This paper reviews latest developments in gas detection using real-time correlation spectroscopy. The general method relies on using a gas sample in a reference cell as a matched optical filter, to preferentially detect similar absorption spectra of the same gas in a measurement cell. All variations of the method have the advantage of excellent selectivity, provided the gases have narrow line spectra, even when using broadband sources for illumination. They are also suitable for remote detection over optical fiber leads. This paper describes work in three main areas. First, work on a Stark modulation method to investigate a novel hygrometer is reviewed. Second, a multiline light source, formed by combining a broadband optical source with a Michelson interferoemeter, which contains a gas in one arm, is described. Third, the most recent progress with a complimentary-beam correlation spectroscopy detection system using either alternately chopped or intensity modulated light sources, is described. The latter methods are very simple as they allow use of a fixed reference gas cell.

The state-of-the-art of carbon dioxide fiberoptic sensing, using both steady-state and time- resolved luminescence measurements, is briefly reviewed. Particular emphasis is given to the authors' own research on carbon dioxide optical monitoring via an excited-state proton transfer to luminescent ruthenium (II) chelate complexes. This kind of pH transduction chemistry allows for determination of the analyte in gas or liquid phase using both emission intensity- and lifetime-based optodes using the technology (sources, detectors, electronics) already developed for optical fiber oxygen sensing. Relevant factors that affect the performance of CO₂ luminescent optosensors, such as the structure of the indicator dye, the immobilization procedure and support, the internal buffer of the sensitive layers and the working principle, are discussed as well. Finally, some recent applications in the authors' laboratories to fiberoptic carbon dioxide monitoring in spring water samples are presented.

A family of indicators has been developed for measuring different analytes, all the indicators being derivatives of the same chemical compound and having identical spectral and lifetime properties. The indicators show an absorption accessible to low-cost light sources, a large Stokes shift, and a long fluorescence decay time. All indicators can be excited at the same excitation wavelength, monitored at the same emission wavelength, and measured within the same time range. This opens the possibility for a compact lifetime-based instrument for water monitoring.

Progress towards a distributed optical fiber fluorosensor for pH is reported. The operation of the sensor is based on the pH dependent quenching of fluorescein dye immobilized in the porous cladding of a PCS optical fiber which has been stripped and reclad in a sol-gel coating. The analyte distribution is recovered from the OTDR response of the system to a short excitation pulse.

Interferometric principles have gained wide acceptance in the field of chemical and biochemical sensing. Reflectometric interference spectrometry sensors using white light multiple reflections at thin layers, structures of polymers, or monolayers of biochemicals are discussed in a survey. These are compared to other techniques, especially methods using surface plasmon resonance and grating couplers. Applications in the area of environmental monitoring in public safety are given, demonstrating the results for halogenated hydrocarbons in air and water as well as pesticides in ground water. Calibration curves, limits of decision, of detection, and of determination are specified and discussed with respect to EU limits. The application of multivariate data analysis is considered including artificial neuronal networks for multisensor systems and referencing in the case of gas sensors.

An optical fiber laser-doppler system has ben developed to detect both the laser-induced- fluorescence (LIF) signal and the laser doppler signal of phytoplankton traversing through a measurement volume. From the two measurement, the size distribution, concentration, biomass, and the amount of chlorophyll present can be determined. Our apparatus have demonstrated successfully that it can resolve distinctly the size distribution of two species of phytoplankton (Chlorella and Scenedesmus). For phytoplankton, these two species do not have mark differences in size, one being less than 10 micrometers while the other is approximately 25 micrometers , and yet our measurement gave very satisfactory results. The result obtained clearly indicates that our optical system can produce accurate and liable size measurement and is suitable to be further develop into a practical in situ field instrument.

We present requirements, analysis, and comparison of available measurement systems designed or potentially appropriate for measurement of induced electric and magnetic fields generated by hand held transceivers in lossy bodies. This comprises thermocouple, diode- dipole, diode-loop probes, pyroelectric and Hall effect sensors, and optical sensors. It has been shown that optical sensors are the best for near fields measurements in lossy bodies. This comes from their dielectric and passive nature, and hence small field perturbation. They offer possibility of field measurement in a wide frequency (up to several GHz) and dynamic ($GT 100 dB) range. These sensors also provide a good compromise between the sensitivity and spatial resolution, with the possibility of further improvement by utilizing integrated optic technology.

