  Here we show that, despite a massive incident flux of energetic species,
plasmas can induce transient cooling of a material surface. Using time-resolved
optical thermometry in-situ with this plasma excitation, we reveal the novel
underlying physics that drive this `plasma cooling' that is driven by the
diverse chemical and energetic species that comprise this fourth state of
matter. We show that the photons and massive particles in the plasma impart
energy to different chemical species on a surface, leading to local and
temporally changing temperatures that lead to both increases and decreases in
temperature on the surface of the sample, even though energy is being imparted
to the material. This balance comes from the interplay between chemical
reactions, momentum transfer, and energy exchange which occur on different time
scales over the course of picoseconds to milliseconds. Thus, we show that
through energetically exciting a material with a plasma, we can induce cooling,
which can lead to revolutionary advances in refrigeration and thermal
mitigation with this new process that is not inhibited by the same limitations
in the current state-of-the-art systems.
