Precise and Accurate Measurements of Strong-Field Photoionization and a Transferable Laser Intensity Calibration Standard

Ionization of atoms and molecules in strong laser fields is a fundamental process in many fields of research, especially in the emerging field of attosecond science. So far, demonstrably accurate data have only been acquired for atomic hydrogen (H), a species that is accessible to few investigators. Here, we present measurements of the ionization yield for argon, krypton, and xenon with percent-level accuracy, calibrated using H, in a laser regime widely used in attosecond science. We derive a transferable calibration standard for laser peak intensity, accurate to 1.3%, that is based on a simple reference curve. In addition, our measurements provide a much needed benchmark for testing models of ionization in noble-gas atoms, such as the widely employed single-active electron approximation.

Figure 1

(a) Experimental data for ${\mathrm{H}}^{+}$ yield (solid circles) compared with theoretical predictions from 3D TDSE (dot-dashed line), standard ADK (dashed line), and empirically corrected ADK (Emp-ADK) (dotted line) models. In some cases, the error bars on the data are smaller than the symbols; see Supplemental Material [19] for error estimates. (b) Percentage difference of experimental ${\mathrm{H}}^{+}$ yield data and both ADK theories from the 3D TDSE simulations.

Figure 2

Top row: Intensity-calibrated experimental data (black circles) for (a) ${\mathrm{Ar}}^{+}$, (b) ${\mathrm{Kr}}^{+}$, and (c) ${\mathrm{Xe}}^{+}$ compared with theoretical predictions from 3D TDSE (blue dot-dashed line), ADK (red dashed line), and Emp-ADK (green dotted line) models, as well as the phenomenological model given by Eq. (3) (cyan solid line). The only fit parameter is the overall rescaling of yield $A$. In some cases, the error bars on the data are smaller than the symbols. Bottom row: Normalized residuals for (d) ${\mathrm{Ar}}^{+}$, (e) ${\mathrm{Kr}}^{+}$, and (f) ${\mathrm{Xe}}^{+}$, for each theoretical prediction, shown as percentage deviations from the experimental yield data for the respective gas targets. Dashed black line indicates barrier-suppression threshold (Xe threshold off scale at $9\times 10^{13}\mathrm{W}/{\mathrm{cm}}^2$).