The spatially nonlocal response functions are proposed which nearly coincide with the commonly used local response for electromagnetic fields and fluctuations on the mass shell, but differ significantly for the off-shell fluctuating field. It is shown that the fundamental Lifshitz theory using the suggested response functions comes to an agreement with the measurement data for the Casimir force without neglecting the dissipation of free electrons. We demonstrate that reflectances of the on-shell electromagnetic waves calculated using the nonlocal and commonly employed local responses differ only slightly. The Kramers–Kronig relations for nonlocal response functions possessing the first- and second-order poles at zero frequency are derived, i.e., the proposed response satisfies the principle of causality. An application of these results to resolution of the Casimir puzzle, which lies in the fact that the Lifshitz theory is experimentally consistent only with discarded dissipation, is discussed.

提出了空间非局部响应函数，该函数与电磁场和质量壳上波动的常用局部响应几乎一致，但对于壳外波动场则有很大不同。结果表明，使用建议的响应函数的基本李夫希兹理论与卡西米尔力的测量数据一致，而没有忽略自由电子的耗散。我们证明，使用非局部响应和常用局部响应计算的机壳电磁波反射率仅略有不同。推导了具有零频率的一阶和二阶极点的非局部响应函数的Kramers-Kronig关系，即，所提出的响应满足因果关系原理。