The ability of Fourier transform infrared spectroscopy to perform in-situ measurements of ferroelectric thin film properties during metalorganic chemical vapor deposition is demonstrated. Infrared measurements of film reflectance and radiance allowed determination of film composition, thickness and temperature in real-time. These spectra could also be used to follow process changes, determine deposition rate, and extract the wavelength dependent dielectric function. These data, along with computer software and optical hardware developments, are presented.

The FT-IR system K300, primarily used for environmental monitoring by means of remote sensing techniques, has been modified in such a manner that it could be used for remote monitoring of a SiC chemical vapor infiltration process (CVI). This comprised hardware adaptations to a CVI reaction plant at DASA (MBB), as well as development of analytical methods. First measurements showed the good performance of the K300 system at the reactor. A lot of gaseous species could be detected and qualitatively analyzed (concentration changes).

Quasi-chemical model for ZnSe properties control has been elaborated and confirmed by the photoluminescent measurements. Origin of native defects in ZnSe:Se has been developed.

FT-IR process analyzers have been successfully installed on hundreds of processes around the world. Often streams analyzed are very complex multicomponent systems. Easy applications don't tend to be solved by FT-IR, easy applications get solved by less expensive technology. But the speed and low maintenance offered by on-line FT-IR analyzers attracts the attention of process people looking for a better way to control their plant. This paper describes applications in specialty chemicals, polymer production, and refinery production which demonstrate the range of techniques used to appropriately calibrate the on-line analyzer. Calibration transfer issues from lab to on-line analyses are discussed.

For years, near infrared spectroscopy has been aggressively promoted and successfully used as a quantitative tool for accurately measuring parameters of remarkably varied materials. Using sophisticated statistical software, the instruments extract correlations between a measured absorbance signal in the spectrum and the property or concentration of interest. From food products to gasoline octane, NIR has been demonstrated to perform well, but nagging reliability and calibration issues persist. Using Fourier Transform techniques in the NIR largely eliminates vexing problems the dispersive units suffer. FT-NIR analyzers offer the same sampling and software capability, but add reliability and stability to the measurement. This paper details several applications of process FT-NIR to complex quantitative analyses in industry and describes recent improvements in fiber optic sampling tools which have further advanced the role of FT-NIR for on-line analyses.

This paper describes the use of Fourier Transform Infrared (FT-IR) spectroscopy coupled with an Attenuated Total Reflectance (ATR) accessory to quantify the individual sugars (glucose, maltose, maltodextrins...) in a mixture extracted from a process of wheat transformation into sugar. ATR accessory allows us to analyze very viscous media such as molasses by pouring the medium on a flat crystal. In the first step, model mixtures are prepared in the concentrations common to sugar industries and are analyzed by an FT-IR spectrometer. Binary (glucose/maltose) and ternary (glucose/maltose/maltotriose) solutions are used. Spectra are recorded from 1300 to 850 cm^-1. Multivariate mathematical processing methods are applied to these spectra (Partial Least Squares and Principal Component Regression). The results show a very good discrimination between the different sugars.

A novel spectrograph configuration, ideally suited for process control applications, is discussed. The configuration, referred to as axial transmissive, consists of axially-symmetric refractive optics and a volume phase holographic transmission grating. The axial transmissive spectrograph is very compact and robust, featuring no moving optical elements. This configuration also results in very high spatial resolution, allowing a large number of different processes to be monitored simultaneously on a single 2-D array detector. Results are presented for experiments, performed using the axial transmissive spectrograph with a laser, fiber optic sampling, and a multi-channel CCD detector, that are representative of process control applications.

