Tunable Diode Laser Absorption Spectroscopy (TDLAS) is finding ever increasing utility for industrial
process measurement and control. The technique's sensitivity and selectivity benefit continuous
concentration measurement of selected analytes in complex gas mixtures. Tradeoff options among optical
path length, absorption linestrength, linewidth, cross-interferences, and sampling methodology enable
sensor designers to optimize detection for specific applications. This paper describes TDLAS measurement
precision and accuracy limitations in emerging applications that demand increasing volumes of distributed
miniaturized sensors at diminishing costs. In these situations, the TDLAS specificity is a key attribute,
while high sensitivity enables novel sampling package designs with short optical pathlengths. Under these
circumstances, the traditional approaches to optimizing accuracy and precision may fail if analyzer control
features are sacrificed to reduce cost. We describe here a relatively simple TDLAS sensor designed to
meet the needs for acceptable cost, and discuss its theory of operation along with the implications on
measurement accuracy and precision.
This paper reports the development and initial testing of a field-portable sensor for monitoring hydrogen peroxide (H2O2)
and water (H2O) vapor concentrations during building decontamination after accidental or purposeful exposure to
hazardous biological materials. During decontamination, a sterilization system fills ambient air with water and peroxide
vapor to near-saturation. The peroxide concentration typically exceeds several hundred ppm for tens of minutes, and
subsequently diminishes below 1 ppm. The H2O2/ H2O sensor is an adaptation of a portable gas-sensing platform based
on Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology. By capitalizing on its spectral resolution, the
TDLAS analyzer isolates H2O2 and H2O spectral lines to measure both vapors using a single laser source. It offers a
combination of sensitivity, specificity, fast response, dynamic range, linearity, ease of operation and calibration,
ruggedness, and portability not available in alternative H2O2 detectors. The H2O2 range is approximately 0- 5,000 ppm.
The autonomous and rugged instrument provides real-time data. It has been tested in a closed-loop liquid/vapor
equilibrium apparatus and by comparison against electrochemical sensors.
This manuscript summarizes the effort to develop a field- portable Fourier Transform Infrared instrument that can perform a quick and accurate chemical analysis of unknown waste materials at Air Force bases without removing a sample for analysis. We report that devices containing a novel infrared fiber optic sensor can remotely detect and quantify the range of liquid hazardous waste typically found at Air Force bases.
In pharmaceutical manufacturing, it is critical to determine the cleanliness of the reactor walls prior to the blending/formulation process. A remote non-contact, real- time reflectance probe was developed to monitor these cleaning procedures. It utilizes the principals of IR spectroscopy and it works in the mid-IR region, as the ability to obtain spectral information in the mid-IR region not only enables this probe to monitor processes like reactor cleaning, but also to identify contaminants based on their spectral fingerprints. The spectral data can then be compared against-pre-existing calibrations or spectral libraries to determine surface cleanliness or to identify contaminants. This manuscript will discuss the design principles of the probe and present data obtained in actual tests. The non-contact reflectance probe is certainly not limited to its application for determining the cleanliness of reactor walls. Such a probe would find numerous applications in process monitoring and as a research tool for surface analysis and characterization.
This manuscript summarizes the effort to demonstrate the feasibility of developing a field- portable Fourier transform infrared (FTIR) instrument that can perform a quick and accurate chemical analysis of unknown waste materials at Air Force bases without removing a sample for analysis. We report that devices containing a tapered infrared fiber optic sensor can remotely detect and quantify the range of liquid hazardous waste typically found at air force bases. Partial least squares (PLS) calibration equations were formulated and shown to accurately predict the concentration of components in a mixture with an error of +/- 0.05% volume.
This manuscript summarizes the effort to demonstrate the feasibility of developing a field-portable Fourier Transform Infrared (FTIR) instrument that can perform a quick and accurate chemical analysis of unknown waste materials at Air Force bases without removing a sample for analysis. We report that devices containing a tapered infrared fiber optic sensor can remotely detect and quantify the range of liquid hazardous waste typically found at Air Force bases. Partial Least Squares (PLS) calibration equations were formulated and shown to accurately predict the concentration of components in a mixture with an error or +/- 0.05% volume.
A study of real-time in situ monitoring of the chemical states of urethane cross-linked solid rocket propellant during cure and aging using an embedded fiber optic sensor and a Fourier transform IR spectrometer is presented. The aging study focused on the monitoring and identification of chemical species that migrate across the propellant-insulation bondline. In this work, a short length of tapered chalcogenide fiber was used as the sensor. The segment of fiber containing the taper sensor was mounted in a temperature controlled aluminum boat to which either inert or live propellant samples were added. The spectral data collected over a six month period indicated that the equipment and sensors were suitable for monitoring the degree of curve and contaminant migration in solid rocket propellant.
