Infrared transmitting optical fibers were combined with a Fourier Transform Infrared Spectrometer (FTIR) to perform remote quantitative gas analysis. A glass clad fluoride fiber, 1/2 meter in length, transmitted the infrared radiation to a double pass reflective gas cell, with a total pathlength of 10 cm, and a second fiber returned the absorbed characteristic spectrum back to the instrument. Methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO), were readily detected to very low concentrations in nitrogen with this arrangement. The concentration range and lower detection limit are dependent upon the absorption coefficient of each gas, the pathlength of absorption, and the available energy throughput at the detection wavelength. Carbon monoxide had the largest range of detection at this pathlength, with detection capabilities from 100 vol% to 0.3 vol% in nitrogen. Methane was detected from 15 vol% to 0.2 vol% and carbon dioxide was detected from 2.5 vol% to 0.05 vol%. From this study, it was determined that the fluoride fiber/FTIR system can be utilized to remotely detect gases effectively. Proper adjustment of the absorption pathlength will enable each gas to be detected over a broad range of concentrations.

A novel class of spectrochemical sensors for remote sensing of hydrocarbons is investigated. This class of sensors exploits the excellent near infrared transmission properties of commercial zirconium fluoride optical fibers that have only recently been available. Several different remote spectrochemical sensors are discussed which incorporate these IR transmitting fiber optics; they include a gas absorption cell, a photoacoustic cell, and an inexpensive FT-IR interface to a remote gas analysis cell. Design characteristics and experimental data on sensitivity and linearity are presented. Potential areas of application for the new class of sensors are also discussed.

An optical system has been developed which measures both fluence and spectral content of an infrared (IR) beam. The system integrates a luminescent sensor with a commercial spectrometer using a novel sensor and fiber-array system. Dysprosium-doped yttrium vanadate (YV04:Dy) is the IR-sensitive sensor. Heating, from a pulse of IR radiation, increases the sensor efficiency of excitation in selected spectral regions. This effect is exploited to produce a sensor whose luminescence, instead of quenching with absorption of IR radiation, becomes brighter. Beam fluence at each spectral line is calculated from the measured change in the sensor luminescent output and a previously established calibration. The useful range of sensitivity is approximately 0.08 J/cm2 to 2.0 J/cm2. A tiny sapphire rod positioned at each spectral channel in the spectrometer couples ultraviolet NW activation energy from an input fiber to the backside of the sensor. The same rod couples the sensor emis-sion into, an output fiber. The IR beam strikes the front of the sensor. The multi-channel fiber-array output is recorded with a streak camera and the experimental data are easily translated into spectral information from the known fiber position in the spectrometer focal plane. Sensor data have been collected for fiber lengths up to 500 meters between the spectrometer and streak camera.

Raman scattering techniques, because of the vibrational information they contain, have numerous applications in the measurement and identification of aqueous pollutants in groundwater, as well as other contaminated waters. However, the extension of Raman techniques using fiber optics to remote sensing of groundwater is not completely straightforward. Single-fiber optrodes provide the greatest signals but also large background levels. Multiple-fiber optrodes offer lower background levels but are not practical over very long distances and are not as sensitive as single-fiber optrodes. The difficulties of obtaining Raman spectra with fiber optics are discussed, and the potential techniques for overcoming the limitations of single-fiber devices are descrivbed. The results of Raman spectral measurements that were made using a dual-fiber optrode in a novel forward-scattering configuration will be presented. The possible extension of these results to surface-enhanced Raman (SER) scattering will be discussed. In addition initial results of SERS performed with optical fibers will be presented, along with a description of future directions for this research.

Chemical sensing in high temperature liquid chromatography (HT-LC) is a difficult task. In this setting, detection must be performed directly following the separation, at the column temperature, and at suitable back pressure, in order to preserve chemical information encoded by the chromatographic separation. A z-configuration flow cell with "in-situ" fiber optic monitoring of both absorbance and fluorescence has been developed and examined for HT-LC (ambient to 150 0C). The fiber optic based measurements circumvent problems and limitations associated with using commercially available instrumentation that does not function properly in the high temperature environment. Solarization of the fiber optic in the UV range was evaluated, and precautions emphasized. Refractive index (RI) dependencies and aberrations associated with making an absorbance measurement with a single fiber optic were examined and minimized by a unique detection approach using a position sensitive detector (PSD). Intensity fluctuations of the mercury-xenon lamp, initially more than 0.1% were reduced with the absorbance detector, leading to a 1 x 10-4 au detection limit (3 x rms noise level). Fluorescence quenching was also considered.

