Potential High-Spatial Resolution In-Situ Imaging of Soft X-Ray Laser Pulses With ZnO Crystal

We show that a hydrothermal method-grown ZnO is a potential material of an imaging device for soft X-ray laser diagnostics. The beam profile of a soft X-ray laser was evaluated by characterizing the exciton emission patterns of ZnO. The single shot image of emission patterns is clear enough to monitor the evolution of the beam radius around the focal point. By plotting the emission pattern radii at each position, the beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 μm and 21 μm in the horizontal and vertical axis, respectively. The divergence angle was estimated to be around 7.2 mrad and 11 mrad in the horizontal and vertical axis, respectively. The beam quality evaluated from the M² factor was 47 along the horizontal axis and 50 along the vertical axis. Spatial resolution of the magnifier was estimated to be 6 μm and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as a high-spatial resolution in-situ imaging device that would play a crucial role in the development and application of soft X-ray light sources.