We present a technique to perform noninvasive, spatially- resolved measurements on low pressure, subsonic, laminar gas flows using Raman spectroscopy. From the Raman signal, the density and temperature conditions of the flow can be extracted directly, with reasonably low integration times. The use of a high power laser diode adds to the simplicity of the measurement, plus it makes it a very attractive low cost, efficient technique. Temperature regimes studied are from 290 K - 725 K, spatial resolution obtained is approximately 2.5 X 1.5 mm² in the flow cross section, and 10-30 micrometers in the flow direction, within a flow profile of diameter approximately 1.5 cm. The flow was generated by a conical double nozzle system with CO₂ at the center and Ar as sheath gas. The goal of the measurements is to study the gas dynamical focusing obtained, which will be used for future experiments on highly nonvolatile compounds.

During the past decade Raman spectroscopy has moved out of the shadow if IR spectroscopy and has become a routine laboratory tool for chemical analysis. This is largely due to the development of stable diode lasers, fiber optic samples probes, compact optical designs, high quantum efficiency detectors, and personal computers with fast electronics, and associated data acquisition and analysis. These developments allow real-time, multi-component chemical analysis, and suggest the use of Raman spectroscopy for process monitoring and control. Single-ended fiber optic proves simplify coupling into process streams, allow remote placement of the Raman instrument from the sample point, and give Raman spectroscopy a decided advantage over IR spectroscopy in industrial liquid and solid process applications. Indeed, more than a dozen new Raman instrument companies offering fiber optic based systems have been launched in the past five years. Notably, all of these systems employ charge coupled device detectors. And yet, only one company has successfully penetrated the industrial market. Instrument limitations cited include fluorescence interference, incomplete spectral coverage, wavelength reproducibility, and long-term instrument stability. To address these limitations, Real-Time Analyzers has developed a Fourier transform Raman instrument. It employs a diode pumped Nd:YAG laser with excitation at 1064 nm and a single element, uncooled InGaAs detector, that are integrated into On-Line Technologies' proven rugged, vibration and temperature immune interferometer. Instrument design and industrial applications will be presented.

As Raman spectroscopy finds increased utilization for on- line measurement, the issues of analyzer stability and calibration transferability grow in importance. This paper present a method that allows calibrations developed on one analyzer to be transferred to others located at the same or different sites. This method also allows maintenance of calibrations in a single Raman analyzer over time even when critical components are altered. Calibration transfer eliminates the need to develop calibrations for different analyzers and upon analyzer repair, saving time and money in calibration model development and maintenance.

InGaAs photodiode arrays have been developed to 'cover' the SWIR wavelength range in spectroscopy. Hybridized Si/InGaAs linear arrays have become the detector of choice for remote sensing. Device 'long' wavelength spectral performance is achieved by rearranging the photodiodes In/Ga stoichiometric ratio. However, increased long wavelength response adversely affects deice characteristics. The self-scanned InGaAs linear array mechanical and opto/electronic properties will be discussed.

Foster-Miller has leveraged its innovations in IR fiber- optic probes and the recent development of a miniature spectrometer to build a novel IR sensor system for process applications. The developed sensor systems is a low-cost alternative to process FTIR and filter based systems. A monolithic wedge-grating optic provides the spectral dispersion with low cost thermopile point or array detectors picking off the diffracted wavelengths from the optic. The integrated optic provides spectral discrimination between 3- 12 micrometers with resolution at 8 cm^-1 or better and high overall optical throughput. The device has a fixed cylindrical grating uniquely bonded to the edge of a ZnSe conditioning 'wedge'. The conditioning optic overcomes limitations of concave gratings as it accepts high angle light at the narrow end of the wedge and progressively conditions it to be near normal to the grating. On return, the diffracted wavelengths are concentrated on the discrete or array detector elements by the wedge, providing throughput comparable to that of an FTIR. The miniature spectrometer coupled to flow through liquid cells or multipass gas cells provides significant cost advantage over conventional sampling methodologies. Currently, we are investigating process applications for the petroleum and dairy markets. The sensor system eliminates the cost, complexity, reliability and bandwidth/resolution problems associated with either Fabry Perot or Michelson Interferometer based approaches for low-cost process applications.

