A review of low-density porous target materials for laser plasma experiments

Recent high-power laser technologies are creating potential for new aspects of laser acceleration and compact quantum beam sources with controlled targets. Low-density porous materials, commonly known as foams, are promising as high-efficiency targets for laser plasma experiments that create states of matter at high-energy density. Foam fabrication includes a wide range of material chemistry, yet it has not been the focus of previous review papers. A new review in Physics of Plasmas summarizes recent efforts to fabricate targets out of low-density porous materials and highlights the role of target chemistry in laser plasma experiments.

The article first covers design criteria and material selection for low-density targets. For instance, the material must have significant resistance to fracture because the target needs to keep the same shape during the laser irradiation. Also, porous materials containing high atomic number elements are typically required for high-density compression and high-temperature heating of plasma.

The authors then go through a variety of low-density target materials in depth, such as polyacrylate, polysaccharides and different types of aerogels. Methods to process targets of a desired shape, size and geometry are also described. Target shape design is a crucial issue in laser plasma experiments that combines knowledge of polymer chemistry with material engineering.

One method for achieving the required dimensions and shape is mechanical machining using precision diamond tools. Another is in situ molding that polymerizes the material inside a target vessel. A challenge in the field is mass production of low-density materials in order to satisfy demands for high-repetition rate lasers, since current methods tend to be time-consuming.

For the first time, this in-depth review brings together years of research by many groups worldwide so that laboratories can be aware of available materials for their experiments. The authors also hope it will serve as an introductory document to all newcomers to the field.

Source: “A review of low density porous materials used in laser plasma experiments,” by Keiji Nagai, Christopher S. A. Musgrave, and Wigen Nazarov, Physics of Plasmas (2018). The article can be accessed at https://doi.org/10.1063/1.5009689 .