Studies of ion energy and yield fromargon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecondlaser pulses with argon clusters has been studied by measuring the energyand yield of emitted ions. With two different supersonic nozzles, thedependence of average ion energy on cluster size in a large range of has been measured. The experimental results indicate thatwhen the cluster size , the average ionenergy Coulomb explosion is thedominant expansion mechanism. Beyond this size, the average ion energy getssaturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamicexpansion behavior. We also find that with the increasing gas backingpressure, there is a maximum ion yield, the ion yield decreases as the gasbacking pressure is further increased.