Laser ablation from one- and two-component targets into a diluted gas background is simulated by combined direct simulation-test particle Monte Carlo method. The spatial and velocity distributions of particles deposited at the plane substrate are calculated. The approach developed has allowed us to consider the influence of the collisions both among the ablated particles and between the ablated and ambient gas particles on the uniformity of film stoichiometry. It is found that the increase of the background gas pressure results in the more uniform distribution of the stoichiometrical ratio of the deposited particles with different masses.