Areas of Research
It is proving possible to use some of the largest lasers on Earth, and powerful computer models, to address some of the most dramatic events in the universe -- supernovae. We have devised an experiment using the Omega laser in Rochester, NY, to produce structures similar to those driven by the outflow of matter from a supernova explosion. You may have seen it discussed recently in Science, Sky and Telescope, or New Scientist. We produce and observed, in the laboratory, never-before-seen processes that are hypothesized to matter in supernovae and supernova remnants. This image shows data from the first laser experiment to produce a spherically-diverging, hydrodynamically unstable system that is relevant to supernovae
We are also active in the computer simulation of such hydrodynamic effects. We have recently explored (with colleagues from Arizona and Livermore) the impact of an instability known as "Richtmeyer Meshkov" on the structure of supernova remnants. The figure which follows shows three spikes of dense matter that penetrate toward the blast wave from the stellar explosion, in consequence of this process.
Plasma, the fourth state of matter, is an important part of the physical universe and is important for many earthbound applications (see Plasma Science and Technology). These applications have had so much emphasis, however, that the fundamental behavior of plasmas is relatively unexplored by comparison with the behavior of other states of matter. Lasers and laser-produced plasmas offer unique tools for the fundamental study of plasmas. Our understanding of the interaction of an electromagnetic wave with ionized matter is in its infancy, and a laser beam can provide an intense electromagnetic wave for such studies. Our recent studies of stimulated Compton scattering [Drake et al., Physical Review Letters, vol. 64, p.423] and stimulated Raman forward scattering [Batha et al., Physical Review Letters, vol. 66, p.2324 ] are examples of this. Beyond this, the laser provides a powerful diagnostic tool for the study of the plasma itself. We recently used laser-plasma techniques to produce a plasma in which we observed ion plasma waves [Bauer et al., Physical Review Letters , vol. 74, p. 3604], in which, amazingly, the ions oscillate but the electron density doesn't. Likely future topics include the study of acoustic noise, which at the moment is sometimes 5 orders of magnitude larger than it ÒshouldÓ be, strongly-coupled plasmas, in which strong ion-ion interactions alter the plasma behavior, and relativistic plasma physics, in which the electron velocities are relativistic. These basic plasma physics experiments are most likely to take place at the Trident laser at Los Alamos or at the Center for Ultrafast Optical Studies at Michigan.
This image shows the intensity of the laser scattering, per unit wavelength per unit time, seen in experiments to detect the ion plasma wave. The two spectral peaks correspond to oppositely-directed ion plasma waves. One of these is unstable and grows in time.
Intense lasers were first developed for laser fusion research, which remains an active area for us. We work at present with members of the laser fusion program at Trident at Los Alamos and at Omega at Rochester to study laser-plasma interactions that can alter the properties of the laser beams or the distributions of the plasma particles. This can help, or more often hurt, laser fusion. Most often, the interactions involve unstable, driven waves and their saturation. It is important to understand the underlying processes so that laser fusion systems can be built to operate in the optimum regimes. [see Drake et al., Physical Review Letters, vol. 74, p.3157, Watt et al., Physics of Plasmas, vol. 3, p.191, and Drake et al., Physical Review Letters, vol. 77, no. 1] We have done some of the groundbreaking work on several instabilities and on numerous physical problems in this area, and we expect this to continue.