Nuclear spin polarization produced by ion-beam-surface-interaction, its optical detection and use in an atomic quantum-beat experiment

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-

Nuclear polarized7Li and14N ions via ion beam surface interaction at grazing incidence

“…This means, however, that the technique of enhancing the transfer of anisotropy from the electronic shell to the nucleus via the application of an "adiabatic magnetic field" as suggested in Ref. [7] cannot be applied. With such a field configuration the transfer from ground configurations is improved, but at the same time the contribution of the excited terms is lost due to the magnetic decoupiing of the nucleus from the electronic shell during the lifetime of the excited terms.…”

“…the quarter-wave plate was rotated in steps of 90 ~ with an angle of odd multiples of 45 ~ between the fast axis of the quarter wave plate and the polarizer axis [1,2,5,7,8]. Since the counting rates were low a proper background correction is important.…”

“…Since high resolution techniques with fast ions need an anisotropic population of atomic states under study, the universal application of IBSIGI for fine and hyperfine (hi) structure measurements is evident [6,7]. Furthermore the high degree of electronic orientation considerably influences the nuclear spin distribution via hf-interaction and enables the IBSIGI technique to produce nuclear spin polarized (oriented) ions; nuclear polarizations of PI = 14 % in 14N (I= 1) and Px = 11% in 13 C (I = 1/2) have been reported [7]. In this paper we continue the former work of production of nuclear spin polarized ions.…”

Capture of polarized electrons into excited terms of fast atoms during grazing surface collisions

“…Then the anisotropy transferred via hf-interaction to the nuclear spin ensembles is enhanced also, and fast beams with considerable nuclear polarization can be expected [3,5].…”

Unified description of circular polarization in supermultiplet lines of ions, excited by beam surface interaction

“…Spectra emitted by Argon in a grazing incidence experiment [4] show only very weak ArIII but intense ArII lines, which means that the capture is favoured in this situation. As the ion surface interaction has recently been demonstrated to give polarized ground states too [19], there is no reason why the mechanism for production of polarization should be effective only in the last capture. Therefore the polarization, which is finally measured, is probably influenced by the multiple loss capture process.…”