Physical Review Letters

Observation of interference between quadrupole and dipole transitions in low-energy (2-eV) photoionization from a sodium Rydberg state

Gerd Leuchs, Stephen J. Smith, S. N. Dixit, P. Lambropoulos

Published Feb 17, 1986• 14 citations

Abstract

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from ${13}^{3}$${\mathrm{D}}_{3/2}$-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.

DOI: 10.1103/physrevlett.56.708

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Physical Review Letters

Observation of interference between quadrupole and dipole transitions in low-energy (2-eV) photoionization from a sodium Rydberg state

Gerd Leuchs, Stephen J. Smith, S. N. Dixit, P. Lambropoulos

Published Feb 17, 1986• 14 citations

Publisher

Abstract

A measurement of the azimuthal dependence of the angular distribution of photoelectrons from

{13}^{3}$${\mathrm{D}}_{3/2}

-state sodium atoms aligned transversely to the direction of propagation of, and parallel to the direction of linear polarization of, 532-nm ionizing laser radiation, is described. The measured distribution is I(\ensuremath{\varphi})=1+0.026(6)cos\ensuremath{\varphi} where \ensuremath{\varphi}=0 is the direction of the laser beam. This departure from the symmetry I(\ensuremath{\varphi})=const predicted for a pure electric dipole transition is represented theoretically as due to a dipole-quadrupole interference term.

DOI: 10.1103/physrevlett.56.708

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{\mathrm{}}^{2}

{D}_{3/2}

and 6d

{\mathrm{}}^{2}

{D}_{5/2}

electric quadrupole transitions and for one-photon resonant, three-photon ionization via the 5d

{\mathrm{}}^{2}

{\mathrm{D}}_{3/2}

and 5d

{\mathrm{}}^{2}

{D}_{5/2}

transitions. The ratios of the total ionization rates for linearly and circularly polarized light have also been measured for the 6d

{\mathrm{}}^{2}

{\mathrm{D}}_{3/2}

and 6d

{\mathrm{}}^{2}

{D}_{5/2}

states. A theoretical analysis and detailed comparison with the experimental results are given.

Sodium atoms are excited to either the

3^{2}P_{\frac{3}{2}}

3^{2}P_{\frac{1}{2}}

state using a linearly polarized dye-laser beam and are subsequently ionized using a linearly polarized nitrogen-laser beam. Angular distributions of the ejected electron have been both measured and calculated for several relative orientations of the photon polarization vectors. The difference between the

s

- and

d

-continuum partial-wave phase shifts ${\ensuremath{\delta}}_{s}\ensuremath{-}{\ensuremath{\delta}}_{d}$ and the ratio of the radial dipole matrix elements (

\frac{{d}_{s}}{{d}_{d}}

) are obtained.

\beta

from its nonrelativistic value of 2. Spin-orbit coupling displaces the minimum in the cross section for excitation to the $\rm \varepsilon P\sb{1/2}$ and $\rm \varepsilon P\sb{3/2}$ and results in a rapid variation of the angular distribution with photon energy in this region. Through the measurement of two-photon ionization angular distributions the quantum defects and spin-orbit coupling were investigated. These studies help us to understand the phase interference interaction, and the data in those studies would be used to analyze the interference processes.

{D}_{3/2}

and 4

{D}_{5/2}

intermediate states. The comparison of the theoretical results with the experimental data also clearly shows that the hyperfine splitting of the ground state has to be taken into account at high laser intensities although the low-intensity angular distributions do not depend on the initial ground hyperfine state.