Here we report on the first lasing of the Shanghai Soft X-ray FEL user facility (SXFEL). We have achieved the saturation of SASE at 2 nm based on FEL-I and saturation of harmonic lasing self-seeding at 3 nm based on FEL-II. We have also achieved the first lasing of EEHG with a wavelength as short as 5.3 nm.

For a free-electron laser facility, the longitudinal phase space of the beam is essential to the FEL lasing performance. However, the commonly-used diagnostics device such as the transverse deflecting cavity provides a destructive way to measure the beam longitudinal properties, which is not available during beam delivery. Thus, the convolutional neural network is introduced to construct a virtual diagnostic tool that facilitates bunch-to-bunch nondestructive measurement of the longitudinal phase space distribution.