Immunoanalytical techniques represent one of the most important applications of biomolecules in analytical procedures. Direct monitoring of immunoreactions by a device is a particular attractive approach to environmental sensing as it offers speed, a simple test scheme, and does not require labelled compounds. Target limits of detection for pesticides are imposed by the EU drinking water act (0.1 (mu) g/1 for a single pesticide). A competitive test format with surface immobilized antigen is common for pesticide detection with direct immunosensors. Free pesticide binds to antibody in solution decreasing the amount of antibody binding to the transducer. A prototype atrazine sensor based on reflectrometric interference spectroscopy was investigated. The slope of the binding curve was used to measure the pesticide concentration by comparison with a calibration curve. By sophisticated surface modification techniques and protolytic regeneration of the surface with an enzyme we were able to use a single chip for more that one hundred measurements without significant loss of binding efficiency. Using a flow injection system a test cycle including measurement and regeneration is done within fifteen minutes. Using on-line evaluation the result is achieved five minutes after the measurement was started. Atrazine concentrations in the lower and sub-ppb range were measured in natural water samples in France. Using HPLC as a reference method, the correlation coefficients between the two analytical techniques were investigated.

A multichannel fiber-optic combustion pressure sensor system is described dedicated to parametric emission monitoring systems (PEMS) for use in natural gas-fueled, stationary, and reciprocating engines. In view of the emerging 1995 emission regulations for large stationary engines, the natural gas pipeline operators have turned their attention to PEMS' for predicting and controlling the amount of polluting emissions such as NO_x and HC. We present design considerations and performance data of a 8-channel pressure monitoring system employing fiber-optic combustion pressure sensors. The control/monitoring unit offers capabilities of sensor calibration, health monitoring, and real-time data acquisition. Using an engine position sensor trigger, the monitoring unit can calculate peak pressure, indicative mean pressure, and location of peak pressure. The system allows for 50 kHz, burst mode transfer of multisensor data to a host PC. We demonstrated performance data collected on three large-bore engines and long-term endurance test data. While initially intended for stationary engines, the system can be used in applications requiring portability including moving vehicles.

Ion sensitive fluoroprobes such as BCECF (pH) and FURA-II (Ca²⁺) are frequently used indicators for determination of ion activities in single cells and subcellular compartments, e.g. by video enhanced or video intensified microscopy. Moreover, using confocal laser scanning microscopy (CLSM) with its inherent potential for noninvasive optical sectioning of cells and tissues and subsequent 3D image reconstruction, intracellular ion topographies can be monitored via pseudocolor encoded ratio imaging from pixel to pixel enabling in vivo measurements of dynamic intracellular processes. Regardless of the degree of spatial resolution, reliable qualtitative determinations essentially depend on accurate calibration of the intracellularly entrapped fluoroprobe. Calibration is either established on the basis of a whole cell or within a more or less extended subcellular compartment and the characteristics are displayed as concentration encoded pseudocolor bar within the image frame. This calibration is assumed to be valid for other cellular compartments and, in case of ion imaging, it is even thought to be valid for every single pixel of the complete pixel field. However, the assumption of a topographically invariant intracellular calibration requires a reliable behavior of the intracellularly applied indicator. This intracellular integrity of the dyes often does not seem to exist since intracellular calibration curves considerably deviate from in vitro calibration characteristics. Deviations may be due to intracellular interactions of indicator molecules with cytoplasmic macromolecules, e.g. proteins, resulting in spectral distortions and/or sensitivity deficits as demonstrated by the indicators BCECF and FURA-RED (a FURA-II analogue) or to intracellular redistribution of the indicator as exemplified by pH measurements using carboxy-SNARF-1. Consequences of these investigations as well as further potential interferences are discussed with special respect to ion imaging techniques.

