DETERMINATION OF MONOMETHYLHYDRAZINE WITH A HIGH-THROUGHPUT, ALL-FIBER NEAR-INFRARED SPECTROMETER BASED ON AN INTEGRATED ACOUSTOOPTIC TUNABLE FILTER AND AN ERBIUM-DOPED FIBER AMPLIFIER

A novel integrated acoustooptic tunable filter (IAOTF) has been develo ped, This tunable filter is based on the Bragg interactions between wa veguide and surface acoustic waves, Compared to (bulk) AOTF, its advan tages include all-fiber construction, smaller size, narrower spectral resolution (1.7 nm), higher diffraction efficiency (37%), and lower rf power requirement (150 mW). A relatively narrow spectral tuning range (about 80 nm) is the only drawback for this integrated tunable filter . However, this disadvantage was overcome by judiciously using the fil ter for measurements in which its tuning range is coincident with the light source and also with absorption bands of analytes. In fact, an a ll-fiber, compact, high-throughput near-infrared spectrophotometer has been successfully constructed by synergistic use of this integrated A OTF and the erbium-doped fiber amplifier (EDFA), which has been shown to provide high intensity and wide spectral bandwidth in the near-infr ared region from 1500 to 1600 nm. This spectral region is particularly useful for the determination of samples which have O-H and/or N-H gro ups, The all-fiber nature, compactness, high throughput, and high sens itivity of this spectrophotometer make it particularly suitable for on -line and real-time detection of trace gases in hostile environments, including leak detection of monomethylhydrazine (at a limit of detecti on of 191 ppm), which is often used as the hypergolic propellant for t he space shuttle thruster systems.