Simple hydrodynamic model accounting for intermediate stages of temporal development of laser-induced plasmas

A theoretical model is presented that satisfactorily describes intermediate stages of the propagation of laser-induced plasmas created by focusing laser light on air and other materials. Two stages can be distinguished during the intermediate phase of the plasma expansion. The first is an approximately linear stage, of high speed, governed by the group speed of
X
-ray photons absorbed in the plasma's vicinity. The second is a hydrodynamic expansion with an
X-t
dependence of the form
X \alpha At^{1/3}
used to account for the slower motion of the plasma front behind the blast wave (
R \alpha Bt^{2/5}
). Our theoretical model is compared with results of a particular experiment that best fits the conditions of the theory.