Near-IR spectroscopy is the analysis of the light absorption and transmission characteristics of materials in the wavelength region extending from approximately 800 nm to 2500 nm, lying between the conventional mid-IR region at longer wavelengths and the visible region at shorter wavelengths.

In a Department of Energy funded project, a low resolution Fourier Transform IR Continuous Emissions Monitoring (FTIR CEM) and Process Control system was developed and evaluated for use in minimizing HCl emissions during aluminum casting operations. In the casting process, molten aluminum is treated by fluxing with chlorine to remove alkali and hydrogen impurities. The industry has traditionally used a stoichiometric excess of chlorine to ensure metal quality, with resulting atmospheric emissions of HCl. The FTIR system can potentially be used to reduce emission when employed as a closed-loop process control device to monitor the HCl concentration and thereby reduce chlorine usage while maintaining product quality. In the initial project phase, tests were conducted under varying process conditions at a pilot-scale casting facility. The goals of these test included demonstrating that the FTIR monitor could provide closed-loop control of chlorine use, correlating HCl emission with metal quality, and verifying that the instrumentation could operate under harsh casting facility conditions. The system will subsequently be tested at two aluminum production facilities. This paper summarizes the results from the initial evaluation of the FTIR CEM/Process Control system.

An ellipsoid reflector was designed and machined to increase the light collection efficiency for Fourier Transform IR (FTIR) spectrometer in mid-IR region. The ellipsoid reflector is used to collect and focus the IR radiation from a Globar, then a parabolic mirror was used to generate the parallel beam as input beam for FTIR spectrometer. Experimental results showed that the ZPD value of the spectrometer with this Mid-IR reflector has increased by a factor of two comparing to typical one-mirror collecting method for FTIR. Due to the higher launching efficiency of the mid-IR reflector, the scans required to obtain a certain spectrum resolution for gas absorption spectrum with required SNR can be reduced. The best collection efficiency with ellipsoid reflectors has been calculated. The further improvement with different reflector shapes and polishing surface will be discussed. As a result, with higher SNR of FTIR, this research has gone one step further to realize real-time/on-line monitoring and control of gas concentration in a CVD chamber in reducing the monitoring time.

Precision industrial gas sensor which operate at room temperature and pressures in the 100-1000 mbar range are simulated by using the characteristics of DFB GaAs/Sb based tunable diode lasers operating in the 1-5 micrometers band within a simple optical bench having an absorption path length of 1-5 cm and by using the Fourier transform absorbance ratio digital analysis and control methods to achieve resolutions in the sub ppmv range for gas mixtures. The direct detection absorption spectroscopy theory, methods and sensor structure are reviewed and newly developed analysis and control noise models are presented. Absolute precision in terms of gain accuracy and resolution relationships is presented for these methods. Simulation methods for the error terms are also presented. Digital simulation results on rejection of noise, fringes, laser power function and interference lines for H₂O and CO₂ sensor at selected wave numbers are presented.

Future gas turbine combustor designs for aerospace applications will be required to meet severe restrictions on environmentally harmful emissions. To meet the target emission reduction goals, these combustors will operate at temperatures and pressures greatly exceeding those of present day aero-powerplants. New diagnostic methods are required to provide insight into understanding the complex physical and chemical processes extant at these conditions because traditional diagnostic methods are either insufficient or incapable of providing this knowledge. At NASA Glenn Research Center (GRC), several optically accessible combustor rigs have been built which allow the implementation of a suite of optical diagnostic techniques that are capable of providing just this type of crucial information. The techniques employed in the GRC combustion research laboratory include planar laser-induced fluorescence and planar Mie scattering. Research efforts have been quite successful probing both non-reacting and reacting flowfields of many kerosene-fueled combustor and combustor subcomponent design at pressures approaching 2.0 MPa, and temperatures near 2100 K. Images that map out combustion intermediate species such as OH distribution, fuel spray patternation, and fuel to air ratio contour mapping have been obtained for many different fuel injector designs and configurations. A novel combination of multiple planar images and computational analysis allows a 3D capability that greatly enhances the evaluation of the combustion processes and flowfields examined in this study.