Infrared transmitting heavy metal fluoride optical fiber has been used to separate a Fourier-transform infrared (FTIR) spectrometer from a remote measurement point. Several types of remote sensors have been developed for concentration measurements. Remote transmission cells connected to fiber cables have been used to measure near-infrared spectra of liquids and gases. An evanescent-wave probe for obtaining spectra of highly scattering samples has been developed. Fiber-optic FTIR may be used to solve many problems in process monitoring and control.

An important consideration in the analysis of optical waveguide sensors (such as the fiberoptic fluorescent immunosensor) is the amount of total emitted fluorescence from the surface-bound proteins which is trapped and guided by the waveguiding structure of the sensor. In this paper we use a new Finite-Difference Time-Domain (FDTD) numerical technique to analyze the percentage of total fluorescence from surface dipoles which is coupled into the guided mode via the mode's evanescent tail.

Results of the characterisation of a quasi-distributed optical fibre chemical sensor are presented. Sensors have sections of cladding containing immobilised chemically sensitive compounds. Optical time domain reflectometry technique is used for sensor interrogation exploiting evanescent wave interactions. Responses of Cresol Red and cryptocyanine dye based sensors to alkaline and acid vapours are presented and discussed.

Evanescent wave spectroscopy at the surface of the core of a section of multimode plastic clad silica (PCS) fiber located centrally along a length of fiber is described. High sensitivity is achieved by the launching of tunneling modes. The absorbance of Methylene Blue is found to vary linearly with the exposed length of fiber core and to show a square root dependence on solution concentration over two orders of magnitude of the latter. This is attributed to adsorption of the dye on the surface of the fiber core.

The use of time-resolved fluorescence measurements is described as a means of improving the specificity of fiber optic sensors for analysis of environmental samples. Excitation of the sample is accomplished using a pulsed-nitrogen laser. The resulting fluorescence signal is coupled into the fiber and dispersed with a spectrograph over an intensified linear photodiode array. Fluorescence decay spectra are measured by time-gating the photodiode array and incrementing the time delay for successive laser pulses. A sensor system for trace transition metals is described which employs an organic indicator molecule, p-Tosy1-8- aminoquinoline (PTAQ), that forms fluorescent complexes with Zn and Cd. Data is presented in which differences'in fluorescent decay times of the Zn and Cd complex of PTAQ are used to deconvolve fluorescent signals from solutions containing micro-molar to nano-molar concentrations of the two metals. Time-resolved fluorescence measurements over fiber-optic cables have also been used to discriminate polycyclic aromatic hydrocarbons (PAHs) that cannot be resolved based on their fluorescence emission spectra. Comparison of decay times determined for selected PAHs in seawater with decay times in deoxygenated solvents suggest that it is feasible to use time-resolved fluorescence to enhance specificity of measurements in natural samples.

Prior work on fiber optic spectrochemical emission sensor (FOSES) concepts1,2 has been extended to the design and fabrication of a prototype fiber optic chemical sensor system for chlorinated compounds. The sensor performs analyte dissociation and atomic excitation via a radio-frequency-excited helium plasma. The device has been configured for field measurements of vadose-zone concentrations of carbon tetrachloride on the Hanford Reservation in southeastern Washington state. Detection and quantification of other atomic species may be achieved by varying the analytical wavelength. The sensor system design incorporates an RF excitation source; a metered, sub-atmospheric pressure helium supply system; an optical detection system; and a fiber optic umbilical to transmit analyte emissions to a central detection/data acquisition system. Sensor system design is summarized as well as performance data relating to detection limits and dynamic range.

A fiber optic chemical sensor (FOCS) has been developed for the monitoring of trichloroethylene in drinking water. The sensor is based upon refractive index changes, where the amount of light refracted varies as the analyte interacts with the coated surface. Response is specific for TCE, reversible, and can be used for monitoring TCE in the vapor or aqueous phase.

Optrodes that provide trace-level detection of trichloroethylene and chloroform with high accuracy have been developed. High accuracy is obtained by providing an internal intensity reference.

