Laser-induced breakdown spectroscopy (LIBS), based on studying the spectrum emitted in a laser ablation process, is a potential method for in situ studies of the compositions of mixed layers deposited on the first walls of future fusion reactors [1]. By LIBS, these layers could be monitored in between plasma discharges without the need for removing any wall components. In this contribution, the aim is to find optimal experimental parameters for studying ITERrelevant materials, especially D-containing mixed layers of Be and W. This is done by varying the fluence of the laser beam, triggering of the measurements, and the laser wavelength.