Intensity distribution of a capillary-discharge 46.9 nm soft X-ray laser

We realize a Ne-like Ar 46.9 nm soft X-ray laser pumped by a capillary discharge. The study of the laserpulse-intensity distribution is important for applications of soft X-ray lasers. The intensity distribution demonstrates the gain distribution, plasma radius, and axial plasma density that contribute to the study of the laser-pulse formation. To measure the intensity in different positions of the X-ray laser spot, we moved transversally an X-ray diode (XRD) assembled with a slit. We obtain the onedimensional intensity distribution. We find a laser divergence (FWHM) of 4.0 mrad. According to the gain-guided model, we calculate the intensity distribution. The measured divergence of 4.0 mrad roughly corresponds to a plasma radius a approximately equal to 230-250 μm and on-axis electron density n_e ≈ 8.0{bullet operator}10¹⁸ -9.0{bullet operator}10¹⁸ cm^-3. The results of calculations indicate that the divergence of the intensity distribution increases when the plasma radius decreases and the on-axis electron density increases.