超快非线性光谱技术(远红外至近紫外波段)是探测物质动力学过程及对称性的有效手段。近年来X射线自由电子激光技术的发展使超快光谱学测量拓展至X射线波段成为可能。文章对相关的研究进展进行了评述，并着重强调X射线波段的超快非线性光谱技术对于加深人们对物理和化学现象以及材料性质等的理解具有重要意义。

Nonlinear and ultrafast optical (far infrared to near ultraviolet) spectroscopic techniques are versatile tools for probing material dynamics and symmetries. Recent advances in the design of X-ray free electron lasers now allow for the extension of ultrafast spectroscopy to the X-ray region. We discuss the examples of such extensions highlighting the unique contributions that implementation of ultrafast and nonlinear spectroscopy in the X-ray region can make to deepen our understandings of chemical and physical phenomena and material properties.