Journal Article free-electron laser Fourier-transform limited pulse Review X-ray beamline design photodetectors time-delay-compensated monochromator ultrashort pulse propagation 2D polarized materials COVID-19 Classification CuBr Data imbalance Deep supervised learning Research Support, Non-U.S. Gov't Self-adaptive auxiliary loss beamline design capacitance matching chemical vapor deposition diffraction gratings dynamic key ferroelectric materials ferromagnetic materials ferrovalley materials finite-element modelling grating monochromator hysteresis infrared inorganic materials magnetic propulsion