Diode-laser sensors based on absorption spectroscopy techniques have been developed for characterizing both reactants and products in aeropropulsion flows. We have demonstrated the sensors in pulse detonation engines (PDEs) operating on liquid-JP-10 and gaseous-C2H4 fuels in air and oxygen. The measured properties include unburned and burned gas species concentrations, unburned and burned gas temperature, and burned gas velocity. The information provided by the sensors has been used to verify computational detonation models, thus advancing pulse detonation engine development. Because they provide critical flow properties that have been generally unavailable to aeropropulsion researchers, the sensors are expected to enable novel combustion control schemes. © 2001 by the authors. Published by the American Institute of Aeronautics and Astronautics.