Physical Review A

Direct observation of two-photon optical ionizing collisions in crossed lithium atomic beams

Penelope Polak-Dingels, Regina E. Bonanno, John Keller, J. Weiner, J. C. Gauthier

Published May 1, 1982• 6 citations

Abstract

We report here the direct observation of a two-step, ionizing "optical collision" between crossed lithium beams in which very-long-range coupling, due to van der Waals' resonance force between identical particles, is followed by photoionization: ${\mathrm{Li}}^{*}(2p)+\mathrm{Li}(2s)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{*}(3d)+\mathrm{Li}(2s),$ ${\mathrm{Li}}^{*}(3d)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{+}+e.$ Cross-section magnitude and form of the intensity profile are described by a simple three-level model. These results suggest that polarization of the laser field together with collisional two-photon ionization may be used to delineate the shape of individual molecular-state potential curves at long range.

DOI: 10.1103/physreva.25.2539

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Production of Ba+ in a two-photon radiative collision in crossed Na-Ba beams

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Direct observation of a two-photon radiative ionisation collision in crossed Na-Ba atomic beams

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Physical Review A

Direct observation of two-photon optical ionizing collisions in crossed lithium atomic beams

Penelope Polak-Dingels, Regina E. Bonanno, John Keller, J. Weiner, J. C. Gauthier

Published May 1, 1982• 6 citations

Publisher

Abstract

{\mathrm{Li}}^{*}(2p)+\mathrm{Li}(2s)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{*}(3d)+\mathrm{Li}(2s),

{\mathrm{Li}}^{*}(3d)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{+}+e.

Cross-section magnitude and form of the intensity profile are described by a simple three-level model. These results suggest that polarization of the laser field together with collisional two-photon ionization may be used to delineate the shape of individual molecular-state potential curves at long range.

DOI: 10.1103/physreva.25.2539

Related papers

Production of Ba+ in a two-photon radiative collision in crossed Na-Ba beams

John Keller, J. Weiner

We report the observation of a two-step radiative collisional ionization between ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})$ and $\mathrm{Ba}({6s}^{2} ^{1}S_{0})$ in which an optical photon is absorbed simultaneously with the collision, ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})+\mathrm{Ba}({6s}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\mathrm{Na}(3s ^{2}S_{\frac{1}{2}})$ and with subsequent photoionization of the excited barium, ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+}+e$. We observe peak ion intensity close to the difference frequency between ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})$ and ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})$ as well as a quadratic increase of ion intensity with laser power. These results confirm, complement, and extend the interpretation of an earlier observation.We report the observation of a two-step radiative collisional ionization between ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})$ and $\mathrm{Ba}({6s}^{2} ^{1}S_{0})$ in which an optical photon is absorbed simultaneously with the collision, ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})+\mathrm{Ba}({6s}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\mathrm{Na}(3s ^{2}S_{\frac{1}{2}})$ and with subsequent photoionization of the excited barium, ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+}+e$. We observe peak ion intensity close to the difference frequency between ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})$ and ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})$ as well as a quadratic increase of ion intensity with laser power. These results confirm, complement, and extend the interpretation of an earlier observation.

Physical Review AApr 1, 19845 citations

Direct observation of a two-photon radiative ionisation collision in crossed Na-Ba atomic beams

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The authors report the observation of a two-step process in which Na*(4d) is first populated by a radiative collision between Na(3s) and Ba*(6p) in the presence of an intense optical field i.e. Na(3s)+Ba*(6s6p 1 P)+h(cross) omega to Na*(4d)+Ba(6s 2 1 S) followed by photoionisation of the excited sodium Na*(4d)+h(cross) omega to Na + +e. The peak ion intensity is observed at a laser frequency close to the energy difference between Na*(4d) and Ba*(6s6p 1 P), and the magnitude of the cross section for the first step agrees well with theory.The authors report the observation of a two-step process in which Na*(4d) is first populated by a radiative collision between Na(3s) and Ba*(6p) in the presence of an intense optical field i.e. Na(3s)+Ba*(6s6p 1 P)+h(cross) omega to Na*(4d)+Ba(6s 2 1 S) followed by photoionisation of the excited sodium Na*(4d)+h(cross) omega to Na + +e. The peak ion intensity is observed at a laser frequency close to the energy difference between Na*(4d) and Ba*(6s6p 1 P), and the magnitude of the cross section for the first step agrees well with theory.

Journal of Physics B Atomic and Molecular PhysicsJan 28, 19827 citations

Observation of Structure in Laser-Induced Penning and Associative Ionization in Crossed-Beam Na + Na Collisions

Penelope Polak-Dingels, J. F. Delpech, J. Weiner

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Physical Review LettersJun 23, 198064 citations

Penning and associative ionization in crossed-beam Na/Na collisions assisted by strong resonant laser fields

J. Weiner, Penelope Polak-Dingels

We observe the production of Na2+ and Na+ arising from single collisions between crossed beams of sodium atoms when a laser field is tuned near the Na(3p 2P3/2) and Na(3p 2P1/2) transitions. Measurements of ion intensity vs laser intensity show that at moderately high power true laser-induced processes dominate over purely collisional effects. Relative intensity of mass-selected ions produced at either member of the Na resonance doublet shows conclusively that Na+ does not arise simply from photodissociation of Na2+ but must result from a direct, laser-induced collisional ionization.We observe the production of Na2+ and Na+ arising from single collisions between crossed beams of sodium atoms when a laser field is tuned near the Na(3p 2P3/2) and Na(3p 2P1/2) transitions. Measurements of ion intensity vs laser intensity show that at moderately high power true laser-induced processes dominate over purely collisional effects. Relative intensity of mass-selected ions produced at either member of the Na resonance doublet shows conclusively that Na+ does not arise simply from photodissociation of Na2+ but must result from a direct, laser-induced collisional ionization.

