Femtosecond laser interactions with methyl iodide clusters. I. Coulomb explosion at 795 nm

The study of the interaction of femtosecond laser radiation with matter, es pecially clusters, has blossomed in recent years due to advances in laser t echnology. One aspect of this interaction is Coulomb explosion. This effect occurs when the repulsive energy of like charges, known as Coulomb repulsi on, overcomes the cluster's total cohesive energy, causing the cluster to d isintegrate into charged fragments. In this study, the interactions of meth yl iodide clusters, formed in a supersonic expansion using argon and helium as carrier gases, were investigated at 795 nm using a Ti: Sapphire femtose cond laser. The resulting atomic and cluster ions were analyzed in a reflec tion time-of-flight mass spectrometer. The focus of these studies was the e lucidation of the effects of carrier gas and laser wavelength on the laser- cluster interactions leading to Coulomb explosion. To achieve these goals, the effects of different carrier gases, laser power, cluster distribution, and the resulting Coulomb explosion energies were examined. A secondary con sideration was to examine the experimental results with regard to the Coher ent Electron Motion and Ionization Ignition models. (C) 1999 American Insti tute of Physics. [S0021-9606(99)00513-9].