A study on Ar+ laser-assisted chemical beam epitaxy of InP with trimethylindium and tertiarybutylphophine is reported here. In situ monitoring of the laser-assisted growth surface is carried out using reflection high-energy electron diffraction. The growth rates over laser-irradiated and nonirradiated areas are interpreted in terms of physical chemistry of the physisorbed and chemisorbed layers. Two postulations on the photolytic mechanism responsible for growth enhancement with laser are made, which describe the roles of physisorbed group V and group III species in the mechanism.