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.
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.
This paper describes initial studies that were performed to develop a personal wear badge for the accumulated exposure detection of benzene vapor. Small sections of optical fiber were coated with a membrane specific for the adsorption of benzene vapor. After exposure the fiber was placed in a Fourier transform infrared (FTIR) spectrometer and the infrared spectra of the surface bound benzene was obtained. The qualitative exposure levels were determined by peak intensities. Benzene was detected at a concentration of 100,000 ppm. Dichlorobenzene was also detectable (80,000 ppm) and could be differentiated from benzene by unique absorbance peaks. The sensor was reusable and the cumulative exposure was determined as a function of time. The sensor modifications were based on the incorporation of benzene absorbing compounds contained in a thin, high surface area porous membrane coating applied to the fiber surface. The surface coating technology was developed and demonstrated on an active fiber system. A sensor cell was designed to allow handling and direct insertion into the FTIR spectrometer.
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 FflR measurements possible. This paper discusses the development of in situ fiber optic remote FT spectroscopy and its application to the characterization of polymer resin synthesia
Polyimides possess interesting nonlinear optical properties. The overall goal of our effort is to develop the requisite synthesis and processing techniques to produce polyimides with high (Chi) (3) and low absorptive losses. The target value for many applications is (Chi) (3)/(alpha) equals 10-7 esu-cm. The synthesis and characterization of both the linear and nonlinear optical properties of these materials and the requirements for their utilization in optical bistability is reported.
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 evanescent wave in situ fiber optic remote FTIR spectroscopy and its application to assaying components of biological fluids.
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 in situ fiber optic remote FTIR spectroscopy and its application to the characterization of thin polymer coatings on substrates and the development of evanescent wave in situ fiber optic remote FTIR spectroscopy and its application to assaying components of biological fluids.
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 in situ fiber optic remote FTIR spectroscopy and its application to the characterization of thin polymer coatings on substrates.
Nonlinear optics (NLO) is increasingly important for a variety of military and commercial needs ranging from new types of laser weapons to fiber optic communications networks, to optical computing applications. Rapid advances in optical phase conjugation, optical switching, and logic have demonstrated the enormous potential for practical applications with concurrent fast-paced materials development. The research has established that polyimides potentially have the excellent intrinsic properties and tailorability to meet the requirements of a wide range of nonlinear optical devices. The research described in this manuscript is a multidisciplinary effort to target key applications and material and processing requirements for these polymers. It discusses the synthesis, characterization, and processing of the nonlinear optical properties of polyimides which have been tailored for nonlinear optical activity.
The real-time in situ monitoring of the chemical states of epoxy and polyimide resins were investigated during cure using an embedded fiber optic sensor and a Fourier transform infrared spectrometer (FTIR). In this work a short length of sapphire fiber is used as the sensor for monitoring the cure of the epoxy, while for the polyimide resin, we use a chalcogenide fiber as the sensor. The cure of the epoxy resin/graphite fiber composite is monitored in an autoclave, while the cure of the polyimide resin/graphite fiber composite is monitored in a high temperature press. The sapphire sensor is connected to infrared transmitting zirconium fluoride optical fiber cables which penetrate the wall of the autoclave and interface to the FTIR spectrometer. The chalcogenide sensor connects to other chalcogenide fibers which act as a transmission link to the FTIR spectrometer. The results indicate that this equipment and sensors are suitable for monitoring the degree of cure of the laminates throughout the entire cure cycle.
Nonlinear optics (NLO) is increasingly important for a variety of military and commercial needs
ranging from new types of laser weapons to fiber optic communications networks, to optical computing
applications. Rapid advances in optical phase conjugation, optical switching, and logic have
demonstrated the enormous potential for practical applications with concurrent fast-paced materials
development. Organic polymers such as rigid-rod polymers (also known as ordered polymers) and
polyimides have the excellent intrinsic properties and tailorability to meet the requirements of a wide
range of nonlinear optical devices. The research described in this manuscript is a multidisciplinary
effort to target key applications and material and processing requirements for these polymers. This
manuscript provides the framework for the applications development required for the rapidly growing
field of NLO devices from ordered polymeric materials. It discusses the characterization of the linear
and nonlinear optical properties of three materials, experimental approaches to observing optical
bistability, and the demonstration of dispersive optical bistability.
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