Surface processes during the heteroepitaxy of GaP on Si under pulsed chemical beam epitaxy conditions were investigated simultaneously by the optical methods reflectance difference/anisotropy spectroscopy, p-polarized reflectance spectroscopy (PRS), and laser light scattering. Our studies were performed during both cyclic and interrupted growth, where the surface was exposed to individual pulses of the precursors triethylgallium (TEG) and tertiarybutylphosphine (TBP). The data show that the three optical probes provide different perspectives of growth. Several surface processes exhibit time constants of the order of 1 s. One such process is the clustering of Ga atoms, or less likely, of TEG fragments, that occurs with TEG exposure. The optical data also show that TBP dealkylation occurs essentially instantaneously upon arrival at the surface, and that TEG dealkylation is the rate-limiting step. The PRS data exhibit fine structure that shows that heteroepitaxial growth can be described by a four-phase model consisting of the substrate, a GaP layer, a surface reaction layer containing all adsorbed species not yet incorporated in the growing layer, and the ambient. By assuming that this surface layer is very thin we derive approximate equations that allow us to treat the PRS response quantitatively.