This paper presents a study of the extinction process of a HF cw chemical laser beam when passing through a moving multicomponent and polydisperse medium composed of particles of carbon and magnesium oxide about 1 mm in size at an ambient pressure of 50 Pa . We also describe in the paper an experimental complex developed for studying the processes of light interaction with disperse media of different densities under conditions of low–pressure atmosphere. Numerical values of the volume extinction coefficient are given as a function of particles flow density.