Ultrashort-pulse laser excitation of dielectrics is an intricate problem due to the strong coupling between the rapidly changing material properties and the light. In the present paper, details of a model based on a multiple-rate-equation description of the conduction band are provided. The model is verified by comparison with recent experimental measurements of the transient optical properties in combination with ablation-depth determinations. The excitation process from the first creation of conduction-band electrons at low intensities to the formation of a highly-excited plasma and associated material fragmentation is explained by the model. For quartz samples, the optical properties are strongly influenced by self-trapped excitons, and the associated additions to the model are described.