Abstract. A study has been made of photoconductivity in GaP induced by 1.78 and 1.17 eV photons from Q-switched ruby or neodymium lasers. Many-quantum processes were observed with 2 to 7 photons participating simultaneously. Double-photon absorption with a phonon participating has also been investigated. The observed many-quantum transitions confirm the recent ideas about GaP zone structure. Based on a generating function method, the theory of many-quantum transitions is developed which takes into account the peculiarities of crystal zone structure. The experimental data are in satisfactory agreement with the theory. Both the many-quantum theory and the experimental method reported in the present paper permit one to study the zone structure of various crystals and to obtain new or supplementary information on fundamental optical constants of solids.
