Enhancement of two-wave mixing gain coefficient by resonant mechanism in photorefractive semiconductor

Abstract

In this paper, two-wave mixing in photorefractive semiconductors at large modulation depth is theoretically analyzed and discussed. An analytic expression of space-charge field normalized to the weak externally applied dc electric field value is presented and a one center-two band model which includes both temperature and electron-hole is considered. The variations of space-charge field with dc field and Fe2+ concentration are investigated. Furthermore, the variations of the gain coefficient with temperature, intensity beam ratio, incident angle, and incident light intensity are analyzed. The results show that both the space-charge field and gain coefficient can increase with a stronger dc field. When the dc field is less than 10 kV/cm, applying a strong dc field can significantly improve the space charge filed and gain coefficient. As the incident intensity rises, under the influence of the intensity-dependent resonant effect, a maximum gain coefficient is achieved for an optimum incident intensity which increases with the temperature. Besides, an optimal angle of incidence is obtained at which the gain coefficient is maximum. It is demonstrated that the optimal incident intensity of 21 mW/cm2 and the optimal angle of 5° can be obtained under the temperature of 300 K and the dc field of 10 kV/cm conditions. The present work can provide theoretical guidance for the practical application of two-wave mixing in photorefractive crystals.