Transuranic (TRU) and low-level drum waste disposal involves decisions based on transportation restrictions, conditions for acceptance, and federal and state regulations. To support the decisions made concerning final disposition of these wastes, characterization protocols must be established to help define the environmental impact. One promising screening technique involves applying near infrared (IR) Fourier Transform Raman (FT- Raman) spectroscopy using remote fiber optic probes for identifying unknown salts, sludges, and solids in wastes. It is proposed that FT-Raman spectroscopy be used in conjunction with real-time radiography and visual documentation. Developing an extensive solid waste library is a key element in the deployment of this technology in the process environment of solid waste drums. The feasibility for such library generation is also demonstrated.

Polymer dye films incorporating a pH indicator, immobilized on a polymer support, can be used for ammonia gas (NH₃) sensing in fiber optic and portable instruments in the field operating conditions with changing temperature and humidity. Experimental results on the NH₃ detection in the range 0 - 100 mg/m³ are reported for the range of temperature 25 - 45 degree(s)C and 60 - 80% relative humidity. A model of steady-state instrument response in the field has been developed with four adjustable parameters to describe the coupling of ambient NH₃ concentration to absorbance change of the sensing element. Practical problems associated with the applications of such sensing chemistry for NH₃ monitoring in the field are discussed.

The addition of stabilizers such as hindered phenols, phosphites, hindered amines, and benzotriazoles to polyolefins provide protection from oxidation due to heat, light, or stress. The level of stabilizer in a polymer is related to polymer performance from the time of processing throughout the polymer's lifetime. As a result, measurement and control of the additive concentration that is melt compounded into the polymer is crucial. Making these measurements in the melt offers many advantages over current off line quality control methods such as GC and HPLC. This paper discusses the on-line method for monitoring the levels of hindered phenols and phosphites in polypropylene. This method is based on UV spectroscopy coupled with fiber optics. Data are presented to show the successful measurement of these additives even in the presence of potential interferants.

This paper briefly describes the fabrication of infrared light emitting diodes by liquid phase epitaxy including both InGaAs LEDs for emission wavelengths from 2.5 to 3.8 micrometers and InAsSbP for wavelengths from 3.8 to 4.7 micrometers . Some of the first applications of these LEDs in spectroscopic instrumentation are described together with the main instrument characteristics. Nondispersive analyzers have been developed for CH₄ and CO detection utilizing LED sources emitting at 3.3 and 4.7 micrometers , respectively. A novel infrared spectrometer construction has been developed based on a linear LED array emitting at 3.3 micrometers and a fixed grating monochromator. This miniature construction can be used as an electrically scanned spectrometer module in future IR analyzers for portable and process on- line applications.

Polymeric materials, specifically polyurethanes, have been investigated with the use of mid- infrared transmitting fibers. The fibers are used as internal reflection elements for attenuated total reflectance (ATR) spectrometry. Fourier transform infrared (FT-IR) spectrometers were used to collect the data. Spectra were collected at rates of three spectra per second to 5 seconds per spectrum. The spectral bandpass of the systems was from approximately 5500 cm^-1 to 850 cm^-1. Not only was the reaction chemistry monitored, but chemical morphological changes were recorded as well. Water slabstock polyurethane foams were studied as were reaction injection molded (RIM) polyurethanes.

The development of new infrared transmitting optical fibers with low optical losses, sufficient mechanical strength, and temperature range to meet the demanding conditions of many process environments -- and the availability of improved, ruggedized low-cost FTIR spectrometers -- have made in situ FTIR measurements possible. This paper discusses the development of a mid-IR tapered infrared transmitting optical fiber for monitoring the cure of epoxy resins.

The development of diagnostic instrumentation for monitoring coal liquefaction process streams is discussed. A sapphire optical fiber was used as an attenuated total reflectance (ATR) element in conjunction with Fourier transform infrared (FT-IR) spectrometry to probe harsh liquefaction process streams. ATR provides a short, reproducible pathlength which allows for the analysis of highly absorbing materials, such as liquid hydrocarbons, and the properties of sapphire are well suited for the analysis of high temperature and high pressure process streams. A test cell was constructed which allowed in-situ monitoring of coal liquefaction reactions at 400 degree(s)C and 3000 psig. The cell incorporated a sapphire optical fiber as an ATR sensing element which was coupled to an FT-IR spectrometer using zirconium fluoride fiber optic cables. The spectra provide qualitative information about the liquefaction process.

