Role of excited states in coherent harmonic bremsstrahlung in a photoionized plasma

It is established for a photoionized plasma formed in the barrier-suppressi on ionization regime that the preliminary population of the excited states of the ionizing atoms plays an important role. It is established that in th is case an anomalously strong (several orders of magnitude) increase occurs in the efficiency of generation of the harmonics of the pump radiation. It is shown that a relative decrease of the harmonics generation efficiency o ccurs with time as a result of collisions of the electrons produced by ioni zation. (C) 2000 MAIK "Nauka/Interperiodica".