Femtosecond laser ablation from wide bandgap crystals (Al2O3, NaCl, BaF2) is studied at intensities between 10(11) and 10(13) W/cm(2), well below the single shot damage threshold. Negative ions an detected at considerable delay and appear to result from thermal desorption. Explosive emission of positive ions and clusters is preceded by strong electron emission. Ionisation occurs via defect enhanced multiphoton absorption. Our results favour the model of Coulomb explosion over that of Phase explosion as the origin of fast ion desorption.