Experience at over sixteen sites containing over one hundred wells has shown the feasibility of using fiber optic systems for in situ measurement of aromatic ground water contaminants. Aromatic solvents, as well as the benzene, ethylbenzene, toluene, and xylenes (BTEX) fraction of gasoline, have been detected using a prototype field instrument. Well depths have varied from 5 m to 30 m, and limits of detection at 10 m have been in the ppb range. We are routinely using two separate clear tefzel-coated optical fibers bound in a black teflon tubing for in situ sensing of aromatic organic ground water contaminants via laser-induced fluorescence. One fiber, the excitation fiber, carries the 266 nm, 15 nanosecond, laser pulse down to the sensor. The other fiber, used for detection, carries collected fluorescence plus scattered laser light back up to the surface to the detector. Optical crosstalk has been observed to occur along the entire length of the sensor tubing. This may be due to fiber fluorescence. The fiber crosstalk is eliminated by use of a 320 nm cutoff filter in the detector optics. Black tefzel-coated fibers are also commercially available which could eliminate this potential problem. Evaluation of fluorescence emission versus concentration using serial dilution of standards shows that fluorescence lifetimes are important when evaluating different concentrations as well as in evaluation of mixtures. Minimization of signal-to-noise ratios in the detector electronics involves tuning the gate width used in measuring the fluorescent pulse, in order to include the full fluorescent signal returning from the contaminants. Field tests of the modular prototype instrument have been successful in their demonstration of the feasibility of this new technology. Results at a variety of types of sites are presented, showing the flexibility of the modular approach used in the design and operation of this new instrument.

Leaking underground storage tanks (UST's) are contaminating the ground water in many parts of the United States, thus causing a major environmental concern. The United States Environmental Protection Agency (EPA) has mandated that all UST's (both old and newly installed double walled tanks) be monitoredl. The majority of the UST's contain hydrocarbon fuels such as gasoline, jet fuel, kerosine and diesel.

Plasticized poly (vinyl chloride) (PVC) membranes containing aliphatic amines have been used to detect 2,4,6-trinitrotoluene (TNT) and other polynitroaromatics in water. Greatest stability has been achieved with Jeffamine T403, an amine that is highly compatible with PVC. The stability of these membranes to nitrogen loss has been evaluated in air and water as a function of the initial T403 Jeffamine concentration. The percentage loss of nitrogen with time decreases with decreasing initial amine concentration. Membranes that have been stored for 46 days in water still respond to TNT. Response to TNT is roughly proportional to nitrogen content in the membrane.

Laser-induced fluorescence is introduced as an analytical technique for the detection of particle-bond PAHs, which can be found as a result of most combustion processes. A quartz fiber is used to couple the light of a frequency-doubled excimer-pumped dye-laser into the sensor head. The fluorescence light is detected using collecting optics, a set of interference filters and a photomultiplier. PAHs in different forms (crystalline, in solution, as homogeneous particles and coated on NaCl particles) were investigated. Fluorescence spectra and time-resolved signals, which exhibit characteristic decay times, are presented.

A carbon monoxide fiber optic probe has been developed with a porous polymer optical fiber. The carbon monoxide sensing reagent is palladious chloride which was dissolved in the monomer solution before forming the porous polymer fiber. Other than the high sensitivity, the porous polymer fiber, made by heterogeneous crosslinking polymerization, exhibits very high gas permeability and liquid impermeability. The trapped indicator is very stable to atmosphere and enables this optical fiber probe to be used as a "chemfuse" for a carbon monoxide warning system. The porous sensing segment can be attached to regular waveguides by fiber optic couplings, therefore, it can be easily replaced. A linear response of this probe was observed for 1% to 100% of carbon monoxide in air. The temperature effect and interference from other gases with this probe have been investigated.

A fiber-optic coupled FT-NIR spectrometer was used to measure the NIR spectra of a series of extruder samples in the laboratory. The chemical composition of different sample sets were predicted from their NIR spectra using multivariate statistical methods. The instrument was also successfully used to obtain the NIR spectra of similar materials on-line at an extruder exit port.

We are analysing here particular examples of GRIN based optical sensors. GRIN matrix has been performed using four substantially different glasses based on thallium and cesium. Several solutions to matrix sensors have been debated and environmental measurements performed including shift and temperature.

A fibre-optic remote gas sensor utilising the frequency modulated spectroscopy technique is described which is capable of detecting pollutants and trace gases in the atmosphere in ppm to ppb levels with an extremely high degree of specificity. The present system allows absorption measurements of 5 x 10-3% for long pathlengths in multipass White cells and approximately 10-3% for shorter pathlengths when single-mode fibre links are employed. The use of multimode fibre links can reduce the sensitivity and accuracy of the measurements. This effect is shown to be due to the modal noise in the fibre and it is demonstrated how it can be minimised by suitable data acquisition and processing techniques. Data from a fibre-optic methane sensor is presented as an example to show the typical performance of the system.

