Free-free experiments: angular distributions of elastic and inelastic electron-helium scattering

Free-free experiments investigate the emission and absorption of radiation during the collision of charged particles with atoms and molecules in a laser field. This process has been well described by the semi-classical Kroll-Watson approximation (KWA).2 In this work, we extend our previous tests of the KWA3 by measuring relative differ- ential cross sections for 350 eV electrons scattered both elastically and inelastically from He targets in the presence of a 1.17 eV laser field at various scattering angles up to 90?. Here, the energy loss of the inelas-

tic processes corresponds to the unresolved lowest excited 1s2l states; the KWA predicts slightly different angular distributions for the elastic and inelastic-scattering cases. We found fairly good agreement between our experiments and the KWA, but the statistics were not sufficient to unambiguously confirm the differences predicted by the KWA. Experiments to improve the statistics are continuing.

1This work was supported by the National Science Foundation under grant No. PHY-2010102 (NLSM)

2N. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804-809 (1973)

3N. L. S. Martin et al., J. Phys. B 51, 134003 (2018), Phys. Rev. A 99,

032708 (2019)