An optical reflectivity change induced by a change of the micro environment around metal island is used to construct various sensors and biosensors. To obtain a sensitive micro sensor either the island density at the surface of the sensor device or the distance of an island layer film to a solid metal surface or to another island film can be varied. Polyvinylpyrrolidone crosslinked with sulfonated bisazidostilbenes shows chaotropic ion dependent nanometric shrinking and swelling which can be observed by using this polymer as interlayer in a metal island device. This volume change of the sensing polymer is transduced to an optical signal using a metal island film, followed by a thin layer of an optically transparent welling polymer and a further metal island film as the topmost layer, exposed to the analyte. This new set-up enables the spectroscopic monitoring of the reflectance change from the backside of the sensor chip not exposed to the analyte solution. For the construction of a biosensor the device was either covered by a photo-structured polyvinylpyrrolidone membrane incorporating the desired enzymes or combined with a micro enzyme reactor. The fully reversible response of the sensor is induced by carbonate and ammonium ions liberated from urea by immobilized urease.

Imaging optical fibers can be used in conjunction with 2D detectors such as CCD cameras to fabricate array sensors. These sensors contain spatially separated photopolymers containing analyte-sensitive fluorescent indicators on an imaging fiber tip. Spatial resolution of the indicators is maintained through the imaging fiber array and projected onto a CCD detector. Sensors have been fabricated using the conventional one analyte-one sensor paradigm. This approach has resulted in multianalyte sensors for blood gases, process control parameters, and environmental contaminants. An entirely different approach is also being taken. Sensing sites containing cross-reactive indicator regions are deposited on the end of the imaging fiber. The resulting array is then challenged with a variety of analytes. Pattern recognition algorithms are employed to train a neural network. The resulting sensor array can identify subsequent challenges with the analyte even after extended use.

Biomedical fiber-optic sensors are attractive for the measurement of both physical and chemical parameters as well as for spectral measurements directly performed on the patient. An overview of fiber-optic sensors for in vivo monitoring is given, with particular attention to the advantages that these sensors are able to offer in different fields of application such as cardiovascular and intensive care, angiology, gastroenterology, ophthalmology, oncology, neurology, dermatology, and dentistry.

In order to gain wavelength and analyte flexibility, we have recently altered the transduction approach of our fluorescence-based biosensor. Briefly, binding of metal ions such as zinc to the active site of carbonic anhydrase is transduced by metal-dependent binding of a colored inhibitor to a fluorescent derivative of the enzyme; in the absense of metal the inhibitor does not bind and the label fluorescence is unquenched, but at higher metal concentrations the inhibitor binds, energy transfer occurs with moderate efficiency and the fluorescent label exhibits reduced intensity and lifetime. Inasmush as Forster energy transfer is distance dependent the position of the fluorescent label on the surface of the enzyme has some impact on the performance of the sensor. We designed, produced, and expressed site-selective mutants of carbonic anhydrase which could be unambiguously derivatized with suitable fluorescent labels, and which gave much improved responses to zinc ion compared with randomly derivatized wild type enzyme.

A novel respirometer is developed for microbial toxicity tests. The respirometer is based on luminescent quenching of oxygen to measure the concentration of dissolved oxygen in cell vessels and evaluate the toxicity of chemicals by monitoring the effect of toxicants on cell respiration of micro-organisms. The oxygen sensing element is ruthenium complex absorbed on the surface of silica particles followed by immobilizing on a silicone rubber film. The oxygen sensing film is coated on the inner bottom of a transparent cell vessel. A sensing device scanning under the cell vessel is used for remote monitoring of the oxygen concentration inside the cell vessels so that a large number of samples can be handled in one batch. The sensing device includes the excitation light sources and an optical cable connected to a filter and a photomultiplier tube for detecting the luminescence in the cell vessel which can then be related to the dissolved oxygen concentration inside the cell vessel. The movement of the sensing device and data acquisition are controlled by a personal computer. The toxicity of heavy metals to activated sludge, soil bacteria and E. coli were tested using the present device. The scanning respirometer provides a new alternative for fast and large scale screening and monitoring of toxicants using micro-organisms.

