A pulsed slit-jet expansion source capable of generating moderate velocity-collimated pathlengths(∼1 cm)of rovibronically cooled target molecules for spectroscopic interrogation is described and characterized. Based upon the modification of a commercially available current loop-actuated design, this apparatus produces conductance-limited pulses of⩽50 &mgr;sduration at repetition rates of up to 20 pps. The short temporal length of the emerging gas pulse greatly alleviates the demands imposed upon vacuum pumping systems and enables the use of higher stagnation pressures in the expansion process. ©1998 American Institute of Physics.