Al-Si-N thin films were deposited using simultaneous laser ablation of silicon and aluminum targets in a nitrogen atmosphere at a substrate temperature of 200 degrees C. The silicon content of the films was studied as a function of the plasma parameters (mean ion kinetic energy and plasma density), produced by the ablation of the silicon target. The plasma parameters were measured by means of a planar Langmuir probe and optical emission spectroscopy. The chemical composition of the films was determined by X-ray photoelectron spectroscopy. The results showed a dependence between the silicon content and the silicon plasma density. Optical emission spectroscopy measurements showed that variations of the working pressure produced changes in the intensity of excited species (N-2(+), Si2+, Al+ and Al-0), and in the incorporation of these elements into the films. For a working pressure of 0.6 Pa, hardness measurements gave a maximum of 30 +/- 1.5 GPa for a silicon content of 4 at.%. The optical constants (refractive index and extinction coefficient) and direct band gap were evaluated as a function of the silicon content in the films.