Theoretical and experimental study on X-ray parametric nonlinear processes for application to material science

我们从理论和实验上研究了X射线到光学区的参数下转换(PDC)，这是X射线区的一种非线性光学过程。我们发现x射线PDC是光学Fano效应，是从Fano谱推断二阶非线性极化率的理论。我们还证明了二阶非线性极化率包括光学频率的线性极化率，并成功地可视化了203A的局域光学响应，分辨率高达0.54A。

We investigate both theoretically and experimentally parametric down-conversion(PDC) of x-rays into optical region, which is one of nonlinear optical processes in the x-ray region. We find that x-ray PDC is observed as the optical Fano effect and a theory to deduce the second order nonlinear susceptibility from the Fano spectra. We also show that the second order nonlinear susceptibility includes the linear susceptibility at the optical frequency, and succeed in visualizing the local optical response at 203 A with a resolution as fine as 0.54 A.