Gauge dependence of the strong-field approximation: Theory vs. experiment for photodetachment of F−

The dependence of the strong-field approximation on the gauge used for the description of the driving laser field is reviewed in connection with the choice of the initial bound state of the unperturbed atom or ion. Electron energy spectra are calculated for the various combinations of gauge and wave function and compared with experimental data for photodetachment of F− by a circularly polarized laser field [B. Bergues, Y. Ni, H. Helm, I. Yu. Kiyan, Phys. Rev. Lett. 95 (2005) 263002]. If the laser intensity is considered a fitting parameter, then our length-gauge results reproduce the experimental results very well. In contrast, in velocity gauge no satisfactory fit can be obtained for any intensity.