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

Multiphoton detachment of halogen negative ions with elliptically polarized light

Christophe Blondel, F. Dulieu, Christian Delsart

Published May 6, 1996• 0 citations
Publisher

Abstract

Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can be reached by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the whole set of data with an analytic formula. We give here the appropriate formula, valid for any number N of exciting photons, with the assumptions of (1) an initially even and momentumless (J equals 0) atom or ion and (2) that after excitation of an electron, the residual core be left in an odd state. These are the conditions met by multiphoton detachment from halogen negative ions. With elliptically polarized light of (lambda) equals 1064.2 nm, we have measured the angular distributions of three-photon detached electrons from the ion I-, and four-photon detached electrons from Cl- and F-. The experimental results are quantitatively analyzed and commented on.

DOI
10.1117/12.239750

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Multiphoton angular distributions with elliptically polarized light. I. Analytic ellipticity dependence of photoelectron distributions in the polarization plane

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Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can only be reached, however, by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the data with a common formula. But the analytic dependence of photoelectron angular distributions on the ellipticity has been unknown up to now, except for the one- and two-photon excitation cases. Here we give a demonstration of a general formula, valid for any number N of exciting photons, with the assumptions of (i) an initially even and momentumless (J=0) atom or ion and (ii) that after excitation of an electron, the residual core is left in an odd state. Slight modifications in the demonstration would make it possible to extend the general formula to any J=0 initial atomic state.

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Multiphoton transitions. III. Rates of multi-photodetachment of negative ions

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arXiv:1808.01860•Physical Review Letters•Jul 30, 2018•30 citations
Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can be reached by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the whole set of data with an analytic formula. We give here the appropriate formula, valid for any number N of exciting photons, with the assumptions of (1) an initially even and momentumless (J equals 0) atom or ion and (2) that after excitation of an electron, the residual core be left in an odd state. These are the conditions met by multiphoton detachment from halogen negative ions. With elliptically polarized light of (lambda) equals 1064.2 nm, we have measured the angular distributions of three-photon detached electrons from the ion I-, and four-photon detached electrons from Cl- and F-. The experimental results are quantitatively analyzed and commented on.
Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can only be reached, however, by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the data with a common formula. But the analytic dependence of photoelectron angular distributions on the ellipticity has been unknown up to now, except for the one- and two-photon excitation cases. Here we give a demonstration of a general formula, valid for any number N of exciting photons, with the assumptions of (i) an initially even and momentumless (J=0) atom or ion and (ii) that after excitation of an electron, the residual core is left in an odd state. Slight modifications in the demonstration would make it possible to extend the general formula to any J=0 initial atomic state.
We report in detail our complete characterization of atomic photoionization via a single measurement, namely, that of the two-photon photoelectron angular distribution using elliptically polarized light. Through these measurements we are able to determine the atomic parameters necessary to unambiguously describe two-photon ionization of atomic rubidium. These parameters include relative cross sections for photoionization into various outgoing channels as well as the phase difference between the continuum S and D partial waves. We present a derivation of the angular distribution with arbitrarily polarized light in terms of these cross sections and phases, demonstrate the advantages of using elliptically polarized light, discuss details of the experiment, and report the results of our measurements in this paper. While measured phase differences are in excellent agreement with expected values over the entire range of photoelectron kinetic energy of our measurements from 0 to 0.5 eV, ratios of cross sections for photoionization into the two D channels are anomalous, suggesting unexpected fine structure effects in these continua.
Ce travail etudie deux aspects du photodetachement des ions negatifs d'halogenes. L'etude experimentale du detachement multiphotonique d'ions negatifs d'halogenes dans le cas general de la polarisation elliptique a ete completee par la mesure des distributions angulaires de l'iode negatif detache par trois photons, et du chlore et fluor negatifs detaches par 4 photons (1064 nm chaque fois). La conservation de la symetrie par rapport au sens de parcours de l'ellipse dans ces distributions, contrairement a ce qu'on attendait, constitue le resultat experimental le plus marquant. Pour analyser ces mesures, une extension du theoreme de yang a ete etablie. Elle donne la forme mathematique des distributions angulaires de photoelectrons detaches par n photons issus d'un systeme atomique ayant un moment cinetique total nul et dont le cur est laisse dans un etat impair, dans le cas general de la polarisation elliptique. Une etude numerique du signal de detachement du fluor negatif detache par 3, 4 et 5 photons a ete realisee. Elle prend en compte le phenomene de competition de voies de photodetachement et l'effet ponderomoteur. Le second aspect de ce travail concerne la construction d'une experience dite de microscopie de photodetachement. Son principe, jusqu'alors jamais mis en pratique, est le suivant: un electron detache dans un champ electrique peut atteindre le detecteur par deux chemins possibles, on peut donc observer des interferences electroniques. On peut interpreter ces interferences comme une coupe radiale de fonction d'onde de photodetachement. L'etude de la faisabilite, la description de l'experience, ainsi que les premieres images obtenues avec le brome negatif sont presentees. On verifie que les resultats experimentaux sont en accord avec la theorie semi-classique
The aim of this thesis is to extend the study of multiphoton processes to the heavier negative ions of the alkali-metal atoms and thus, Na"- and K"- were natural candidates for this investigation. The main idea is to achieve an homogeneous description of negative alkaline ions and their response to an intense laser field. This idea has been suggested by recent experimental findings for negative alkaline ions which have revealed a rich structure of their scattering and photodetachment spectra, showing the existence of high-lying temporary negative ion states. Moreover, dramatic effects due to excess photon detachment have been observed yielding additional information on the dynamics of these highly correlated systems
Elliptical dichroism is known in atomic photoionization as the difference in the photoelectron angular distributions produced in nonlinear ionization of atoms by left- and right-handed elliptically polarized light. We theoretically demonstrate that the maximum dichroism |Δ_{ED}|=1 always appears in two-photon ionization of any atom if the photon energy is tuned in so that the electron emission is dominantly determined by two intermediate resonances. We propose the two-photon ionization of atomic helium in order to demonstrate this remarkable phenomenon. The maximum elliptical dichroism could be used as a sensitive tool for analyzing the polarization state of photon beams produced by free-electron lasers.