Fiber optic Raman sensor to monitor the concentration ratio of nitrogen and oxygen in a cryogenic mixture

A spontaneous Raman scattering optical fiber sensor was developed for a specific need of the National Aeronautics and Space Administration (NASA) for long-term detection and monitoring of the purity of liquid oxygen (L[O.sub.2]) in the oxidizer feed line during ground testing of rocket engines. The Raman peak intensity ratios for liquid nitrogen (L[N.sup.2]) and L[O.sub.2] with varied weight ratios (L[N.sup.2]/L[O.sub.2]) were analyzed for their applicability to impurity sensing. The study of the sensor performance with different excitation light sources has helped to design a miniaturized, cost-effective system for this application. The optimal system response time of this miniaturized sensor for L[N.sup.2]/L[O.sub.2] measurement was found to be in the range of a few seconds. It will need to be further reduced to the millisecond range for real-time, quantitative monitoring of the quality of cryogenic fluids in a harsh envioronment. OCIS codes: 0300.6450, 300.6330, 300.0300, 140.3550, 170.5660, 060.2370.