The immobilization of antibodies onto surfaces by means of a reactive polymer has been studied. Two types of surfaces, gold and titanium oxide, were investigated. After modification with a suitable reagent bearing amino group, these surfaces are able to link covalently the reactive polymer through its N-hydroxysuccinimide carbonate functions. After polymer immobilization, a reaction between antibody and the remaining reactive sites on the polymer can take palce. This permits a covalent binding of biomolecules to the surface. The resulting biosensor is stable and specific. Another approach has been used for immobilization of antibodies: it involves a modification of the polymer with sulfonate groups and fixation of tetravalent metal ions. The resulting biosensor can recognize specifically the corresponding antigen and the regeneration of the surface between polymer and antibody layers is possible.

The sol-gel process has been used to entrap pH indicators in porous glass coatings for sensor applications. This sensor is based on evanescent wave absorption using an unclad optical fiber dipcoated with the pH sensitive coating. The entrapped pH indicators show a broadening of the pH range with respect to the behavior in solution giving accurate measurement over three pH units when one indicator is used (bromophenol blue) and over six pH units (pH 3-9) when two indicators are used (bromophenol blue and bromocresol purple). The response of the pH sensor was monitored by measuring absorption at 590 nm referenced against a nonabsorbing region of the spectrum. This enabled the use of LED sources together with low cost photodiodes. The sensor displayed short response time and good repeatability. The thickness and stability of the pH sensitive coatings can be influenced by modifying the composition of the starting sol mixture. The evanescent absorption, and hence the sensitivity of the sensor, can be increased by selectively launching higher order modes in the fiber. These issues together with a full sensor characterization will be reported.

A variety of analyte-selective bulk membranes for use in optodes have been developed. They combine effectively with various optical transducers and detection techniques. Although the working principles of these membranes differ, the basic principle is a diffusion-limited exchange of the analyte between sample solution and optical bulk membrane. The thickness and viscosity of the membranes govern the diffusion and, therefore, the response time of the sensor. In accord with analytical requirements, the specifications of optode membranes can be predicted from measurements of the overall diffusion coefficients in the membrane phase. The ATR-approach is shown to be an attractive technique for such investigations.

A dissolved oxygen sensor, based on sol-gel-derived silica thin films impregnated with an oxygen-sensitive ruthenium complex, is reported. Porous sol-gel silica films, dipcoated onto either planar glass substrates or declad optical fibers, are doped with the complex [Ru^II-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence emission is quenched by oxygen. The complex is entrapped in the cage-like structure of the sol-gel matrix, but is accessible to oxygen via the microporous channels. This work compares the difference in oxygen quenching response between gas phase and aqueous phase measurements. Optimization of dissolved oxygen response by tailoring of the film fabrication parameters is reported. Using a high-brightness blue LED, combined with a miniature photodiode-based detection system, these results establish the viability of a low-cost, high-performance, portable optical dissolved oxygen sensor.

An analytical instrument comprising absorption- and fluorescence-based capillary waveguide optrodes (CWOs) is described. Glass capillaries with a chemically sensitive coating on the inner surface are used for optical chemical sensing in gaseous and liquid samples. In case of absorption-based CWOs, light from a LED is coupled into and out of the capillary under a defined angle via a rigid waveguide and an immersion coupler. The coated glass capillary forms an inhomogeneous waveguide, in which the light is guided in both the glass and the coating. The portion of the light which is absorbed in the chemically sensitive coating is proportional to a chemcial concentration or activity. This principle is demonstrated with a pCO₂-sensitive inner coating. Typical relative light intensity signal changes with this type of optical interrogation are 98%, with an active capillary length of 10 mm. For fluorescence- based CWOs, the excitation light from an LED is coupled diffusely into the glass capillary and the optical sensor layer. A major portion of the excited fluorescence light is then collected within the coated capillary, and guided to the photodiode, which is located on the distal end of the capillary waveguide. Hereby, the excitation light is separated very efficiently from the fluorescent light. As an example, a CWO for pO2 is described. By applying this optical geometry, it was possible to utilize fluorescence decay time of the sensor layer as the transducer signal even when using solid state components (LEDs and photodiodes).

