Rugged Fiber-Optic Raman Probe for Process Monitoring Applications

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Abstract
We report on the development of a simple, rugged fiber-optic probe for process Raman measurements, in which laser line rejection is based on an absorptive longpass filter made from a direct bandgap CdTe semiconductor. The probe can be used with a fixed wavelength laser at 830 nm, and Raman spectra can be recorded down to 200 cm−1 from the laser line. The filter thickness can be adjusted for final turning of the filter edge, as the edge slope is almost independent of thickness in the range 0.1 to 1 mm. Other properties of the probe, such as its signal-to-noise ratio and signal-to-background ratio, are shown to compare well with those of a state-of-the-art probe based on holographic notch filter techniques.