Haoyan Jia, Senlin Huang, Yi Jiao, Jingyi Li, Kexin Liu, Shuai Liu, Weihang Liu, Zhongqi Liu, Tianyun Long, Weilun Qin, Sheng Zhao. Research advances in ultrafast X-ray free-electron lasers[J]. High Power Laser and Particle Beams, 2022, 34(5): 054001