In this paper we describe application of fiber-optic distributed temperature sensing to the process monitoring and control environment. The measurement technique utilizes a modified optical time-domain reflectometer (OTDR) arrangement, where an excitation pulse is launched into the fiber, and a temperature-sensitive property of the backscatter is analyzed as a function of time. From this information we deduce the temperature profile along the length of the fiber. The fiber itself is used as the sensor, and the temperature sensitive property measured is the spontaneous anti-Stokes Raman scattering of the fiber core material. The optical fiber is installed throughout the environment to be monitored, and temperature profiles are logged as a function of time. The fiber used is standard communication-grade, graded-index multimode fiber, although certain applications require fibers with special coatings. Typically, a 2 km loop is measured in 12 seconds to a point resolution of + 1°C (2.5 sigma) with a sample separation of 5 m. The performance characteristics of the distributed temperature measurement system are described including optical design, fiber properties, splice, connector and coiling effects. Installation design principles are discussed together with the interplay between the physical installation and the performance of the instrument. This discussion includes the relationships between spatial resolution, temperature resolution and accuracy, coil length, measurement time, and the environment. Use of distributed temperature sensing in a simulated production environment is discussed, including process capability study measurements and on-line process monitoring and control. A brief application review is also given.

Many fiber optic based chemical sensors have been described which rely on a reagent chemistry fixed at the fiber endface to provide analyte specificity. In such systems, problems involving probe-to-probe reproducibility, reagent photolability and reagent leaching are frequently encountered. As a result, calibration and standardization of these sensors becomes difficult or impossible and thus inhibits their application for long term in situ chemical monitoring. Many of these problems can be addressed and several additional advantages gained by continuously renewing the reagent chemistry. To illustrate this concept, a fiber optic ammonia sensor is described in which the reagent is delivered under direct control to a sensing volume of approximately 400 nanoliters located at the probe tip. Using an acid-base indicator (bromothymol blue) as the reagent, the sample ammonia concentrations are related to modulations in light intensity with a lower limit of detection of 10 ppb. The sensor performance was studied with respect to reagent pH, concentration and reagent delivery rate. Compared with previous fiber optic ammonia sensors, the ability to reproducibly renew the reagent has resulted in improvements with respect to response and return times, probe-to-probe reproducibility, probe lifetime and flexibility of use.

Transition metal complexes show considerable promise as luminescence probes. A brief description of the bonding and spectroscopy of this class of materials is presented with special emphasis on d6 complexes incorporating oc-diimine ligands. Principles for designing complexes with desirable properties are described and germane examples are presented.

A fluorescence based fiber optic chemical sensor has been developed to measure the concentration of dissolved carbon dioxide in sea water. The sensor configuration involves a single strand of step index multimode silica fiber, one end of which is terminated with a conical ferrule connector while the other end is incorporated with a special reservoir cell. This special cell contains a CO₂ permeable membrane at the tip. An aqueous solution of 8-hydroxy-1,3,6- pyrenetrisulfonic acid-trisodium salt has been employed as the sensing reagent. CO₂ dissolved in water permeates through the membrane into the sensing solution and alters its pH causing modulation in the emission intensity of the dye. Linear response is observed for this sensor over 0-600 ppm range. Measurements are done with a custom made filter fluorimeter.

A low cost, disposable fiber-optic based sensor, capable of in vitro and in vivo monitoring of oxygen partial pres-sure has been developed as part of a continuous blood monitoring system. The uniqueness of the sensor is its easy manufacturability. A specific length of the polymeric cladding at the fiber tip is removed and the glass core is recladded by a dipping process whereby a fluorescent dye, immobilized in a vulcanizable, gas-permeable polymer is applied. By adjusting the refractive index of the recladding material, highly efficient coupling of the fluorescent light is realized. The sensor is then coated with a reflective material to capture the fluorescent light. Signal to blank ration of > 300 is consistently achievable. Sensors fabricated in this manner are found to be durable, exhibit low susceptibilities to mechanical perturbation, and demonstrate superior response times.

Two dye-immobilization techniques on optodes are comparated ; first : adsorption of dyes on a cross-linked styrene-divinylbenzene resin ; second : ionic and adsorption binding on a hydrophilic charged polymer layer. This layer is based upon quaternized poly N-(vinylimidazole) grafted on silica fiber. The kinetics of dyes desorption, the shift of pK'a, the reproducibility of disposal probes are analyzed. A new technique of dyes coimmobilization is also explored.