Chemical sensors are analytical systems for the evaluation of compound- or ion-specific or - selective signals produced by specific or selective chemical reactions taking place at the interface between the chemically modified sensor surface and the substrate. The well known electrochemical sensing schemes have greatly contributed that sensors are considered now as the 'third supporting pillar of analytical chemistry' besides chromatography and spectroscopy. The aim of this paper is to describe the novel capabilities of chemical modified IR-transparent fibers as chemical IR-sensors for the on-line analysis of chlorinated hydrocarbons and organic compounds in aqueous solutions and gaseous mixtures, glucose, and sucrose in aqueous solution as developed in our laboratory. Moreover, the relative merits of this new method wil be depicted in comparison to other sensing techniques. Optical fiber sensors are novel analysis systems, based on molecular spectroscopy in the UV/VIS/IR-range. They benefit from the tremendous development in the field of optical fibers, an offspring of the telecommunication industry and the electronic revolution during the last few years. With the development of new materials besides the well known quartz fibers for the UV/VIS/NIR-range the optical window for fiber optic sensors was enlarged from 0,2 to 20 micrometers recently. The fiber length was increased recently to up to 2 meters for silver halides and approximately 10 meters for chalcogenides. New applications for environmental, food, and clinical sensing as well as process analysis are the driving force for modern research in IR-optical fiber sensors using mainly sapphire (Al₂O₃), chalcogenide (As-Se-Te) and silver halide (AgBr/AgCl) fibers and flow injection analysis (FIA) systems. Few representative examples for each of the various optical sensor types will be presented. Particular attention will be given to the use of silver halide fibers for the simultaneous determination of traces of chlorinated hydrocarbons in water and to FIA-systems for the process analysis of beverages.

Within the framework of this studies development of a model of a functional multicomponent highly sensitive new generation analyzer, designed to measure 2 to 4 gas components in a mixture, was proposed. This model will become a prototype for a whole new family of analyzers, which will differ from one another by their particular set of detected gases and sensitivity depending on task requirements. The gas detecting analyzers utilise the principles of high resolution absorption spectroscopy, possibly by utilising a tunable diode lasers (TDL) in the IR range. By using a laser spectral method for measuring, it ensures high sensitivity, accuracy, selectivity and fast time response in recording. The distinguishing aspect in the development of the analyzer is the design and schematic based on the use of MIR-fiber optics with low optic losses. Hence, it is possible to have the unit in a small geometric volume with instrumentation for a multichannel measuring optical track, and a simplified cryostatic system for IR lasers and photodetectors. With the help of a highly sensitive, fast tune responding analyzer based on tunable diode lasers, molecular gases, having absorption bands in the IR range, can be measured. Detection of molecules like CO, CO2, NO, NO2, N20, H2S, SO2, NH3, H20, H2O2, CH4, C2H2, C2H4, HF, HC1, HCN, freons and many others is possible using this technique. These multicomponent gas sensors can be applied as a diagnostic tool in scientific investigations, in physics, chemistiy and biochemistry, in ecology - for recording atmospheric pollutants, in medicine - diagnosing illnesses and screen tests as well as in industiy - trace chemical technology and burning processes. These systems can be also used as a reference tool for calibration of less sensitive and less precise gas analyzers used in routine monitoring.

An infrared fiber optic sensor has been developed for the in situ detection of chlorinated hydrocarbons and other pollutant species in water. The sensing element consists of a silver halide fiber, coated with an appropriate polymer. The polymer both enriches the chemical species to be measured in the evanescent wave region of the fiber and serves to exclude water from the measurement region. Evanescent wave spectrometry is then used to accurately quantify chemical species such as chlorinated hydrocarbons which have their strongest absorption bands above 10 micrometers . In order to increase the evanescent absorbance signal, and therefore the sensitivity of the sensor, a number of novel launch designs and fiber configurations has been examined. Results from a range of such configurations are presented and conclusions are drawn regarding optimum sensor design.

