Single-shot simulation at a column density of 68 <b>×</b> 10<sup>17</sup> cm<sup>−2</sup> near the <em>n</em> = 3 and <em>n</em> = 4 resonances

<p><strong>Figure 5.</strong> Single-shot simulation at a column density of 68 <b>×</b> 10<sup>17</sup> cm<sup>−2</sup> near the <em>n</em> = 3 and <em>n</em> = 4 resonances. The upper panel shows the simulated SASE wavelength profile (red), the transmission of the gas cell (black, same <em>x</em>-axis), the phase due to absorption (black, right-hand <em>y</em>-axis), and the transmitted wavelength profile (blue). The lower panel shows the time profile of the electric field before (red) and after (blue) the gas cell.</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p>