TWIN PEAK DISTRIBUTION OF ELECTRON-EMISSION PROFILE AND IMPACT IONIZATION OF AMBIENT MOLECULES DURING LASER-ABLATION OF SILVER TARGET

Laser-induced plasma generated from a silver target under partial vacu um conditions using the fundamental output of nanosecond duration from a pulsed Nd:yttrium aluminum garnet laser is studied using a Langmuir probe. The time of flight measurements show a clear twin peak distrib ution in the temporal profile of electron emission. The first peak has almost the same duration as the laser pulse while the second lasts fo r several microseconds. The prompt electrons are energetic enough (app roximate to 60 eV) to ionize the ambient gas molecules or atoms. The u se of prompt electron pulses as sources for electron impact excitation is demonstrated by taking nitrogen, carbon dioxide, and argon as ambi ent gases. (C) 1998 American Institute of Physics.