Conventional solution-phase chemical synthesis involves a number of discrete synthetic steps from which intermediates and products are isolated for characterization at the completion of each step. In solid-phase synthesis, intermediates are linked to a solid support and are not removed until the product is isolated at synthesis completion. This approach facilitates the removal of unwanted by-products and maximizes yield. Solid-phase synthetic procedures typically suffer form a number of drawbacks including the use of large excesses of reagents to drive reactions to completion, long reaction times, and large volumes of solvent washes required to remove unreacted reagents between steps. This work describes the use of spectroscopic techniques to optimize solid phase synthesis by making measurements in both the solid and liquid phases. These measurements can lead to faster processing times, reduced chemical waste, and a reduction in the amount of reagents used. 4

Cost-effective and environmentally-sound means of paint and coatings removal is a problem spanning many government, commercial, industrial and municipal applications. For example, the Department of Energy is currently engaged in removing paint and other coatings from concrete and structural steel as part of decommissioning former nuclear processing facilities. Laser-based coatings removal is an attractive new technology for these applications as it promises to reduce the waste volume by up to 75 percent. To function more efficiently, however, the laser-based systems require some form of process control.

In this work, a fiber optic sensor based on Fresnel principle is presented. It is used to monitor the variations of the refractive index due to the cure process of an epoxy based resin. These materials are widely used in polymer- matrix composites. The process of thermoset matrix based composite involves mass and heat transfer coupled with irreversible chemical reactions inducing physical changes: the transformation of a fluid resin into a rubber and then into a solid glass. To improve the quality and the reliability of these materials key points are the cure monitoring and the optimization of the manufacturing process. To this aim, the fiber optic embedded sensor has been designed, developed and tested. Preliminary results on sensor capability to monitor the cure kinetics are shown. Correlation between the sensor output and conversion advancement has been proposed following the Lorentz-Lorenz law. Isothermal data form the sensor have been compared with calorimetric analysis of an epoxy based resin.

The present paper describes an Open Path Electro-Optical Gas Monitoring System specifically designed for in-situ on-line monitoring of flammable and toxic atmospheres in the Printing Industry in general, and for air-duct applications in particular. The printing industry posies unique fire hazards due to the variety of toxic and flammable chemical employed in the various printing process. Flammable material such as paper, ink, solvents, thinners, metal powders, cornstarch powders, cloth, synthetic materials are frequently used in the printing industry in several processes such as letter-pressing, lithography, screen printing etc.

On-line real-time monitoring of the gas-phase concentrations of sulfur containing molecules such as sulfur dioxide (SO2), hydrogen sulfide (H2S), carbon disulfide (CS2) and nitrogen containing molecules such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O) and ammonia (NH3) is of major importance in pollution monitoring and reduction and in the optimization of many gas-phase industrial processes. A UV optimized non-solarizing fiber-optic based diode-array analyzer system utilizing a 10,000 hour MTBF Xenon pulsed source has been developed and proven on-line. An on-board chemometric prediction engine allows for the simultaneous multi-component analysis of measured spectra of sample gases in real-time. Fiber-optic coupling of the analyzer to the gas flow cell housed within the sampling system allows intrinsically safe measurement to be carried out on samples gases at temperatures up to 310 C and pressures to 60 barg. Detection sensitivity down to ppm levels have been realized including such measurement applications as NH3, NO and H2S monitoring.