Analysis is made of the relative contributions of the main electronic emission processes (like thermoionic, multiphoton, and field effects), to the production of very high electron density by an ultrashort (fs range), visible or IR, laser pulse on a metallic photocathode. At such a duration, temporal variations of electrons and lattice temperatures have to be considered separately. They can be calculated with Anisimov's coupled equations, assuming from local thermal equilibrium of electron and photon gas respectively, but this condition is far from being satisfied. The authors establish a relationship between the extracted electronic charge, the incident laser fluence, and the laser pulse duration proving that ultrashort laser pulses are more efficient for the production of a very high photocurrent density with no surface damage.