We have measured large orientations for Ar n states excited by 300-keV Ar + impact on solid Cu surfaces at grazing incidence. We report circulary polarized light fractions of up to 76% and interpret the excitation mechanism as an orbital-angular-momentum effect. As an application of this new excitation scheme, a zero-field level-crossing experiment is presented.We report new experiments which confirm and extend the recent observation that the excitation of fast ion beams by impact with inclined solid amorphous surfaces can lead to appreciable excited-state orientations. 1 We present measurements of angular distributions of the scattered ion current which support the assumption that near grazing incidence, there is a well-defined direction for the outgoing oriented atoms, as in "tilted-foil" experiments. 2 We also give the first results for the application of this "tilted-surface" effect to atomic level-crossing studies.The experimental setup is shown in Fig. 1. With the axes indicated, the direction of observation was along Ox. The incident beam direction is along Oz, the target surface normal makes an angle a with the -y axis in the yz plane, and we anticipate the results given below by ascribing an angle 9 to the average forward-scattered particle direction. The target was amorphous Cu, of dimensions 30 mmxl5 mmxl mm, and its surface to spectrometer FIG. 1. Experimental setup. The beam cross section is 0.5x 5 mm 2 " was mechanically polished flat to 2 jum. It was mounted on a shaft which was along Ox, and the angle a could be set to a precision of ± 0.17°. A 1-mm-diam pickup wire was mounted parallel to and off center from the x axis in such a way as to describe a circle of radius 7 cm about that axis. The scattered beam current could be measured with this wire as a function of y, in 1.4° steps. The pickup wire and the target could be held independently at variable potentials to suppress secondary-electron emission.The optical system consisted of an achromatic A/4 plate and a linear polarizer, followed by a single imaging lens, a 0.3-m grating spectrometer, and a photo multiplier tube in photon-counting mode. The viewing region was approximately 7 mm in diameter in the yz plane, and was centered on the x axis. Spectra were built up by repetitive sweeping of the wavelength proportional to collected charge of the unbiased target (our results are independent of secondary-electron emission) and recording the photon counts in a synchronized multichannel scaler. Similarly level-crossing curves were obtained by sweeping the magnetic flux B z , proportional to time at less than ± 5% beam fluctuations and recording photons of a particular line and polarization. B z , was applied by Helmholtz coils aligned along the scattered beam direction Oz'.In order to determine excited-state orientations of free scattered ions we measured the normalized Stokes parameter S/I= {la" -Io + )/(Ia" + Ia + ) by rotation of the A/4 plate in steps of 90°, where Jcr" and Ia + are, respectively, right and left circularly polarized light inte...

No abstract

No abstract

No abstract

It is shown that nuclear spin polarized ion beams can be generated by ion beam surface interaction at grazing incidence. An optical detection method for the nuclear polarization after foil excitation of such beams is described and used for a hyperfine structure quantum-beat measurement on the 14N II-2 p 3 p 3D-state.In a recent letter [1] it was shown that large Ar + excited state orientations are obtained by 300 keV Ar § ion beam surface interaction at grazing incidence (IBSIGI). Further studies [2] with different ions than Ar § have shown this to be a general phenomenon based on a strong orbital angular momentum orientation due to the anisotropic Coulomb interaction with the surface. These findings make it worth considering the partial transfer of electronic orientation to atomic nuclei with I + 0 via hyperfine interaction in order to generate nuclear spin polarized ion beams for the use in various fields of physics. In this communication we first give theoretical estimates for the nuclear orientations to be expected after I~N+-and 13C+-IBSIGI. We then describe and use a method of optical detection of the nuclear orientation of 13C+-and ~4N+-beams after reexcitation of these beams by a carbon foil at normal incidence. Finally we make use of such a nuclear spin polarized beam in a quantum beat experiment 1-3] on the hyperfine structure of an excited ~4N+-state. According to Reference 1 the IBSIGI generates an initial oriented orbital angular momentum (-Lx) +0 with the right handed coordinate system used in Fig. 1. In ((LS)JI)F-coupling the partial transfer of orientation from this (-Lx) to the nucleus can then be described in three steps: 1) An isotropic electronic spin S and an isotropic nuclear spin I have to be coupled with this (-Lx) to form the eigenstates of the free ion in the ((LS)JI)FM-base.2) The actual transfer takes place as a function of time after the excitation (orientation) process under the combined influence of the fine-and hyperfine interaction. 3) As a result one obtains after averaging over long times compared to the hyperfine periods an orientation (-Ix) which can be calculated by decoupling the system again to the (LMLSMsIMI)-base in order to evaluate the expectation value (-Ix). We choose for the description of the whole procedure the density matrix with its expansion coefficients p(k) with respect to irreducible tensor operators Tq (k~. Taking the reflection symmetry of the IBSIGI with respect to the y-z plane in Fig. 1 into account and choosing the x-axis as quantization axis, only the components Cp (o~ , Lp(ol) , Lp(02) , La(2) P_+2 "" can occur [4] where the k = 0, 1, 2 components characterize the population (monopole-polarization), the orientation (dipole-polarization) and the alignment (quadrupole-polarization), respectively. Since furthermore without external fields k remains a constant of motion during the whole transfer process, we neglect as an approximation the higher multipole polarization components with k>2 and concentrate for sim-