Excitation pulse energy dependence of gain volume in amplifying and scattering medium

The excitation pulse, energy dependence of the gain volume in an amplifying and scattering medium was examined using a two-beam spatial-correlation method. The volume increased with 1/3 power of the excitation pulse energy in the weak excitation region, and then approached a critical value when the excitation energy was further increased. Numerical simulations explain the experimental results well, and a phenomenological model dealing with the total excitation in the gain volume via a rate equation is also discussed in order to explain the dependence.