Investigations into the optimization of a long-path integrated optical evanescent field absorbance sensor for the detection of nonpolar organic substances in water are described. The sensor is based on a multimode strip waveguide produced by Na⁺Ag⁺ ion- exchange in a borosilicate glass substrate and a hydrophobic silicone sensing layer deposited on the IO structure, that reversibly enriches organic contaminants from water or air. Light from a tungsten-halogen lamp in launched into the planar structure and evanescent wave absorption measurements of the organic species in the silicone superstrate are performed with a near-infrared diode array spectrograph. Polymethyl(phenyl)siloxanes with varying refractive index were prepared and tested as sensitive coating for the IO structure. The light transmission through the sensor may decrease up to 90% if the coated sensors come in contact with water. These losses caused by light scattering effects due to the formation of H₂O micro- emulsions in the silicone superstrate can be minimized by using polysiloxanes with a higher degree of cross-linkage. Measurements of aqueous trichloroethene samples were successfully performed in the region of the C-H first overtone vibration band. The sensitivity of the measurement can be raised distinctively by using polymethylphenylsiloxanes, which have a higher refractive index than polydimethylsiloxane. Kinetic experiments with aqueous trichloroethene samples showed a reversible sensor response with t₉₀ values in the range from 7-20 minutes.

In this work, the main emphasis is given to the development and optimization of new fiber optic sensors for on-line gas monitoring and gas analysis. Gaseous halogenated hydrocarbons such as dichlorodifluoromethane (R 12) and trifluoromethane (R 23) have been investigated with a sensor system based on polymer coated silver halide fibers. Calibration curves down to a concentration of 0.1% have been established. Polyisobutylene, ethylene/propylene copolymer and polydimethylsiloxane have been tested according to their diffusion properties accompanied by the determination of the diffusion coefficient of gases inside the polymer layer. Particular attention is given to the application of sapphire fibers for high temperature gas sensors enabling the assignment of fiber optic sensors for the measurement of hydrocarbons like methane and butane under rough conditions. Temperature dependent calibration curves (20 to 300 degrees C) in the low percentage concentration range and the pressure dependence of the methane absorption at 3017 cm^-1 could be obtained.

A novel technique for the measurement of air flow velocity using an optical fiber sensor is reported. The sensor measures the deformation of a rubber cantilever beam when subjected to the stresses induced by drag forces in the presence of the airflow. Tests performed in a wind tunnel have indicated a sensitivity of 2 (mu) /(m/s). A qualitative model based on fiber mode propagation has been developed which allows the sensor to be characterized in terms of optical losses. A single 1 mm diameter polymer fiber is mounted on the rectangular section rubber cantilever (section 14 mm by 6 mm) and six grooves are etched into the fiber which extend into the core of the fiber. As the beam deviates the surface deforms (stretches or contracts) and the fiber is subjected to strain. As the strain is increased the grooves become wider and the amount of light transmitted through the fiber is reduced due to increased losses. The sensor described has all the advantages of optical fiber sensors including electrical noise immunity and intrinsic safety for use in hazardous environments. However, its simple construction, robustness, versatility for a number of different fluid applications, as well as relatively low cost make it attractive for use in a wide variety of measurement applications e.g. wind velocity measurement where airborne moisture or chemicals are present.

The report contains the results of the investigation of intelligent sensor dynamics. The basis here is the nonlinear controlled processes running in the reaction centers of purple bacteria and in Langmuir-Blodgett films. The quantum processes are taken into consideration, and this report theoretically explains how pollution affects the optical properties of the reaction centers. The transportation of charges is also examined. This paper presents the equation describing transformation of the water pollution data into an electrical signal convenient for processing in the cases when the adaptive Kalman filter or the neural network based on the dynamical elements are used. The report analyzes the robust characteristics of the sensor on the basis of Kalman filter. The water analysis system efficiency can be improved using the dual measurement principle suggesting identification of a biosensor model according to experimental data.

An intelligent sensor is presented, which is addressed for application in ecological monitoring. This intelligent biosensor is based on the probabilistic small-size neurochip and Langmuir- Blodgett film and its is used to detect the ecological state of industrial waters. The new concept of intelligent sensor self-organization is discussed in connection with the soliton waves moving inside Langmuir-Blodgett films.

A behavior often registered in intensity based measurements of such sensors are the downcurved STERN-VOLMER-plots, which result in problems of reproducibility and calibration, especially between different sensors of the same type. Another effect is the disagreement between lifetime- and intensity-based STERN-VOLMER-plots, which should be the same in case of dynamic quenching. For a fiber optic system with the [Ru(4.7Ph₂phen)₃]²⁺-complex in polydimethylsiloxan on the fiber tip mono- and multi-exponential decay models have been examined. There are no significant differences between monoexponential fitted lifetimes and weighted mean lifetimes from multi-exponential models. STERN-VOLMER-plots from lifetime measurements are in good agreement with intensity based measurements on fresh prepared samples.

