances that they interpret, from known spectroscopic data, as two-photon (5p 1/2 -4f), three-photon (5s-6p 1/2, 3/2 ) and four-photon (5s-7d) resonances in the singly charged ion. The latter transitions start from a singly charged ion in the 5s or 5p 1/2 state reached after three- or four-photon ionisation of the neutral ground state. The variation of the Sr ++ pattern as a function of the dye laser beam intensity shows that resonances are shifted and broadened when the intensity is increased. These features have been interpreted by a perturbative treatment of Sr + ionisation based on the use of an effective Hamiltonian which takes into account higher-order terms involved in the calculation of resonance effects. Calculated multiphoton ionisation probabilities are in good agreement with experimental data.By focusing an excimer pumped dye laser on an atomic beam, the authors have observed multiphoton multiple ionisation of the neutral strontium atom in the tuned wavelength range 532-41 nm. Sr + and Sr ++ yields were measured with a time of flight spectrometer. At least three photons are required to produce Sr + and eight photons to produce Sr ++ . As a function of the wavelength, the Sr + yield exhibits resonances which correspond to two-photon excitation of bound states (5s 2 -5p 2 1 D 2 and 5s 2 -5p 2 1 S 0 ) and three-photon excitation of autoionising states 4d5f J=1 and J=3 of the neutral atom. The Sr ++ yield exhibits four broad smooth resonances that they interpret, from known spectroscopic data, as two-photon (5p 1/2 -4f), three-photon (5s-6p 1/2, 3/2 ) and four-photon (5s-7d) resonances in the singly charged ion. The latter transitions start from a singly charged ion in the 5s or 5p 1/2 state reached after three- or four-photon ionisation of the neutral ground state. The variation of the Sr ++ pattern as a function of the dye laser beam intensity shows that resonances are shifted and broadened when the intensity is increased. These features have been interpreted by a perturbative treatment of Sr + ionisation based on the use of an effective Hamiltonian which takes into account higher-order terms involved in the calculation of resonance effects. Calculated multiphoton ionisation probabilities are in good agreement with experimental data.

Journal of Physics B Atomic Molecular and Optical PhysicsFeb 14, 198926 citations

Fluorescence studies of multiphoton ionization of Ca and Sr: Emission from highly excited ionic states

Harold K. Haugen, Henrik Stapelfeldt

Multiphoton ionization of Ca and Sr was studied at a wavelength of 532 nm with optical pulses of 12-ns and 35-ps duration. Excess photon absorption followed by autoionizing decay leads to populations of excited states of singly charged ions that can be observed via their spontaneous emission. Relative measurements were performed on fluorescence from ${\mathrm{Ca}}^{+}$ (4p), ${\mathrm{Ca}}^{+}$ (5s), and ${\mathrm{Ca}}^{+}$ (4d), and from ${\mathrm{Sr}}^{+}$ (5p) and ${\mathrm{Sr}}^{+}$ (6s). The contribution of the highly excited states was found to be favored under short-pulse (35-ps) irradiation.Multiphoton ionization of Ca and Sr was studied at a wavelength of 532 nm with optical pulses of 12-ns and 35-ps duration. Excess photon absorption followed by autoionizing decay leads to populations of excited states of singly charged ions that can be observed via their spontaneous emission. Relative measurements were performed on fluorescence from ${\mathrm{Ca}}^{+}$(4p), ${\mathrm{Ca}}^{+}$(5s), and ${\mathrm{Ca}}^{+}$(4d), and from ${\mathrm{Sr}}^{+}$(5p) and ${\mathrm{Sr}}^{+}$(6s). The contribution of the highly excited states was found to be favored under short-pulse (35-ps) irradiation.

