A theoretical model has been developed to simulate plasma formation and evolution during the early stage of picosecond laser ablation of solids. Surface electron emission was implemented as one boundary condition for plasma development above the target. The simulation results indicate that a plasma forms, with electron density on the order of 1020 cm−3, during the picosecond laser pulse. Laser induced gas breakdown assisted by electron emission from the target was found to be the origin of the plasma. In agreement with experimental measurements, longitudinal movement of the electrons inside the plasma was suppressed after the laser pulse. The suppression of the plasma can be attributed to the development of a strong electric field above the target. © 2000 American Institute of Physics.