Benchmark Measurements of $\mathbf{H}_3{}^{+}$ Nonlinear Dynamics in Intense Ultrashort Laser Pulses

The $\mathrm{H}_3{}^{+}$ ion is the simplest polyatomic molecule and is destined to play a central role in understanding such molecules in intense ultrashort laser pulses. We present the first measurements of the intense field dissociation and ionization of $\mathrm{D}_3{}^{+}$ using coincidence three-dimensional momentum imaging. Our results show features that are a consequence of this molecule’s unique equilateral triangular geometry, providing a fundamentally new system for theoretical development.

Figure 1

Normalized rates for $\mathrm{D}_3{}^{+}$ fragmentation channels as a function of laser intensity using 7 fs, 790 nm laser pulses. The rates have been normalized to the ion-beam current of $\sim 5\mathrm{nA}$. The error bars show the statistical error of the data. The inset shows cuts of the lowest two potential energy surfaces calculated for $\mathrm{D}_3{}^{2+}$, where $R$ and $r$ are defined by the diagram.

Figure 2

The KER distribution for ${\mathrm{D}}^{+}+{\mathrm{D}}^{+}+{\mathrm{D}}^{+}$ fragmentation following double ionization of $\mathrm{D}_3{}^{+}$ using 7 fs pulses compared to 40 fs at 790 nm, ${10}^{16}\mathrm{W}/{\mathrm{cm}}^2$. The inset shows the KER distribution for ${\mathrm{D}}^{+}+\mathrm{D}_2{}^{+}$ and ${\mathrm{D}}^{+}+{\mathrm{D}}^{+}+\mathrm{D}$ fragmentation following single ionization by the same 7 fs pulses. The error bars show the statistical error of the data.

Figure 3

(a),(b) The alignment $\theta$ of the normal vector to the molecular plane $\widehat{n}$, relative to the laser polarization $\epsilon$; see inset for definitions ($\theta >180°$ is mirrored to complete the polar plot). (a) Double ionization and (b) single ionization, for 7 fs, ${10}^{16}\mathrm{W}/{\mathrm{cm}}^2$ laser pulses. The fits to the data are ${sin}^3\theta$ angular distributions. (c),(d) The orientation $\chi$ of the velocity vector of the ${\mathrm{D}}^{+}$ and D fragments of double and single ionization, respectively, relative to the projection of the laser polarization within the molecular plane (for large fields within the molecular plane, i.e., $60°<\theta <120°$). (c) Double ionization for 7 fs pulses, and (d) single ionization for 7 fs and 40 fs pulses. The error bars show the statistical error of the data.