A miniaturized fiber optical sensor based on surface plasmon resonance spectroscopy is investigated in view of the detection of organic solvent vapors, particularly tetrachloroethene. Surface plasmons are excited on a silver coated multimode fiber by polychromatic light, and the resonant excitation is detected as a resonant absorption band in the measured output spectrum. When the analyte is absorbed in a thin gas-sensitive polysiloxane film deposited on the silver layer the polymer film changes its thickness and its refractive index. These changes result in a wavelength shift of the resonant curve depending on the analyte gas concentration. Theoretical considerations about the sensing effect are made and resonance curves were computer-simulated. Based on this simulation the layout of all sensor parameters was optimized. The sensor shows an excellent response to tetrachloroethene with a response time of two seconds and high reporducibility. Using self-assembling monolayers on the silver surface a long-term stability of more than three months is obtained. The sensor shows low cross sensitivities less than 1% to other solvent vapors like aceton and ethanol, furthermore, the influence of humidity is very low. This miniaturized fiber optical sensor in combination with an easy-to-handle and non-sophisticated measuring and evaluation unit is excellently suitable for the remote sensing of special organic solvent vapors.

Photothermal phase shift spectroscopy measures the changes of the refractive index, induced by a modulated continous wave argon ion laser excitation light beam, by a double microinterferometer, consisting of an integrated optic silica chip of the sizes of 7.5 by 7.5 mm. As probe laser, a laser diode is used, which is integrated at the chip. The flow thorugh cell, containing the analyte, is mounted in one of the two arms of the Michelson interferometer between the microchip and the reflecting mirror. The great potential of this photothermal microinterferometer as a routine method for process control or environmental surveillance lies in the miniaturization of the system for the following reasons: no adjustment is needed because only fixed components are used. The quality of the light beam is significantly improved by shortening the light paths and very small sample cell volumes in the range of nl or (mu) l are needed. This has at least two distinct advantages. On the one hand, a small, compact analytical apparatus allows direct real time measurements and on site measurements. On the other hand, it is possible to built up a robust and reliable device, in one cast and without any movable part, unaffected by external influences.

An optical fiber sensor for absorption studies based on surface plasmon resonance (SPR) interrogation in the wavelength domain is proposed. The SPR wavelength is measured with high resolution which makes it possible to detect very small changes in SPR owing to the absorption of molecules onto the sensing surface. As a model case, the absorption of water molecules on silicon dioxide was studied experimentally.

In this paper we have researched the influence of pollutants made on such biological objects as photosynthesizing systems in order to reveal the capabilities and features of their application as the controlled sensor in integral ecological monitoring systems.

Valinomycin, nonactin and 1,1-dimethylsila-20-crown-7 are well known complexing agents for potassium and ammonium ions. Membrane optodes, based on these ion-selective carriers and appropriate chromoionophores, were produced and spectroscopically investigated in the range of 350-700 nm. The spectra of optodes obtained under flow injection analysis conditions were monitored in dependence on time. The calibration curves for potassium and ammonium ions were registered for each optode. The results clearly demonstrate that all tested optodes are both similarly sensitive to K⁺ and NH₄⁺. Thus, biological fluids can not be analyzed simply by the individual calibration curves when the solutions contain similar amounts of K⁺ and NH₄⁺.

The properties of polymer track membranes as a support for preparation of optrode are presented. Polyethyleneterephthalate membranes with 0.2 and 1 micrometers pores were used. The polymer foil with controlled pore size is additionally covered with poly(vinyl chloride) in order to immobilize the indicator inside the pores. The absorbance of the indicator used (N,N'-diphenylbenzidine) depends on the redox potential. The influence of different addition of covering polymer and different pore size on time characteristics of the optrode are described.

