Overview of the observed spectra (black points), fitted curves (blue), and de-convolved transmission curves with FEL emission centred near the (2,0)2 wavelength (upper) and the (2,0)3 wavelength (lower)

Figure 2. Overview of the observed spectra (black points), fitted curves (blue), and de-convolved transmission curves with FEL emission centred near the (2,0)2 wavelength (upper) and the (2,0)3 wavelength (lower). Labels are column density / (1017 cm−2).

Abstract

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.