Three-body fragmentation of doubly ionized argon trimers in two-color femtosecond laser pulses

Using linearly polarized two-color femtosecond laser fields and coincidence measurements, we experimentally study the three-body fragmentation of the argon trimer following double ionization, resulting in two ionic fragments, $\mathrm{A}{\mathrm{r}}^{+}$, and one neutral fragment, Ar. This three-body channel is distinguished from the raw data by analyzing the correlation between the sum momentum vectors of the two ionic fragments $\mathrm{A}{\mathrm{r}}^{+}$ versus their total kinetic energy releases. Two distinct fragmentation pathways, concerted and sequential, are confirmed by a detailed examination of the kinetic energy releases' correlation spectra, Newton diagrams, and Dalitz plots of the fragments. The emission directions of the neutral fragments from the sequential pathway are manipulated by adjusting the relative phase of the two-color laser fields. The observed relative phase-dependent asymmetry patterns are attributed to the enhanced ionization induced asymmetric emission of residual $\mathrm{A}{{\mathrm{r}}_{2}}^{+}$ in the first dissociation step. Our findings offer valuable insights into the dissociative ionization of argon trimers and are expected to stimulate further research into the ultrafast dynamics of clusters in femtosecond laser fields.