The statistical average of the Langevin noise that describes the spontaneous radiation noise coupling into a given mode is determined by the Biorthogonality of the transverses modes ( K factor) and their eigenvalues. 说明描述耦合到任意给定模式自发辐射噪声(朗之万噪声)项的统计平均可以用横模的双正交性(即过量噪声K因子)与特征值特性来描述。