强外加电场与大调制度下光折变动力学光栅形成研究

Photorefractive Grating Dynamics under Large Modulation and Strong Applied Electric Field

强外加电场与大调制度在光折变效应的研究中已经得到了广泛应用。采用PDECOL算法,严格求解光折变带输运方程,得到外加电场时不同调制度下光折变晶体中随时间变化的空间电荷场、载流子浓度,并讨论了外加电场对它们的影响。通过将物质方程与耦合波方程联立数值求解,可得到光折变光栅形成过程中两波耦合增益系数以及光束条纹相位的变化。模拟结果表明,在强外加电场作用下,两束记录光之间的光强与相位耦合都得到了增强,而原有的解析式忽视了强外加电场与大调制度对空间电荷场相位耦合的影响,此时不再适用。同时发现折射率光栅与记录光束条纹均发生弯曲,并不再保持平行。

Strong applied electric field and large modulation have been widely applied in photorefractive effect research. Photorefractive band transport equations are rigorously solved based on the algorithm of general collocation software for partial differential equations （PDECOL）. Temporal evolutions of space-charge field and charge carrier density in photorefractive crystal have been achieved under different light modulations, and effects of an applied electric field have also been considered. Material equations and coupled wave equations are jointly solved to get the coupling coefficient and phase shift of light pattern during the dynamic procedure of photorefractive grating formation. It is found that, under strong modulation, the intensity coupling and phase coupling between two recording beams are both markedly enhanced, while the analytic equations, which neglect the effects of strong applied electric field and large light modulation on the coupling of the phase of the space charge filed, are not valid any more. Numerical results also show that both the light pattern and index grating are bent and do not keep parallel.