ABSTRACT
High-power lasers (see section D10.1) produce plasmas with the highest macroscopic energy density that can be obtained in the laboratory. Such plasmas can also exhibit the highest energy density in the radiation field as well as the most extreme values of other quantities, notably pressure, density, velocity and velocity gradient. Such extreme conditions arise because, at their focus, high-power laser beams produce very high photon energy density. For example, at the focus of the world’s highest intensity laser (1021 W cm−2), the energy density of the laser light is approximately 1012 J cm−3 with the rate of energy delivery 1024 J cm−3 s−1. The same energy density and rate of energy delivery would require heating material and thermal radiation to 20 keV (2 × 108 K) in 1 ps. Although there is inefficiency in transferring energy from monochromatic laser light to thermal energy, the interaction of these laser photons with material results in extreme material conditions. The purpose of this chapter is to look at the plasma conditions that can currently be produced and those conditions that may be achieved through future laser development. In this way we hope to give the reader an appreciation of the opportunities that high-power lasers provide for undertaking experiments to test our understanding of many aspects of physics under extreme conditions. So as to put those conditions in context, we compare, where possible, with values found in astrophysical situations.
