  The design and characterization of a new laser-desorption molecular beam
source, tailored for use in x-ray-free-electron-laser and
ultrashort-pulse-laser imaging experiments, is presented. It consists of a
single mechanical unit containing all source components, including the
molecular-beam valve, the sample, and the fiber-coupled desorption laser, which
is movable in five axes, as required for experiments at central facilities.
Utilizing strong-field ionization, we characterize the produced molecular beam
and evaluate the influence of desorption laser pulse energy, relative timing of
valve opening and desorption laser, sample bar height, and which part of the
molecular packet is probed on the sample properties. Strong-field ionization
acts as a universal probe and allows to detect all species present in the
molecular beam, and hence enables us to analyze the purity of the produced
molecular beam, including molecular fragments. We present optimized
experimental parameters for the production of the purest molecular beam,
containing the highest yield of intact parent ions, which we find to be very
sensitive to the placement of the desorbed-molecules plume within the
supersonic expansion.
