中文摘要：

在理论上研究了RY型四能级原子系统中的交叉Kerr非线性效应。采用微扰理论和密度矩阵方法导出三阶极化率实部随外加的相干耦合场强度和原子两基态间的无辐射衰减系数之间的关系。结果表明，在双光子Raman共振处，通过减小原子两基态间的无辐射衰减系数和提高外加的相干耦合场的强度，可以获得无吸收增强的交叉Kerr非线性效应。该研究结果在全光学开关上有着重要的应用潜力。

英文摘要：

The cross Kerr nonlinearity effect in RY-type four-level atomic system is theoretically studied Using density-matrix equations and perturbative iterative method, dependence of real part of third-order susceptibility on variations of additional coherent coupling field intensity and nonradiative decay rate between two ground states of atoms are derived. It is found that, by decreasing the nonradiative decay rate between the two ground states and increasing the coupling field intensity, the enhanced cross Kerr nonlinearity with vanishing absorption can be obtained at two-photon Raman resonance. The result is useful in application of all-optical switch