Physical Review AFeb 1, 199212 citations

Fluorescence studies of multiple-photon ionization processes: Four- and five-photon ionization of Sr at wavelengths of 558–590 nm

Harold K. Haugen, Andreas Othonos

An ``all-optical'' technique is presented for the study of multiphoton-ionization processes, based on fluorescence detection of the ions which are produced. A vapor is utilized in a moderate-density regime (\ensuremath{\sim} ${10}^{11}$ -- ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) such that collisional effects are negligible. The technique is applied to multiple-photon ionization of Sr in the wavelength range of 558--590 nm at laser intensities \ensuremath{\sim}1--50 GW/ ${\mathrm{cm}}^{2}$ . Fine-structure-resolved emission of the ${\mathrm{Sr}}^{+}$ (5 ${p}^{2}$ ${P}_{3/2/,1/d}^{0}$ ) ions which are formed is observed at \ensuremath{\lambda}=407.8 and 421.5 nm, following either four- or five-photon absorption. No emission is observed from higher ionic states, with a detection sensitivity \ensuremath{\sim} ${1:10}^{3}$ with respect to the ionic-resonance emission.An ``all-optical'' technique is presented for the study of multiphoton-ionization processes, based on fluorescence detection of the ions which are produced. A vapor is utilized in a moderate-density regime (\ensuremath{\sim}${10}^{11}$--${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) such that collisional effects are negligible. The technique is applied to multiple-photon ionization of Sr in the wavelength range of 558--590 nm at laser intensities \ensuremath{\sim}1--50 GW/${\mathrm{cm}}^{2}$. Fine-structure-resolved emission of the ${\mathrm{Sr}}^{+}$ (5${p}^{2}$${P}_{3/2/,1/d}^{0}$) ions which are formed is observed at \ensuremath{\lambda}=407.8 and 421.5 nm, following either four- or five-photon absorption. No emission is observed from higher ionic states, with a detection sensitivity \ensuremath{\sim}${1:10}^{3}$ with respect to the ionic-resonance emission.

Physical Review AApr 1, 198911 citations

Path dependence in resonant multiphoton excitation to autoionizing states of barium

James S. Keller, John E. Hunter, R. Stephen Berry

We measure photoion spectra and angular distributions of photoelectrons from the two-color, two-photon resonant ionization of barium atoms in order to probe the effect of the photoionization pathway on autoionization processes. The (6s6p ${)}^{1}$ 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.We measure photoion spectra and angular distributions of photoelectrons from the two-color, two-photon resonant ionization of barium atoms in order to probe the effect of the photoionization pathway on autoionization processes. The (6s6p${)}^{1}$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.

Physical Review AMar 1, 199119 citations

Multiphoton ionization of strontium in the wavelength range of \AA{}558-590 nm is studied via the fluorescence from excited

{\mathrm{Sr}}^{+}(5p^{2}P_{\frac{3}{2},\frac{1}{2}})

ions. The fine-structure sublevels in the singly charged ion are fully resolved and are found to be nonstatistically populated. Four- and five- (or more) photon processes are observed to populate

{\mathrm{Sr}}^{+}(5p^{2}P)

in the intensity regime of $I\ensuremath{\sim}1\ensuremath{-}50$ GW/

{\mathrm{cm}}^{2}

, but no emission is detected from higher-lying states of

{\mathrm{Sr}}^{+}

{\mathrm{Ca}}^{+}

(4p),

{\mathrm{Ca}}^{+}

(5s), and

{\mathrm{Ca}}^{+}

(4d), and from

{\mathrm{Sr}}^{+}

(5p) and

{\mathrm{Sr}}^{+}

(6s). The contribution of the highly excited states was found to be favored under short-pulse (35-ps) irradiation.

{10}^{11}

{10}^{15}

${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) such that collisional effects are negligible. The technique is applied to multiple-photon ionization of Sr in the wavelength range of 558--590 nm at laser intensities \ensuremath{\sim}1--50 GW/

{\mathrm{cm}}^{2}

. Fine-structure-resolved emission of the

{\mathrm{Sr}}^{+}

{p}^{2}

{P}_{3/2/,1/d}^{0}

) ions which are formed is observed at \ensuremath{\lambda}=407.8 and 421.5 nm, following either four- or five-photon absorption. No emission is observed from higher ionic states, with a detection sensitivity \ensuremath{\sim}

{1:10}^{3}

with respect to the ionic-resonance emission.

{)}^{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.