Mott scattering

Abstract. We address the question of the importance of relativity in selected non-linear radiative processes to be observed when an atomic system is submitted to an intense radiation field. To this end, we report on recent results obtained in the theoretical analysis of the following processes i) two-photon transitions in high-Z hydrogenic systems, ii) laser-assisted Mott scattering of fast electrons, and iii) two-colour photoionisation spectra of atoms in the simultaneous presence of two ultra-intense laser fields. In each case, the signature of relativistic effects is evidenced. 

In these relations the interest lies in the spin-polarization vector of the photoelectron itself, i.e., the detector response Q is assumed to be always perfect, Qt= +1. The same procedure applies if the response of an actual detector with Q, < 1 to polarized electrons is calculated (see below where, for the case of Mott scattering, Q, has to be identified with the Sherman function Ss). 

This expression says that the interaction energy is due to the spin-orbit interaction which, therefore, is responsible for the spin-dependent effect in Mott scattering. The energy of the spin-orbit interaction adds to the potential of the Coulomb... 

In order to measure P by spin-dependent Mott scattering, the incident electron has to be accelerated to 120 keV, scattered on a gold foil, and the backscattered intensities at +120°, called /( left) and /( right), have to be recorded. This gives the signals... 

Spin analysis was carried out by a Mott-scattering detector with a spherically symmetric acceleration field operated at typically 70 keV without retarding potentials [3]. Surface barrier detectors were used as electron detectors. The figure of merit x ///q amounts to about 2.4 x 10 ". The advantages of this type of... 

Mott scattering is a very inefficient means of electron detection and so magnetic contrast SEMPA images wiU require much longer acquisition times. 

The Mott scattering process is extremely inefficient resulting in count rates for SPUPS that are 4—5 orders of magnitude less than in equivalent UPS spectra. The low count-rate means that the technique is generally restricted to use with extremely intense photon sources such as synchrotrons and also generally results in lower resolutions than are achievable in conventional UPS. The spatial resolution is normally of the order of 100 gm and the energy resolution is normally of the order of 0.1 eV. 

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