Fiber optical microscopy

Optical properties of fibers are measured by light microscopy methods. ASTM D276 describes the procedure for fiber identification using refractive indexes and birefringence. Other methods for determining fiber optical properties have been discussed (3,38—44). However, different methods of determining optical properties may give different results (42). 

Similar to prepared metallographic samples, the injection molded samples were cut along the flow direction, smoothed, and polished in order to expose their internal surface. After proper etching, the treated surfaces of the flank cross-section were photographed using a polarized light optical microscopy. Based on the color differences between the TLCP and matrix, volume fraction and aspect ratio of the TLCP fibers were measured [23]. 

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

Nagahara, T., Imura, K. and Okamoto, H. (2004) Time-resolved scanning near-field optical microscopy with supercontinuum light pulses generated in microstructure fiber. Rev. Sci. Instrum., 75, 4528-4533. 

Figure 3. Images of a cross-section of carbon fibers after propylene pyrolysis. 3a Scanning Electron Microscopy of a piece of the carbon cloth. 3b optical microscopy (crossed polarizers with a wave retarding plate).

Have good photostability. Photostability is particularly critical if high light intensities are used for interrogation (such as in microscopy or fiber-optic microsensors) or if the measurements are performed over a long time. Photodegradation always affects luminescence intensity but is usually less critical in case of the decay time measurements since this parameter can remain unaffected by photobleaching. 

Fluorescent pH indicators offer much better sensitivity than the classical dyes such as phenolphthalein, thymol blue, etc., based on color change. They are thus widely used in analytical chemistry, bioanalytical chemistry, cellular biology (for measuring intracellular pH), medicine (for monitoring pH and pCC>2 in blood pCC>2 is determined via the bicarbonate couple). Fluorescence microscopy can provide spatial information on pH. Moreover, remote sensing of pH is possible by means of fiber optic chemical sensors. 

Several papers have been published in which, instead of concentrating on specific reactions, the technology was highlighted. One, by Marose et al.,7 discusses the various optics, fiber optics, and the probe designs that allow in situ monitoring. They describe the various optical density probes used for biomass determination in situ microscopy, optical biosensors, and specific sensors such as NIR and fluorescence. 

The fiber fragment length can be measured using a conventional optical microscope for transparent matrix composites, notably those containing thermoset polymer matrices. The photoelastic technique along with polarized optical microscopy allows the spatial distribution of stresses to be evaluated in the matrix around the fiber and near its broken ends. 

The nature of the phase formed in the slow coagulation experiment can be deduced on the basis of its thermal transitions, and from its X-ray diffraction pattern. In the DSC trace of the slowly coagulated PBT-MSA-water system shown in Figure 6, three endothermic transitions are observed between 90 °C and 240 °C. Corresponding transitions were observed by optical microscopy using a hot stage. Solid PBT fibers or films do not exhibit thermal transitions below about 650°C (1). 

Infrared microscopy allows the characterization of minute amounts of a material or trace contaminants or additives. Samples as small as 10 pm can be studied using IR microscopy. The microscope, often using fiber optics, allows IR radiation to be pinpointed. 

Similarly to FTIR spectroscopy, Raman spectroscopy is a versatile technique of analyzing both organic and inorganic materials that has experienced noticeable growth in the field of art and art conservation, in parallel to the improvement of the instrumentation [38]. In particular, the introduction of fiber optic devices has made feasible the development of mobile Raman equipments, enabling nondestructive in situ analyses [39]. On the other hand, the coupling of Raman spectroscopes with optical microscopes has given rise to Raman microscopy vide infra). 

Techniques of optical microscopy (OM) are well known and often used for the examination of fibers and yams from archaeological textiles. Many texts provide the fundamentals of the technique (e.g. 40-43). Some manuscripts describe the methods that may be employed in the study of archaeological materials in particular (44, 45), while others report the results of optical microscopic examination in identification and characterization of archaeological fibers (e.g., 12, 46). 

Lab grade hematite (Fe203) and copper sulfate (anhydrous and hydrated) were mounted on slides and used as controls to compare to mineral deposits that might have been found adhering to foe fibers. Rabbit hair and milkweed that had been colored with an aqueous hematite solution and with an aqueous copper sulfate (blue vitriol) solution were also used for comparison. Fibers removed from each simulated material were mounted in water (Refractive Index (Rl) of 1.0), and in Permount (Fisher Scientific) (RI of 1.55). The collected particulate matter and fibers removed from foe yam samples were similarly mounted and examined using optical microscopy. 

Glass. Packages of 200 filament strand pulled from a standard E glass composition were provided by PPG Industries. Density p was taken as 2.55 g cm-3 fiber diameter d measured by optical microscopy ranged from 8.9 to 9.1 pm. 

In testing the SFC specimens, acoustic emission (AE) was monitored while the specimens were strained, by counting AE events and recording the energy associated with the events. In combination with optical microscopy, it was of interest to identify the correspondence between AE events and fiber fragmentation. The first results along these lines are also reported. 

There are many examples of second-order analyzers that are used in analytical chemistry including many hyphenated spectroscopic tools such as FTIR-TGA, IR-microscopy, as well as GC-MS, or even two-dimensional spectroscopic techniques. Another hyphenated technique that is being developed for the study of solid-state transitions in crystalline materials is dynamic vapor sorption coupled with NIR spectroscopy (DVS-NIR).26 DVS is a water sorption balance by which the weight of a sample is carefully monitored during exposure to defined temperature and humidity. It can be used to study the stability of materials, and in this case has been used to induce solid-state transitions in anhydrous theophylline. By interfacing an NIR spectrometer with a fiber-optic probe to the DVS, the transitions of the theophylline can be monitored spectroscopically. The DVS-NIR has proven to be a useful tool in the study of the solid-state transitions of theophylline. It has been used to identify a transition that exists in the conversion of the anhydrous form to the hydrate during the course of water sorption. 

Applications of fiber-optic pH sensors in environmental analysis, biomedical research, medical monitoring, and industrial process control have been reviewed by Lin [67]. A multitude of luminescent systems for pH monitoring are commercially available, mostly under special trademarks. Pyrene [68-70], coumarin, bromothymol blue [71] and fluorescein [72-74] derivatives are typical examples that have been used in research in the past two decades. Carboxyfluorescein derivatives have been directly applied to skin tissue samples for the lifetime imaging of pH gradients in the extracellular matrix of the epidermis [75]. Two-photon excitation microscopy became an estab-... 

The term probe or proximal probe used in this document refers to any of die wide variety of tips used in tunneling, force, and near-field optical microscopies. That is, a metallic, semiconducting, or optical-fiber probe is positioned in close proximity to a sample for die purposes of recording images. 

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