Three optically active organic indicators were evaluated for monitoring O₂, dissolved H₂S and CO. By combining a sol-gel coating with porous fiber technology, a fluorescence sensor was developed for oxygen concentrations less than 1 ppm. A second sol-gel material also possessing fluorescence properties was examined for possible H₂S sensing applications. In this instance, the fluorescence of thionin-doped, sol-gel film was quenched upon exposure to ppm-levels of dissolved H₂S. Finally, preliminary results concerning the advancement of a potential CO sensor were initialized by directly absorbing the organometallic indicator onto a porous fiber substrate. Even though the minimum sensitivity was a few percent, these results were encouraging since the complex responded reversibly to CO.

Using the weakly guiding and exact field solutions of an optical fiber, we wrote a FORTRAN program to determine the fractional power that reaches the end of an optical fiber with an absorptive cladding. We have assumed that each mode of the fiber is equally excited. This corresponds to incoherent source excitation. The results were compared to a previous approximations published in the literature. We have found that, at low V-numbers, V < 20, Payne and Hale's approximation deviate by more than 20% from the weakly guiding solution. At high V-numbers, the approximation deviated by less than 10%. When compared to Payne and Hale's approximation, both the weakly guiding and exact solutions are closer to the data points obtained experimentally by Degrandpre and Burgess. Although closer than Payne and Hale's approximation, our solution still deviates from Degrandpre and Burgess' results. The difference may be due to the assumption that all modes were excited equally. Another possibility was the fact that we have neglected leaky modes in our treatment.

We present a new fiber-optic oxygen microsensor based on dynamic luminescence quenching which was recently developed for measuring oxygen at high spatial resolution in aquatic sediments and biofilms. Micro-optrodes with a typical tip diameter of 20 to 50 micrometers were fabricated. The fabrication procedure is simple and guarantees a high reproducibility of the calibration curves. The micro-optrodes were characterized with respect to dynamic range, response time, storage, longterm stability, interferences, temperature dependence, photostability, and mechanical stability. A special LED based luminescence intensity measuring instrument was developed. It is battery operated and can be used for field measurements. The micro-optrodes were used to measure oxygen gradients in marine sediments. Comparative measurements were performed with oxgen microelectrodes. The first measurements have shown that oxygen micro-optrodes present a true alternative to existing electrochemical microsensors. Nevertheless, it is obvious, that the measurement of luminescence intensity of the indicator limits their practical application. Therefore a new setup was developed to make oxygen measurements with the luminescence lifetime as parameter.

New fiber optic oxygen microsensors (microoptrodes) for use in aquatic environments have recently been developed as an alternative to commonly used CLark-type oxygen microelectrodes. The microoptrodes have the advantage of no oxygen consumption and no stirring sensitivity combined with a simple manufacturing process of the sensors. To avoid problems inherent to luminescence intensity measurements like photobleaching, signal dependency on the optical properties of the surrounding medium and system drifts, a novel measuring system was developed. This system uses a phase modulation method to evaluate a signal phase shift that is caused by the oxygen dependent luminescence lifetime. The measuring system is based on simple solid state technology. High reliability and low costs of the system can therefore be combined with the ability of miniaturization and low power consumption. The system consists of three units: 1) the microoptrode with the optical setup [glass fiber coupler, optical filters, lenses, light source (light emitting diode) and light detection (photon multiplier tube)], 2) the analogue signal processing unit, including a special phase detection module, and 3) the digital signal processing unit, a personal computer or a microcontroller for control of the measuring system, display and data storage. First measurements of oxygen depth profiles in sediments and biofilms at high levels of ambient light demonstrated the advantages of phase shift based O₂ measurements as compared to intensity based measurements with microoptrodes.

The TeX glasses are attracting much attention as materials for low loss mid-IR optical fibers and are consequently good candidates for thermal imaging, laser power delivery, and more recently remote sensing. The TeX glass fiber, transmitting in a wide optical window, has a minimum attenuation in the 9-10 micrometers region. Fibers with an attenuation of less than 0.5 dB/m have been repeatly obtained. These fibers are coated with a UV curable or thermal plastic, in order to improve their mechanical properites. The IR remote spectroscopy using TeX fibers is one of the most promising applications. This technology allows to perform in situ, real-time, and on-line analysis of chemical and biological compounds. The study of industrial processes such as fermentations has been performed by this method, based on the use of these IR TeX fibers.