Multiple ionization and Coulomb explosion of mercury clusters in femtosecond laser fields.

We report on studies of multiple ionization and fragmentation of free Hg ( n ≤ 80) clusters in the femtosecond time domain at wavelengths ranging from 255 nm to 800 nm. After excitation by single laser pulses of an intensity of 5 * 10 W/cm we observe prompt formation of multiply charged Hg clusters. The Hg cluster size distribution observed up to n ≈ 80 shows in additon to singly charged also doubly and triply charged clusters with a surprisingly high amount of doubly charged clusters. The measured cluster size distribution is nearly independent of laser wavelengths. For higher laser intensities (2 * 10 W/cm) we observe multiply charged mercury atoms up to Hg. At 10 W/cm molecules and clusters eventually disappear due to Coulomb explosion and complete Fragmentation. Only atomic ions, singly and multiply charged, with high kinetic energies are then observed. [ABSTRACT FROM AUTHOR]