The development of ultra-bright extreme ultraviolet (EUV) and X-ray free electron laser (FEL) sources has enabled the extension of wave-mixing approaches into the short wavelength regime. Such a class of experiments relies upon nonlinear interactions among multiple light pulses offering a unique tool for exploring the dynamics of ultrafast processes and correlations between selected excitations at relevant length and time scales adding elemental and site selectivity as well. Besides the availability of a suitable photon source, the implementation of wave mixing methodology requires efforts in developing the instrumental set-up. We have realized at the FERMI FEL two dedicated set-ups to handle multiple FEL beams with preselected parameters in a non-collinear fashion and control their interaction sequence at the target. These unique apparatuses, combined with the exceptional characteristics of the seeded FERMI FEL, have allowed us to make the first steps into this field and further advances are foreseen in the near future.

超亮极紫外 (EUV) 和 X 射线自由电子激光 (FEL) 源的发展使波混合方法能够扩展到短波长区域。此类实验依赖于多个光脉冲之间的非线性相互作用，为探索超快过程的动力学以及相关长度和时间尺度上选定激发之间的相关性提供了独特的工具，同时增加了元素和位点选择性。除了提供合适的光子源外，波混合方法的实施还需要努力开发仪器装置。我们在 FERMI FEL 实现了两个专用设置，以非共线方式处理具有预选参数的多个 FEL 光束，并控制它们在目标处的交互顺序。这些独特的仪器，