Raman microprobe fibers

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of 1 /rm, much better than the diffraction limit imposed on ir microscopes (213). Fiber-optic probes can be used in process monitoring (214). 

Optical Fibers. Several manufacturers of optical fibers have suggested that a Raman microprobe could be a useful tool in characterizing fibers. The literature shows that it is possible to monitor the concentration of additives to silica down to the 1 mole percent level, f 13-17) Polished sections of preforms or drawn fibers have been monitored in the microprobe in this laboratory. 

Atalla, R.H. Raman spectroscopy and Raman microprobe Valuable new tools for characterizing wood and wood pulp fibers. J. Wood Chem. Technol. 7, 115-131 (1987)... 

Cuesta A, Dhamelincourt P, Laureyns J, Martinez Alonso A, Tascon JMD, Effect of various treatments on carbon fiber surfaces studied by Raman microprobe spectrometry, 52(3), 356-360, 1998. 

An important development in Raman spectroscopy has been the coupling cf the spectrometer to an optical microscope. This allows the chemical and structural analysis described above to be applied to sample volumes only 1 across [38]. No more sample preparation is required than that for optical microscopy, and the microscope itself can be used to locate and record the area which is analyzed. This has obvious practical application to the characterization of small impurities or dispersed phases in polymer samples. This instrument, which may be called the micro-Raman spectrometer, the Raman microprobe or the Molecular Optics Laser Examiner [39] has also been applied to the study of mechanical properties in polymer fibers and composites. It can act as a non-invasive strain gauge with 1 fim resolution, and this type of work has recently been reviewed by Meier and Kip [40]. Even if the sample is large and homogeneous, there may be advantages in using the micro-Raman instrument. The microscope... 

Figure 14.36 a) Raman microprobe spectra (with 780 nm exdtation) of two different red-dyed polyester fibers. Polyester bands are marked with an asterisk. b) Raman microprobe spectra (with 780 nm excitation) of a blue-dyed fiber. 

A) Fiber with dye (B) Fiber only, after solvent extraction of dye (C) Dye spectrum obtained by computer subtraction of B from A. Reproduced with permission from Keen, I. R, etal. "Characterization of Fibers by Raman Microprobe Spectroscopy. " Journal of Forensic Sciences 43 (7998j, 82- 9. Copyright 1998, ASTM International. 

Keen, L P., et al. "Characterization of Fibers by Raman Microprobe Spectroscopy." Journal of Forensic Sciences 43 (1998), 82-89. 

N Everall, K Davis, H Owen, MJ Pelletier, J Slater. Density mapping in poly(ethylene terephthal-ate) using a fiber-coupled Raman microprobe and partial least-squares calibration. Appl Spectrosc 50 388-393, 1996. 

IR Lewis, JM Shaver, ML Samford. Advances in fiber-coupled Raman microprobes and chemical mapping. In DB Williams, R Shimizu, eds. Institute of Physics Conference Series No. 165. Philadelphia Institute of Physics, 2000, pp 91-92. 

J Barbillat, P Dhamelincourt, M Delhaye, E Da Silva. Raman confocal microprobing, imaging and fibre-optic remote sensing A further step in molecular analysis. J Raman Spectrosc 25 3-11, 1994. NQ Dao, M Jouan. The Raman laser fiber optics (RLFO) method and its applications. Sensors Actuators B Chem 11 147-160, 1993. 

LE Jurdana, KP Ghiggino, KW Nugent, IH Leaver. Confocal laser Raman microprobe studies of keratin fibers. Textile Res J 65 593-600, 1995. 

Skoog et al. [2] emphasized the instmmentation advances of the 1980s and early 1990s. Both Fourier-transform Raman (FT-Raman) spectrometers and single-stage spectrographs are discussed. There is some discussion of optical fiber probes, but none of the Raman microprobe. The authors sketch the theory of Raman scattering and present a classical (polarizability derivative) treatment of selection rules and intensity. Resonance enhancement and surface enhancement are treated briefly. In a textbook noted for its emphasis on instrumentation, there is little discussion of current applications. 

Figure 14.2 The compositional change at tendon-to-bone insertion site and the corresponding change of mechanical properties, (a) Relative mineral content evaluated from confocal Raman microprobe spectroscopy measurements, showing the ratio of the areas of the 960 Acm" PO4 peak to the 2940Acm collagen peak, across the tendon-to-bone insertion, (b) Bounds and estimates for the axial elastic modulus ( ) of a partially mineralized fiber. Mineral stiffens fibers dramatically at volume fraction above the percolation threshold = 0.5), indicated by the arrows. Percolation occurs at lower volume fraction for regions of enhanced mineralization elongated parallel to the fiber axis.

In Chapter 2, the historical impact of these devices have been reviewed. These individual components have been assembled to produce three popular and fundamental types of Raman spectrometers the laboratory Fourier transform (FT)-Raman system [1,2], the CCD-based microprobe [3], and the fiber-coupled CCD-based process Raman analyzer... 

Figure 31 Schematic illustration of RSNOM instrument constructed by the authors. E = exciting light, FP = fiber probe, DP = dithering piezo, DD = dither detection, LD = laser diode, PD = photodiode, SS = piezo XYZ scanning stage, TCO = transmission collection objective, RCO = reflection collection objective, M = mirror, RIMM = Raman imaging microprobe/microscope. The various movable mirrors allow the instrument to be operated in reflection or transmission modes and allow the operator to observe the probe-sample region through the collection optics this aids the coarse approach of the tip to the sample and helps optical alignment of the system.

Figure 25 Schematic representation of a remote Raman macroprobe or microprobe using optical fibers.

The final example cited in this subsection, the use of Raman spectroscopy to the study of pharmaceuticals, is in the area of identification and quantitation of materials in finished pharmaceutical products and formulations. A host of authors, using everything from bench-top laboratory analyzers, microprobes, and fiber-optics sampling devices have demonstrated the use of Raman spectroscopy for identification and quantification [117-122]. Limits of detection and reproducibility for many of the materials studied were reported. 

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