FIBER-OPTIC RAMAN SAMPLING

Figure 12.3. General schematic of fiber-optic Raman sampling, showing the laser-fiber interface and the fiber-spectrometer interface. The bandpass (BP) and band reject (BR) filters are sometimes integrated into the probe head. The fiber-optic (FO) length can vary over a wide range, from less than 1 m to greater than 100 m, depending on the application.

FIBER-OPTIC RAMAN SAMPLING 12.3.1. Laser-Excitation Fiber Interface... 

FIBER-OPTIC RAMAN SAMPLING acetaminophen tablet... 

The chapter thus far has addressed fiber-optic sampling techniques and hardware, illustrated with a few applications. As noted earlier, there has been a wide range of fiber-optic Raman applications presented in the literature, and new reports continue to appear at an accelerating rate. Table 12.4 lists some examples of applications to illustrate the wide variety and breadth of fiberoptic samples. The list is by no means comprehensive, but it should provide the reader with a starting point to explore applications in particular areas. 

Among the advanced techniques employed to follow the cure reaction, Fiber Optic Raman Spectroscopy has been an effective tool. By this technique, both the temperature build-up and the cure advancement of AroCy L-10 could simultaneously be followed. The local temperature of the sample, determined by Ra-man-Stokes and anti-Stokes scattering of a reference peak correlated well with the temperature measured using a thermocouple probe. The extent of cure could be monitored using either individual peaks associated with the reactant or product or by using the entire spectrum [104]. 

Figure 7 Nonfocusing fiber optic Raman probe. The sample is placed in the region where the excitation and collection paths overlap (A) illustrates the overlap for a nonfocusing probe having a single excitation fiber and a single collection fiber (B) illustrates a comrmn configuration using a single excitation fiber and multiple collection fibers.

Figure 7 illustrates a nonfocusing fiber optic Raman probe. Diverging laser light from the delivery fiber illuminates the sample. Adjacent optical fibers collect light scattered back from the sample and deliver the light to the spectrometer. The collection... 

Figure 8 illustrates a focusing fiber optic Raman probe. Light from the laser delivery fiber is sent through a miniature monochromator inside the probehead before being focused onto the sample. Light from the sample is filtered to remove laser light and then injected into the collection fiber for return... 

Because the Raman effect can be successfully integrated with fiber optics, remote sampling is possible. IR spectroscopy can also be interfaced with fiber optics, but the loss of light in the IR region is much higher than the loss in the visible region, and the maximum distance between the sample and the instrument is much smaller for IR spectroscopy than for Raman spectroscopy. 

Fiber-Optic Probes. Fiber-optic probes provide remote sampling capabilities to Raman instmmentation, are stable, and give reproducible signals. Their historical niche has been in environmental monitoring. More recently these probes have been used in chemical process control and related areas such as incoming materials inspection. 

Lewis I.R., Griffiths P.R., Raman Spectrometry with Fiber-Optic Sampling, Appl. Spectrosc., 1996 50 (10) 12A - 30A. 

---