In the present article the interaction between carriers in semi-conductors and a laser beam has been discussed. The influence of intensive light on the intraband motion of an electron was treated, with the conclusion reached that the states of the electron withinone band can still be characterized by a set of quantum numbers-the quasi-momentump and that the wave function contains a factor describing the forced motion in the extremely strong electromagnetic field. The interband transition and other intraband scattering processes were then treated as perturbations. During the transition process, the forced motion changes with the absorption or emission of a number of photons.Following the above discussions, the absorption constants for multi-photon processes of free carrier absorption (with the partipation of the electron-phonon coupling) and the direct transition from valent band to conduction band were calculated. It was estimated that in some materials the two-photon process of the type discussed can be observed easily, especially the direct absorption of two photons in Ge. It was pointed out that using the laser light (the frequency of which is nearly equal to the forbidden energy gap), the absorption lines of the exciton may be shifted to the infrared region, so that the resolving power may be improved. As an example, the case of CdSe was discussed.
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