The Journal of Chemical PhysicsJan 1, 198140 citations

Relevance of dissociative molecular states for resonant two-center photoionization of heteroatomic dimers

F. Grüll, Alexander B Voitkiv, Carsten Müller

Abstract Photoionization of a weakly bound van-der-Waals dimer, composed of two atomic speciesAandB, is studied theoretically. AtomAcan be ionized either directly or via an indirect two-center channel, where atomBis first resonantly photoexcited and, afterwards, transfers the excitation energy via long-range electron–electron correlations radiationlessly to atomA, causing its ionization. By taking the vibrational nuclear motion of the dimer during the process into account, we analyze the contributions to the photoionization cross section from bound and dissociative molecular states in the final A+ –Bsystem. For the specific example of a LiHe dimer we show (a) that substantial contributions to both ionization mechanisms result from dissociative Li ++ He states and (b) that the two-center pathway strongly dominates over the direct photoionization channel for photon energies close to one of the molecular LiHe resonances.Abstract Photoionization of a weakly bound van-der-Waals dimer, composed of two atomic speciesAandB, is studied theoretically. AtomAcan be ionized either directly or via an indirect two-center channel, where atomBis first resonantly photoexcited and, afterwards, transfers the excitation energy via long-range electron–electron correlations radiationlessly to atomA, causing its ionization. By taking the vibrational nuclear motion of the dimer during the process into account, we analyze the contributions to the photoionization cross section from bound and dissociative molecular states in the final A+ –Bsystem. For the specific example of a LiHe dimer we show (a) that substantial contributions to both ionization mechanisms result from dissociative Li ++ He states and (b) that the two-center pathway strongly dominates over the direct photoionization channel for photon energies close to one of the molecular LiHe resonances.

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Competition of multiphoton ionization pathways in lithium

Balázs István Tóth, Attila Tóth, András Csehi

Abstract We study the three-photon ionization of atomic lithium by intense, short light pulses, via numerically solving the time-dependent Schrödinger equation. Two-photon Rabi oscillations are induced between the 2s and 4s states, which are damped due to single-photon ionization to the p continuum. Developing a minimal three-level model, we analyze the spectral features of the Autler–Townes (AT) doublet that is formed upon the resonant coupling with the laser pulse. Furthermore, we show that this 2 s →→ 4 s → p c o n t i n u u m pathway is the dominant process, if the duration of the laser pulse exceeds a certain value. For shorter pulses, ionization through the 2p state ( 2 s → 2 p → 4 d → f c o n t i n u u m ) gradually becomes the dominant process, provided that the pulse is strong enough to induce several Rabi floppings. Here, we trace the competition of these ionization pathways by observing the structural changes in the shape of the AT doublet.Abstract We study the three-photon ionization of atomic lithium by intense, short light pulses, via numerically solving the time-dependent Schrödinger equation. Two-photon Rabi oscillations are induced between the 2s and 4s states, which are damped due to single-photon ionization to the p continuum. Developing a minimal three-level model, we analyze the spectral features of the Autler–Townes (AT) doublet that is formed upon the resonant coupling with the laser pulse. Furthermore, we show that this 2 s →→ 4 s → p c o n t i n u u m pathway is the dominant process, if the duration of the laser pulse exceeds a certain value. For shorter pulses, ionization through the 2p state ( 2 s → 2 p → 4 d → f c o n t i n u u m ) gradually becomes the dominant process, provided that the pulse is strong enough to induce several Rabi floppings. Here, we trace the competition of these ionization pathways by observing the structural changes in the shape of the AT doublet.

Journal of Physics B Atomic Molecular and Optical PhysicsFeb 21, 202410 citations

{\mathrm{Li}}^{*}(2p)+\mathrm{Li}(2s)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{*}(3d)+\mathrm{Li}(2s),

{\mathrm{Li}}^{*}(3d)+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Li}}^{+}+e.

We report the observation of a two-step radiative collisional ionization between

{\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})

and $\mathrm{Ba}({6s}^{2} ^{1}S_{0})$ in which an optical photon is absorbed simultaneously with the collision, ${\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})+\mathrm{Ba}({6s}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\mathrm{Na}(3s ^{2}S_{\frac{1}{2}})$ and with subsequent photoionization of the excited barium, ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})+\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\rightarrow}{\mathrm{Ba}}^{+}+e$. We observe peak ion intensity close to the difference frequency between ${\mathrm{Ba}}^{*}({6p}^{2} ^{1}S_{0})$ and

{\mathrm{Na}}^{*}(3p ^{2}P_{\frac{3}{2}})

as well as a quadratic increase of ion intensity with laser power. These results confirm, complement, and extend the interpretation of an earlier observation.

The results of double-laser experiments in which

{\mathrm{Na}}_{2}^{+}

and

{\mathrm{Na}}^{+}

are produced in crossed alkali beams under single-collision conditions in the presence of strong optical fields are reported. Structure in the mass-selected product ion intensity as a function laser frequency is observed when the optical field is strongly focused and tuned far off atomic or dimer transitions. These measurements are the first to show that the nuclear motion of the quasimolecular collision intermediate plays an important role in laser-induced collisional ionization.