Near-infrared spectroscop optical fibers used

Commercial analyzers mainly intended for laboratory use have been adapted with optical fibers to most spectrophotometers (Photonetics Sodety). Assemblies of fibers on spec-trofluorimeters [82,199] and Raman [167,177,193,200], infrared (IR), near-IR [189] mid-IR [201], and Fourier transform (FT) IR [202,203] spectrometers have already proved their value for remote spectroscopic sensing. However, these units are only partially adequate for continuous in situ process control because of their weak dynamic range after coupling of fibers and a maladjusted numerical aperture with respect to optical fibers. Photodiode-array instruments, without spectral scanning, are nevertheless the best for on-line control. This class includes the series of Hewlett-Packard HP 8450-8452 spectrophotometers and the Fluo 2(X)1 spectrometer (Dilor Society) [175] for fluorimetric and Raman determinations. 

Since the mid-1990s, there has been plenty of activity regarding the use of spectroscopic techniques for on-line evaluation of polymer properties [143-146]. This has been possible due to the recent development of fiber-optic probes, which allow in-situ measurements in remote and harsh environments (high temperatures, pressures, toxic environments, and so on). An additional advantage is that a fiber-optic probe can be installed in an existing reactor within a short time without expensive modifications. Fluorescent, ultraviolet (UV), infrared (IR), near-infrared (NIR), mid-infrared (MIR) and Raman spectroscopic techniques can be used for polymerization reaction monitoring. These can be divided between absorption- and emission-based techniques. IR, NIR, and MIR are absorption-based. 

---