The Role of the Prepulse in Cluster Heating by a High-Power Femtosecond Laser Pulse

The interaction of a 60-fs laser pulse with argon clusters was experimentally studied. It is shown that cluster heating by an intense femtosecond pulse preceded by a picosecond prepulse can produce plasma whose ionization state is determined by the prepulse properties, while the mean energy of hot electrons is determined by the main pulse intensity. A simple model of cluster plasma evolution is suggested, allowing an adequate description of its X-ray emission.