The first observation of two-photon absorption in hard X-ray region




Kenji Tamasaku, Makina Yabashi, Eiji Shigemasa, Kazuto Yamauchi, Hidekazu Mimura, Haruhiko Ohashi



Dr. Kenji Tamasaku and Group Director Makina Yabashi at RIKEN, Associate Professor Eiji Shigemasa at UVSOR, Professor Kazuto Yamauchi at Osaka University, Associate Professor Hidekazu Mimura at Department of Precision Engineering Graduate School of Engineering, The University of Tokyo and Dr. Haruhiko Ohashi at JASRI and their colleagues successfully observed two-photon absorption of X-ray by germanium at the SPring-8 Angstrom Compact Free Electron Laser (SACLA). 
This group developed an XFEL focusing system with a focal size of 100nm. By illuminating intense XFEL beam to germanium, the two-photon absorption phenomena was firstly realized for the first time in the world. Then, they clarified that the sample illuminated by intense X-ray is transformed drastically in femtosedond duration. Finally, they successfully determined the information of the nature of a sample before destruction by combining computer simulations and measured data.  The result is not only an important step in advancement of X-ray nonlinear optics but also meaningful in various XFEL applications such as crystal structure analysis and microscopy.