The detailed structure of the active medium in a gas-dynamic laser is analysed. The parameters of regular and stochastic phase field components are reconstructed from the results of processing the schlieren patterns of the flow field simulated by cold air. The second-order characteristics are obtained in the form of the spectral density of power and correlation distribution function of stochastic inhomogeneities; the integral scale of the phase perturbation is also determined. The standard deviations in perturbations of the regular and stochastic components are compared and a correct prediction of laser radiation parameters is made for several cases of the laser beam propagation through the phase-perturbing active medium.