We propose to design, build and evaluate a prototype of a compact, robust, optically-based sensor for making temperature and multi-species concentration measurements in propulsion system ground and flight test environments. This system will utilize a widely tunable near infrared light source to make absorption measurements of combustion reactant and products in the combustion zone (with accuracy from 100-1000 ppm). Although possible to tune over a very wide wavelength range, during phase-II we propose to develop the light source which will be able to continuously tune from 1.4 to 1.8 microns while maintaining a narrow bandwidth of 0.01 cm-1 using a novel combination of acousto- and electro-optically controlled devices. The rapid tunability of this light source will obviate the need for dense multiplexing of multiple wavelengths as signals can be multiplexed in time while maintaining fast temporal response. Furthermore, the wide spectral bandwidth allows for the selection of the optimum absorption transitions, without regard for the commercial availability of narrow bandwidth diode lasers. The proposed instrumentation will be environmentally rugged, with the ability to withstand extreme ranges of temperature, humidity, vibration and shock conditions. Further, the system will possess auto-calibration capabilities, fast response time (few microseconds) and can be battery operated.