IR fibers

Gregory, C. C., IR Fibers Shed Poor Reputation at Longer... 

Hewak D.W., Taylor E., Payne D.N., Optical amplifiers and lasers in IR fibers, Proc.SPIE 3849 (1999), Boston. 

Ignition Quality Tester (IQT), 12 422-423 Ignition resistant (IR) fiber blends, 13 385 Ignition-resistant applications, VDC copolymers in, 25 737 Ignition-resistant materials, 11 449-450 Ignition suppression, by silver, 22 640 Ignition temperatures, 10 871 21 840 of ethers, 10 579... 

Gobel R, Krska R, Neal S, et al. 1994. Performance studies of an ir fiber optic sensor for chlorinated hydrocarbons in water. Fresenius Journal of Analytical Chemistry 350(7-9) 514-519. 

While UV-vis fibers are much less prone to fiber breakage than mid-IR fibers, excessive mechanical stress may still break the fibers. The miifimum bending radius as specified by the supplier should be observed, and excessive mechanical stress should be avoided. 

N.K. Mehta, J. Goenaga-Polo, S.P Hemandez-Rivera, D. Hernandez, M.A. Thomson and P.J. MeUing, Development of an in situ spectroscopic method for cleaning validation using mid-IR fiber optics. Spectroscopy, 18(4), 14 (2003). 

J. Lin and C.W. Brown, Near-IR fiber-optic temperature sensor, Appl. Spectrosc., 47, 62-68 (1993). 

The use of fiber optics and fiber-optic multiplexing can increase the number of analysis points, and hence can reduce the overall costs related to a single analyzer. This approach has been used successfully with NIR instrumentation, where typically up to 8 points can be handled. As noted earlier, the use of fiber-optics with mid-IR Fourier transform instruments has been limited. Although in the past commercial multiplexers have been available for mid-IR fiber systems, their use has been minimal. 

As shown in Table 1, hollow waveguides (HWGs) are the only fibers capable of transmitting radiation across the entire MIR band at comparatively low attenuation losses similar to usually more narrow-band solid-core IR fibers. 

One of the most important sensors needed is one that reliably monitors cell density. An IR fiber-optic cell density probe has been used for this because it can directly monitor cell growth (without dilution) in high-cell-density bacterial fermentations. The ability to do an online sample filtration through the use of hollow fibers or rotating filters has made possible continuous, online measurement of glucose, lactate, and other metabolites. However, glucose, nitrogen substrate, and phosphate sensors that can withstand repeated system sterilization are still needed. 

There are at this time no IR-fibers which fulfill all of these demands. The mainly used fibers are made of poly-crystalline silver halide (refractive index 2.2 at 10.6 pm) with very good transmission over the whole MIR (2 to 16 pm, see Fig.6.5-5), and good mechanical properties. The disadvantages are that they react with many commonly used metals and that they are sensitive to visible radiation, especially to UV radiation (Ceram optec, 1991). 

Figure 6.5-5 Transmission for some IR-fibers (Im in length). (A) Zirconium fluoride (Fiber System, 1991), (B) chalcogenide (Fiber Systems, 1991), (C) silver halide (Ceram Optec, 1991).

There are still two ways of using IR-fibers. First, a little part of the fiber is cut and used as an cylindrical IRE. The second way is to cover a little part of a long fiber where the other parts have the function to transport the light from the source to the sensitive part and to forward it to the detector or spectrometer. Since these fibers have a thickness of several hundred pm up to 1 mm, the number of reflections may be greater, making the detection limit smaller than in the described ATR experiments. 

Besides the poor chemieal or mechanical properties of presently available IR fibers have some additionally inherent disadvantages which limit their usage considerably. From Eq. 6.5-1 and 6.5-2 it can be seen that the effective thickness, the number of reflections... 

R. A. Lodder and L. Cassis, Arterial Analysis with a Novel Near-IR Fiber-Optic Probe, Spectroscopy, 5(7), 12 (1990). 

Krska R, Taga K, Kellner R. 1993. New IR fiber-optic chemical sensor for in situ measurements of chlorinated hydrocarbons in water. Applied Spectroscopy 47(9) 1484-1487. 

Mid-IR fiber optics provides a convenient way to monitor many kinds of chemical reactions in situ and in real time. Isocyanate chemistry, both in the solution phase and in the form of urethane foams and binders, lends itself well to this approach. It is shown in this paper that the calibration of mid-IR fiber optics is simple and transferable between probes and probe heads, and that useful information about reaction rates and extent of cure can be obtained by simple peak area measurements in many cases. 

The monitoring of isocyanate reactions, including urethane formation in foams and binders, can be conveniently carried out using mid-IR fiber optic spectroscopy. Once the spectroscopic evolution of a particular reaction is understood, a simple measure of the degree of curing of a urethane material can be developed by using a ratio of peak areas for a characteristic peak arising from the precursor and one from the product. In case such as that of the simulated solid fuel discussed above, the small batch reactions used in the industry can be monitored in situ when this method is combined with the use of mid-IR fiber optics, which offer a combination of convenience and robust calibration. 

Table 1. Categories of the most important of IR fibers data reproduced from Harrington, 2010.

FT-IR Fiber Optics for Remote Sampling in Mid-Infrared, Nicolet Specifications, Nicolet Instrument, Madison, 1999. 

AsSeTe (amorphous) 2.500 11.11 4000 900 1159 261 2.80 Good for Mid-IR fiber optics chemically inert. 

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