Evidence for Rescattering in Intense, Femtosecond Laser Interactions with a Negative Ion

It is now well established that energetic electron emission, nonsequential ionization, and high harmonic generation, produced during the interaction of intense, femtosecond laser pulses with atoms (and atomic positive ions), can be explained by invoking rescattering of the active electron in the laser field, the so-called rescattering mechanism. In contrast for negative ions, the role of rescattering has not been established experimentally. By irradiating ${\mathrm{F}}^{-}$ ions with ultrashort laser pulses, ${\mathrm{F}}^{+}$ ion yields as a function of intensity for both linearly and circularly polarized light have been measured. We find that, at intensities well below saturation for ${\mathrm{F}}^{+}$ production by sequential ionization, there is a small but significant enhancement in the yield for the case of linearly polarized light, providing the first clear experimental evidence for the existence of the rescattering mechanism in negative ions.

Figure 1

The yield of ${\mathrm{F}}^{+}$ ions from ${\mathrm{F}}^{-}$ as a function of peak laser intensity: (a) experimental data for linearly (solid circles) and circularly (open circles) polarized light; (b), (c) results for linear and circular polarization, respectively, compared with predictions of ADK theory [21] under the same conditions.