Dependence of Rydberg-state creation by strong-field ionization on laser intensity

We investigate numerically and analytically the intensity dependence of the fraction of electrons that end up in a Rydberg state after strong-field ionization with linearly polarized light. We find that including the intensity dependent distribution of ionization times and nonadiabatic effects leads to a better understanding of experimental results. Furthermore, we observe using classical trajectory Monte Carlo simulations that the intensity dependence of the Rydberg yield changes with wavelength and that the previously observed power-law dependence breaks down at longer wavelengths. Our work suggests that Rydberg yield measurements can be used as an independent test for nonadiabaticity in strong-field ionization.

Figure 1

Rydberg yield for the parameters found in [4]: $I=1.4\times {10}^{14}–{10}^{15}$, FWHM of pulse envelope $=30$ fs, $\lambda =800$ nm, and He atom with $I_p=0.9$. The experimental yield (blue dot) was extracted from [4]. The adiabatic CTMC simulation (red diamond) was done using the ADK distribution [36, 37] and the nonadiabatic simulation (green square) is based on [40]. The power law used for fitting is described by $N^{*}/N=a·I^b$ with $b$ given in the legend. The fitting results are represented by lines. Note that the lower absolute values of the experimental yields are due to the decay of the excited states which is not accounted for here (for details see [4]). As the correction factor between TDSE simulations and experimental data in [4] is found to be independent of the laser intensity, this correction factor affects only the prefactor of the power law, but not the power-law exponent we are interested in here.

Figure 2

$f\left(\gamma \right)$ we find in [43] and $c_y\left(\gamma \right)$ as given in [40] with the respective power-law fits in the $\gamma$ regime defined by the parameters listed in Fig. 1.

Figure 3

Intensity dependent Rydberg yield at $\lambda =1200\mathrm{nm}$ (all other parameters are chosen as listed in Fig. 1). Purple dashed line: the adiabatic power law with $b=-1$ [see Eq. (9)]. Red diamonds: adiabatic CTMC simulation data with power-law fit (orange line) to it. Blue dashed-dotted line: estimation by solving Eqs. (14) and (16) exactly, Green dotted line: approximation given by Eq. (C8).

Figure 4

Power-law fit ($a{F}_0^b$ with fitting parameters $a$ and $b$) to the intensity dependence of the standard deviation obtained by Gaussian fits to the histograms of the starting velocities $v_y$ and $v_{\varphi }$ and of the FWHM of the $v_{\perp }$ histogram for the parameters listed in Fig. 1.