Strong Field Ionization of Water: Nuclear Dynamics Revealed by Varying the Pulse Duration

TL;DR

This study compares how water molecules ionize and dissociate under ultra-short laser pulses of 10 fs and 40 fs, revealing the influence of pulse duration on nuclear motion during strong-field ionization.

Contribution

It demonstrates how pulse duration affects nuclear dynamics in water during strong-field ionization, bridging experimental observations with tunnel ionization theory.

Findings

10-fs pulses prevent significant nuclear motion before ionization

40-fs pulses allow rapid internuclear motion during ionization

Short-pulse data aligns with tunnel ionization predictions

Abstract

Polyatomic molecules in strong laser fields can undergo substantial nuclear motion within tens of femtoseconds. Ion imaging methods based on dissociation or Coulomb explosion therefore have difficulty faithfully recording the geometry dependence of the field ionization that initiates the dissociation process. Here we compare the strong-field double ionization and subsequent dissociation of water (both H$_2$O and D$_2$O) in 10-fs and 40-fs 800-nm laser pulses. We find that 10-fs pulses turn off before substantial internuclear motion occurs, whereas rapid internuclear motion can take place during the double ionization process for 40-fs pulses. The short-pulse measurements are consistent with a simple tunnel ionization picture, whose predictions help interpret the motion observed in the long-pulse measurements.