Soft X-ray emission from small-sized Ar clusters heated by intense, femtosecond laser pulses

摘要

Summary form only given. The interaction of high intensity, ultrashort laser pulses with atomic clusters has been extensively investigated in the past few years. The main characteristic of gaseous cluster is the near-solid-density inside the cluster which results in an enhanced absorption of laser energy via collisional processes and consequently in an increase of X-ray conversion efficiency. The short (subpicosecond) pulse duration of a driving laser is essential for an efficient transfer of laser energy into plasma electrons on a time scale shorter than the disassembly time of the cluster. Previous studies pointed out the importance of spherical resonance absorption for efficient deposition of laser energy into clusters. When using an ultrashort pulse (>50 fs), however, resonance absorption is expected to be marginal since by the time it takes for the over-dense cluster plasma to reach the resonance condition n/sub e/=3n/sub c/ (n/sub e/ is the electron density and n/sub c/ is the critical density), the heating laser pulse is past. Nonetheless even in this case the interaction of ultrashort laser pulse with a near-solid-density cluster can still be efficient due to collisional processes.