A complete set of reflection and transmission coefficients of microwave for a stratified unmagnetized laser-induced-plasma
slab by using the scattering matrix method (SMM) is presented. The nonuniform unmagnetized laser-induced-plasma
slab is modeled by a number of subslabs, and each subslab has a fixed electron density. Because the field in each
subslab can be represented by the sum of the reflected and incident components, the partial reflection and transmission
coefficients can be obtained by successively matching boundary conditions at all interfaces. In plasma, the surface
reflecting the microwave is defined by the critical surface, where the plasma angular frequency equals to the microwave
angular frequency. The partial reflection coefficients of microwave at the critical surface as the functions of the
microwave frequency, and collision frequency for a Lorentz electron density profile are investigated.