Resonant Vacuum-Ultraviolet Photoelectron Spectra of Aligned Li Atoms

Abstract

A new method is described in which Li atoms are excited and aligned by pumping of the Li \s 2 2s 2 S\/2-+ \s 2 2p 2 P 1/2,3/2 transitions with a linearly polarized dye-laser beam, and subsequently raised to core-excited \snln'l' 2 S, 2 P, 2 D states by linearly polarized synchrotron radiation. The intensity of the electrons ejected upon the Li \snln'l' 2 S, 2 D-+ Is 2 l Soel autoionization strongly varied with the character of the core-excited state, the intermediate 2 P\/i or 2 Psn state, and the angle between the polarization vectors of the two photon beams.PACS numbers: 32.80.Rm, 32.80.DzVacuum-ultraviolet (VUV) photoelectron spectroscopy has proven an ideal tool for studying the manyelectron dynamics of core-excited atoms. { By the combining of high-power tunable lasers with synchrotron radiation, a new field has been opened. 2 " 4 States optically inaccessible from the ground state can be reached and the ionization of excited states can be investigated. To exploit the full power of the method, we transferred the techniques developed in two-photon laser ionization 5,6 to the VUV regime. The intensity and angular distribution of the outgoing photoelectrons critically depends on the character of the core-excited state, on the alignment of the intermediate state prepared by the laser, and on the relative orientation of the polarization vectors of the two EleVl 6667 6^2 61 06 P: 539 1 85 0-00 i SR Excitation Laserj i i L} r r 1s2p 3 P L = 0.1.2 AutoionizationK 1s2s 3 S 1S 21 S0 l^vl 1s 2 2s 2 S, 3/2 FIG. 1. Schematic energy-level diagram for the Li evenparity core-excited states reached by two-photon (laser plus synchrotron radiation) excitation.radiation fields. Therefore, two-photon ionization can be used as a very sensitive probe to study the excited states of atoms. The three-electron atom Li is an excellent model system to test this new method for core-excited states. The excitation and decay channels are displayed in Fig. 1. Our results are compared with the Kabsorption spectrum of Li* ls 2 2p by Mcllrath and Lucatorto, 7 and with the assignments based on theoretical calculations. 8,9 The experimental arrangement is schematically depicted in Fig. 2. The Li atoms were prepared in an atomic beam emanating from a resistively heated stainless-steel oven. The oven was operated at 400 °C to produce a density of about 10 10 Li atoms/cm 3 in the interaction zone. The 0.6-W linearly polarized beam of a cw-ring-dye laser induced either the transition 2s 2 S\/2 Synchrotron Radiation Cold trap / Electron trajectory Spectrometer axis -CMA-Entrance slit Magic angle (54/7°) Laser radiation Polarization axis FIG. 2. Scheme of the experimental arrangement. The main axis of the polarization ellipse of the synchrotron radiation defines the z axis. The entrance slit of the cylindrical-mirror analyzer, aligned along the z axis, is schematically depicted. The synchrotron radiation propagates in the y direction, and the laser beam in the opposite direction. Both photon beams intersect the atomic Li beam propagating in the x direc...

Coherence and correlations in photoinduced Auger and fluorescence cascades in atoms

“…In this case, it is more appropriate to speak about excitation of autoionizing resonances. First measurements of the electron spectra and angular distributions of the autoionization electrons after the photoexcitation by synchrotron radiation from polarized targets were realized for Li, Na, and Ca atoms, prepared in the first aligned excited states by the laser optical pumping: Li 1s 2 2p (Meyer et al, 1987;Pahler et al, 1992), Na 2p 6 3p (Baier et al, 1994a, b), Ca 3p 6 4s4p Wedowski et al, 1995Wedowski et al, , 1997. Typical geometries of the set-ups used in experiments on the photoionization of laser-prepared atoms are shown in Fig.…”

Combination of lasers and synchrotron radiation in studies of atomic photoionization

“…changes of the relative intensities under the change of polarization. The first observation of this polarization dependence was obtained when recording the Li 1snln 0 l 0 2 S, 2 P and 2 D resonances after laser-excitation to the Li*1s 2 2p 2 P 3/2 state [23]. The relative intensities of these resonances change strongly depending on the relative orientation of the linear polarization vector of the laser with respect to that of the SR.…”

Two-color visible/vacuum ultraviolet photoelectron imaging dynamics of Br2

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