Evaluation of the reproducibilities of response of optical fibre chemical sensors having either a hemispherical, or a cylindrical, tip shape was carried out. The hemispherical tip shape sensor was found to be more reproducible (s/R 7.07) than the cylindrical tip shape sensor (s/R 10%). The repeatability of the hemispherical tip shape sensor was also studied (s/R 2%). Variation in the main constructional parameters of the sensor was also investigated to determine their influence on sensor reproducibility.

A phase-resolved fiberoptic antibody-based biosensor is desci ibed, which combines the biochemical specificity of antigen-antibody reaction, the high sensitivity of laser excitation, the versatility of fiberoptic sensors, and the selectivity of phase-resolved detection. The device can differentiate benzo(a)pyrene and benzo(a)pyrene tetrol, a DNA-adduct product of the carcinogen benzo(a)pyrene. The limit of detection of benzo(a)pyrene tetrol is in the attomole range (10^-18 moles).

Usually optodes and optical enzyme sensors base on the determination of light reflected from the sensor head on an optical fiber. The fundamentals for the mathematical description of the corresponding processes are given by the Kubelka-Munk function, while in practise most commonly the Lambert-Beer-Bouguer's la w is applied. The response of a pH - optode with phenol red as indicator can be described by so-called 'F-diagrams' derived from the Kubelka-Munk function, however, the evaluation of the reflection measurements by the Lambert-Beer-Bouguer's law also leads to satisfactory results. This can be explained by the existing (pseudo-) linearity between the quantities (F), and Ax) of both theories. The application of this pH-optode in enzyme sensors for urea and penicillin G results in linear calibration curves in the case of a fluoresceine based electrode non-linear calibration curves are obtained.

We describe a new biosensor for monitoring the concentration of enzyme glucose, lactate, and other substrates that are metabolized by an oxidation process. The method is based on the finding that enzymes having FAD as a prosthetic group change their fluorescence during interaction with a substrate. Typical enzymes that have been studied include glucose oxidase (GOD), lactate mono-oxygenase (LMO), and cholesterol oxidase (ChOD). Their fluorescence is monitored via fiber optic light guides at wavelengths above 500 nm, following fluorescence excitation at around 410 - 450 nm. The relative fluorescence intensities of the enzymes vary to a large extent, being highest for LMO, and rather low for ChOD. Typical detection limits are in the 0.5 mM range for lactate and 1.5 mM for glucose at ambient oxygen pressure. A characteristic feature of this sensor is the narrow dynamic range which usually does not exceed 3 mM. This can be explained in terms of enzyme kinetics and diffusional processes. Unlike optical biosensors based on measurement of the intrinsic fluorescence of NADH, this sensor type has the advantages of full reversibility (because reduced FAD-based enzymes accept oxygen as a second substrate) and analytical wavelengths that are compatible with plastic or glass fiber optics. It is fairly simple in construction because the enzyme acts as both the recognition and transduction element. The method also has been applied successfully in an flow injection analysis-like type of arrangement.

Breath-by-breath monitoring of the partial pressure of oxygen is the main interest for the development of a fast responding optical oxygen sensor. Monitoring the P02 finds its main interest in critical care, in artificial respiration, in breath by breath determination of respiratorial coefficients and in pulmonarial examinations. The requirements arising from these and similar applications are high precision, high long term stability, and time constants in the range of less than 0.1 sec. In order to cope with these requirements, we investigated different possibilities of fast P02-measurements by means of optical sensors based on fluorescence quenching. The experimental set up is simple: a rigid transparent layer is coated with a thin layer of an hydrophobic polymer which has a high permeability for oxygen. The oxygen sensitive indicator material is embedded into this polymer. An experimental set up showed time constants of 30 milliseconds. The lifetime is in the range of several months. Testing of our test equipment by an independent working group resulted in surprisingly good correlation with data obtained by mass spectroscopy.

Rapid development of fiber optic sensing technology promises better devices for medical practice. In this paper, a new fiberoptic catheter-tip blood pressure transducer is presented. During measurement, pressure is applied through a side port to a cantilever structure to cause a combined linear and angular displacement of the optical fibers with respect to a fixed reflector, thus modulating the input carrier light. At the signal processing module, a signal proportional to the applied pressure is generated. Factors affecting the performance of the new transducer have been carefully examined during its development and are discussed. In-vitro experimental results have demonstrated the promising performance of this transducer. It is capable of direct blood pressure measurement for assessment of cardiac and arterial functions.