Materials are prepared fo
Materials are prepared for use in this medium by "baking them out" to remove volatiles. The technique of sputtering is used to deposit coatings and films in the presence of this medium. A medium that is similar to this one is said to be "rarefied". This medium has zero electromagnetic susceptibility, and hence a refractive index of precisely 1, not accounting for its polarization by virtual pair production. The beam lines of particle accelerators are filled with this medium, as are cathode ray tubes. This medium is ideally characterized by having zero pressure. For 10 points, name this medium that is characterized by the absence of matter, found in outer space.
Materials are prepared for use in this medium by "baking them out" to remove volatiles.
 vacuum [or free space; accept partial vacuum] 