Strong-field ionization of water: Nuclear dynamics revealed by varying the pulse duration

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 H2O and D2O) 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.

Automated summary

Polyatomic molecules in strong laser fields exhibit substantial nuclear motion within tens of femtoseconds. Short pulses show minimal internuclear motion before shutting off, while rapid motion occurs during double ionization in longer pulses. The results suggest a simple tunnel ionization model can help interpret the observed motion.