Electron spin polarisation in laser induced autoionisation

Roberto Buffa, J. K. Spong

P. Thornton Greenland

A simple expression for the ion yield from resonant three-photon ionisation through an autoionising level of a complex atom is obtained. In contrast to some treatments it is assumed that coherent, pulsed lasers of fixed polarisation are used to ionise the atoms, and effects which arise from the coherence are identified. The dependence of ion yield on the laser polarisations is exposed, and the possibility of a spectroscopy based on this dependence is discussed. As an example, it is shown how the spin of the autoionising level in a complex atom may be determined by only relative ionisation measurements.

Грызлова Елена Владимировна, Alexandr I. Magunov, I. Rotter +1 more

The rotating wave approximation is used to obtain parametric expressions for the resonance cross section for the atomic ground state ionisation by linearly polarised probe radiation in the vicinity of an autoionisation state coupled resonantly to another autoionisation state through circularly polarised laser radiation. Calculations are made for the 2s2p 1 P and 2s3d 1 D states of the helium atom. It is shown that the structure of the photoionisation cross-section spectrum formed for circularly polarised laser radiation differs qualitatively from the structure formed in the case of linear polarisation. The dependence of this structure on the intensity and frequency of laser radiation and the direction of polarisation of the probe radiation is studied.

Joseph H. Eberly, Kazimierz Rza̧żewski, Dan Agassi

Guanhua Yao, Zhizhan Xu

Strong laser-field-induced autoionisation in the presence of both photoionising and radiative decay of the autoionising state (AS) is investigated, focusing on the laser intensity dependence of the photoemission and photoelectron spectra. In contrast to previous predictions, power broadening and increasing reduction of the doublet peak heights with field strength are found in the photoemission spectrum. Similar effects leading to considerable suppression and even complete disappearance of the lowest-order peaks in the photoelectron spectrum, together with peak switching, are also demonstrated, which are closely related to above-threshold ionisation. In addition, it is suggested that the total number of energetic photoelectrons may serve as an alternative to measuring the atomic parameters of the AS. All these effects are attributed to the presence of the strong 'probe': laser-induced decay of the AS.

Jakub Zakrzewski