Optimization of a laser plasma-based x-ray source according to WDM absorption spectroscopy requirements

X-ray absorption spectroscopy is a well-accepted diagnostic for warm dense matter experimental studies. It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in a spectral range of interest. In the present work, we discuss choosing its optimum material and thickness to get a bright source in the wavelength range of 2-6 A (~2-6 keV) considering relatively low-Z elements. We demonstrate that the highest emissivity of solid aluminium and silicon foil targets irradiated with a 1 ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10 μm. An outer plastic layer can increase the emissivity even further.