An integrated fiber-optic Raman sensor has been designed for real-time, nonintrusive detection of liquid nitrogen in liquid oxygen (LOX) at high pressures and high flow rates in order to monitor the quality of LOX used during rocket engine ground testing. The integrated sensor employs a high-power (3-W) Melles Griot diode-pumped, solid-state (DPSS), frequency-doubled Nd:YAG 532-nm laser; a modified Raman probe that has built-in Raman signal filter optics; two high-resolution spectrometers; and photomultiplier tubes (PMTs) with selected bandpass filters to collect both N2 and O2 Raman signals.

The PMT detection units are interfaced with National Instruments’ LabVIEW for fast data acquisition. Studies of sensor performance with different detection systems (i.e., spectrometer and PMT) were carried out. The concentration ratio of N2 and O2 can be inferred by comparing the intensities of the N2 and O2 Raman signals. The final system was fabricated to measure N2 and O22 and LOX.

This work was done by Jagdish P. Singh and Fang-Yu Yueh of Mississippi State University, and Rajamohan R.Kalluru and Louie Harrison of Mississippi Ethanol LLC for Stennis Space Center. For more information contact Jagdish Singh at (662) 325-7375. SSC-00322