الفهرس 
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Abstract
The processes of multiphoton transitions In semi-conductors are theoretically investigated. The three-photon inter electronic transitions in crystals are studied. A simple procedure is jive to sb* do polarization dependence in three-photon spectroscopy. The absorption rate is separated Into dynamically and geometrical parts. The first supplies the relative strength of the interband electronic tranaluona to all the allowed final states with different symmetries, and the second depends on the polarization dependence of the, sboorption rate. The four-photon transitions rate in investipted. An for four-photon absorption coefficient is calculated using fourth order perturbation theory, through different band model. The five band model shown to be dominant.