Multiphoton Above Threshold Effects in Strong-Field Fragmentation

We present a study of multiphoton dissociative ionization from molecules. By solving the time-dependent Schrödinger equation for ${\mathrm{H}}_2^{+}$ and projecting the solution onto double continuum scattering states, we observe the correlated electron-nuclear ionization dynamics in detail. We show—for the first time—how multiphoton structure prevails as long as one accounts for the energies of all the fragments. Our current work provides a new avenue to analyze strong-field fragmentation that leads to a deeper understanding of the correlated molecular dynamics.

Figure 1

JES from Eq. (6) for ${\mathrm{H}}_2^{+}$ exposed to a 400 nm, $8.8\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$ laser pulse starting from (a) $v=0$, (b) $v=2$, (c) $v=7$, and (d) $v=9$. The thick black curves in the top and side panels show the ATI and KER spectra, respectively, from integration of the JES. For comparison, frozen nuclei and reflection results (see text) are shown with thin gray lines.

Figure 2

The JES from Eq. (6) starting from $v=9$ at $5.6\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$ as a function of wavelength: (a) 650 nm, (b) 506 nm, (c) 400 nm, and (d) 363 nm.

Figure 3

(a) The total energy $E=E_{\mathrm{N}}+E_e$) spectra for the JES in Fig. 1. (b) Cuts of the JES from Fig. 1c demonstrate the energy sharing between the electron and nuclei starting from $v=7$ for 7- ($E=0.3\mathrm{a}.\mathrm{u}.$), 8- ($E=0.4\mathrm{a}.\mathrm{u}.$), and 9-photon ($E=0.5\mathrm{a}.\mathrm{u}.$) absorption.

Figure 4

Dressed bound and ionization threshold potentials at 400 nm for our 1D ${\mathrm{H}}_2^{+}$ model. The horizontal lines indicate the energies of the states $v=0$, 2, 7, and 9.