Optical fiber-based Fourier transform infrared (FTIR) is investigated as an in-situ monitoring tool for two applications in organometallic chemical vapor deposition (OMCVD): measurement of the concentration of organometallic precursors fed to the system, and detection of gas-phase reactions relevant to the process. The feasibility of the first application is demonstrated using fluoride fibers in case studies with trimethylindium and trimethylgallium. With a short single pass gas-cell, a minimum detection limit of 0.5% is achieved for a one minute scan time. Further reduction in this limit may be realized by improved cell design and longer scan times. The second application of the FTIR technique, in situ monitoring of gas-phase reactions, is also demonstrated. The results are in excellent agreement with previous reported data for the pyrolysis of the two precursors.

Recently, solar furnaces have been successfully used to harden steel, coat metals, and initiate physical and chemical vapor deposition. Successful development of this technology requires process monitoring of surface temperature, which can be in excess of 2000 degree(s)C. This severely limits the accuracy of standard devices. This paper describes the use of FT-IR spectroscopy to measure spectral reflectance and radiance of solar-heated samples in order to accurately determine their temperature. The system features a fiber optic arrangement, representative of a hemispherical mirror, to collect diffusely reflected radiation. Preliminary results are given.

The quantification of chemical processes in real time using infrared fiber-remote absorption spectroscopy requires the accurate sampling of the chemical species at a well defined and reproducible absorption pathlength. Sensors and sampling methods are described which are tailored to the type of process and process conditions being monitored. The optical fiber parameters which effect process sampling and measurement accuracy are reviewed. Sampling techniques are discussed for homogeneous liquid phase and gas phase measurements. The use of flow through cells for side stream monitoring and immersible probes for in-line monitoring of liquid phase streams are covered in detail. Sensor pathlength calibration of a variable path immersible transmission probe is discussed.

The use of FT-IR spectrometers for on-line monitoring and process control has recently been gaining in popularity. Many of these FT-IR systems use LN₂ cooled detectors. This paper discusses the use of stirling cycle cryogenic coolers for the cooling of IR detectors to liquid nitrogen temperatures (77 K). The technology of linear drive coolers, using dual opposed pistons and clearance-seal technology is discussed as a method of minimizing detector microphonics while maximizing cooler durability.

At-line monitoring techniques can be used to gain better control of manufacturing processes. The result of better control is a more efficient process; one where product quality is improved and operating costs are reduced. The current study examines the reaction of phthalic anhydride, maleic anhydride, propylene glycol and diethylene glycol to produce polyester resins. The performance of the resin is high dependent on the composition. Because it is not a simple matter to charge the batch reactor with the necessary proportion of reactants, adjustments are often necessary. To reduce or eliminate the number of off-grade batches a rapid at-line mid-infrared method has been developed. The measurement can be completed in a matter of minutes and requires no sample preparation. Initial reactant charges can be determined despite the fact that the reaction has begun by the time the batch is homogeneous and can be sampled.

A laser-induced plasma is used for atomization, ionization, and excitation of elements in solid samples. The temporal and spatial behavior of the plasma is studied by observing the emission lines of neutral aluminum and magnesium. The optimal temporal choice was determined for our plasma spectrochemical analysis and a calibration curve for an aluminum-magnesium alloy was obtained.

Quasi-chemical model for ZnSe properties control has been elaborated and confirmed by the photoluminescent (PL) measurements. Origin of native defects in ZnSe:Se has been discussed.

Recent development of specialty silica and non-silica fibers in a synergy with an innovated design of fiber catheters, bundles and probes promote the growth of various fiber applications. There are three main areas of fibers usage: telecommunications, fiber sensing and laser power delivery, -- but we review briefly only the exiting area of fiber applications in remote spectroscopy.