Intense Laser Interaction with Noble Gas Clusters

Abstract

The interaction of intense short-laser pulses with atomic clusters has become an important area of research, particularly for understanding the physics of laser-generated plasmas [1]. Clusters are small particles of condensed matter, with sizes ranging from 10 to 10 atoms. As such, they are intermediate to macroscopic condensed matter and microscopic systems, such as atoms and molecules. Intense laser–cluster interaction creates small-scale plasmas (nanoplasmas). While these nanoplasmas are transient, because the clusters eventually explode, they nevertheless allow the investigation of fundamental laser–matter interaction processes such as ionization and laser energy absorption mechanisms. Since cluster sizes can span the transition region between microscopic and macroscopic systems, these processes can be investigated as a function of system size. Interest in laser-induced cluster explosion was sparked by the experimental observation [2, 3, 4, 5, 6, 7] that highly charged, highly energetic ions are created during the interaction of intense lasers with noble gas clusters. The charge state and energy of these ions considerably exceeds those resulting from single-atom experiments with comparable laser intensities. While the average particle density in cluster experiments (10 cm ) is not much higher than in conventional atomic gas density experiments, the local density inside the clusters, 10 10 cm , is close to solid state. Thus cluster beams are near-transparent to laser light, yet they absorb laser energy very efficiently [8], combining the advantages of both atomic gas and solid density targets. This efficient energy absorption has now been confirmed by a wealth of experiments for a broad set of laser parameters, including wavelengths ranging from 100 nm to 1 mm, intensities ranging from 10 to 10 W=cm, and pulse durations ranging from 30 fs to 0.5 ps. To date, most experiments were performed in the near-infrared, corresponding to the Ti:sapphire laser wavelength