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Title: Potential-barrier effects in three-photon-ionization processes

Authors:
;
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1179649
Grant/Contract Number:
FG03-96ER14646
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review A
Additional Journal Information:
Journal Volume: 90; Journal Issue: 2; Journal ID: ISSN 1050-2947
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Pi, Liang-Wen, and Starace, Anthony F. Potential-barrier effects in three-photon-ionization processes. United States: N. p., 2014. Web. doi:10.1103/PhysRevA.90.023403.
Pi, Liang-Wen, & Starace, Anthony F. Potential-barrier effects in three-photon-ionization processes. United States. doi:10.1103/PhysRevA.90.023403.
Pi, Liang-Wen, and Starace, Anthony F. Mon . "Potential-barrier effects in three-photon-ionization processes". United States. doi:10.1103/PhysRevA.90.023403.
@article{osti_1179649,
title = {Potential-barrier effects in three-photon-ionization processes},
author = {Pi, Liang-Wen and Starace, Anthony F.},
abstractNote = {},
doi = {10.1103/PhysRevA.90.023403},
journal = {Physical Review A},
number = 2,
volume = 90,
place = {United States},
year = {Mon Aug 04 00:00:00 EDT 2014},
month = {Mon Aug 04 00:00:00 EDT 2014}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1103/PhysRevA.90.023403

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  • Potential barriers in the effective radial potential experienced by a photoexcited electron are shown to result in dramatic, resonancelike effects in two-photon ionization processes. In a two-photon ionization process, such potential barriers may affect not only the final state of the electron (as in ordinary photoionization), but also the intermediate-state electron wave packet corresponding to the absorption of one photon. We illustrate these effects for the generalized two-photon cross sections for ionization of Ar and Xe within a single-active-electron, central-potential model.
  • We consider effects which occur when four-wave sum frequency generation and multiphoton ionization are induced by lasers tuned near a three-photon resonance and simultaneously near or at a dipole allowed four-photon resonance. In studies with unfocused laser beams, if the phase mismatch of the generated four-wave-mixing field is large and the related two-photon resonance for the absorption of a four-wave-mixing photon and a laser photon results in strong absorption of the four-wave-mixing field, a coherent cancellation occurs between the pumping of the resonance by two- and four-photon processes. This interference effect occurs when the first laser is tuned on eithermore » side of the three-photon resonance and {vert bar}{Delta}{ital k}{sub {ital r}L}{vert bar}{much gt}1, where {Delta}{ital k}{sub {ital r}} is the mismatch and {ital L} is the length of the path of the laser beams in the gas. With focused laser beams large differences occur between ionization with unidirectional beams and with counterpropagating laser beams when {vert bar}{Delta}{ital k}{sub {ital r}b}{vert bar}{much gt}1, where {ital b} is the confocal parameter of the focused laser beams. Strong absorption of the four-wave-mixing field is shown not to be necessary for strong destructive interference with focused laser beams when the phase mismatch is large. This work also suggests an explanation for earlier experiments where the presence of a four-photon resonance enabled the generation of third-harmonic light in a positively dispersive wavelength region. We argue that this process can occur when the laser used to achieve the four-photon resonance is focused on the small {ital z} ({ital z} is the coordinate in the direction of propagation) side of the focal point of the laser responsible for the third-harmonic generation.« less
  • Three-photon resonance enhancement of third-harmonic generation and multiphoton ionization is treated for a slab geometry configuration. Striking pressure effects which become important at concentrations n> or approx. =10/sup 12//cm/sup 3/ for narrow-bandwidth short-pulse lasers are predicted for both the third-harmonic signal and the multiphoton ionization. For example, part of the third-harmonic signal exits the slab simultaneously with the laser pulse while another part is time delayed for small detunings from resonance. At intermediate detuning from the three-photon resonance the two parts can interfere. Multiphoton ionization yields near three-photon resonance are strongly suppressed under certain conditions, and peaks may occur formore » proper detunings on both sides of the three-photon resonance. A detailed experimental verification is suggested for Xe.« less
  • To clarify the ionization mechanism of large molecules under multi-photon ionization conditions, photo-electron spectroscopic studies on anthracene have been performed with electron imaging technique. Electron kinetic energy distributions below a few eV reveal that three kinds of ionization channels coexist, viz., vertical ionization, ionization from Rydberg states, and thermionic hot electron emission. Their relative yield is determined by the characteristic of the laser pulse. The duration in particular influences the ratio between the first two processes, while for higher intensities the last process dominates. Our results provide strong evidence that internal conversion plays an important role for the ionization ofmore » the molecule.« less
  • Energy-resolved photoelectron angular distributions have been measured for the nd /sup 2/D states (n = 11--23) in cesium and rubidium atoms for two-photon resonant, three-photon ionization under conditions where the spin-orbit fine structure was not resolved. The photoelectron angular distributions reveal strong fine-structure mixing effects when the time duration of the laser pulse is longer than the time corresponding to the inverse of the fine-structure splitting of the nd states involved. Three-photon ionization photoelectron angular distributions for sodium atoms have been studied both experimentally and theoretically for laser frequencies in which resonance enhancement occurs via the two-photon excited nd /supmore » 2/D states (n = 5--9). The laser pulse duration is approx.6 ns which is comparable to or less than the fine-structure mixing time for the unperturbed fine-structure nd /sup 2/D/sub 5/2,3/2/ levels. In addition, the high laser powers approx. 10/sup 8/ W/cm/sup 2/ employed result in alterations of the energy separations of the fine-structure levels (and cause corresponding changes in the mixing times) due to the ac Stark effect. A detailed theoretical analysis is presented and good agreement is obtained with the experimental results.« less