1,720,969 research outputs found
Opto-electronic systems for addressing Ru oxygen sensors: their design optimization and calibration process
No full textThe paper describes research at Southampton University, aimed at optimising the design of fibre-remoted dissolved-oxygen sensors, using immobilized fluorescent Ru2+ indicators. The design and construction of two types of fluorescence lifetime monitoring units, one type using phase-delay-monitoring and the other using photon counting, is described. Results from a detailed theoretical study of a photon-counting RLD fluorescence lifetime sensor are presented, with specific attention to noise aspects. By numerical modeling of an analytical solution, the optimum time-window boundaries for the photon-counting system are identified. A surprising result is that the signal/noise can actually be improved by not using photon counts from all of the exponential decay, but leaving a time-gap in the measurement improves lifetime accuracy. Our previously reported Ti3+-doped sapphire fluorescence-lifetime calibration probe is described, and a new method for RLD interrogator verification using the probe is demonstrated.<br/
Simultaneous sensing of dissolved oxygen and probe temperature using a ruby insert and compact photon counting receiver
No full textWe present a new sensor capable of real-time simultaneous determination of dissolved oxygen and temperature sensor. The measurements are achieved by essentially simultaneous interrogation of fluorescence lifetime of both an oxygen sensing Ru2+ pO2 sensor membrane impregnated in silicone, and a Cr3+-doped sapphire crystal (Ruby). The presence of the ruby crystal provides several advantages 1. It acts as a thermal sensor at the probe tip, that is illuminated by the same LED as the Ru2+ sensing layer. 2. As the ruby crystal is mounted at the distal end of the optical fibre probe, it provides a reference signal to indicate mechanical damage or membrane detachment problems. 3. By providing a reasonably constant fluorescence intensity, more significant, yet gradual changes in fluorescence light output from the membrane (e.g. due to photo-degradation) may be detected
Model to predict the response of correlation spectroscopy gas detection systems for CH<sub>4</sub>
No full textWe present a comprehensive model of a correlation spectroscopy gas sensor for CH4. Response and performance are predicted for typical fibre optic-coupled systems
Design of a photon-counting interrogation unit for monitoring Ru<sup>2+</sup> oxygen sensors
No full textBy combining recently available photomultiplier-based photon-counting modules with simple optics and electronics, it is possible to construct highly sensitive, yet reasonably compact, fluorescence lifetime monitors, capable of working with extremely low fluorescent-light return levels. Measurements are rapid, the unit operates with relatively little excitation cross-talk (due to temporal separation of send and return signals) and the same basic apparatus can be used as a diagnostic tool to characterise the fluorescent decay curves from layers. The presented sensor, which is designed to interrogate Ru2+ complex indicator dyes (fluorescence lifetime in the range 3-7 microseconds), derives excitation light from an HP high-intensity blue LED source (a flash-lamp is not required). With the aid of a dichroic splitter block, a single optical fibre is used to guide excitation light to the dye and to collect the resulting fluorescence
Model to predict the response of a correlation spectroscopy system for the detection of oxygen gas
No full textWe present the first comprehensive model for the detection of a gas by absorption based correlation spectroscopy, and show the practically useful results obtained. Predictions of sensor response for a fibre-optic-coupled O detection limits have been derived
Use of transition-metal-doped sapphire crystals to calibrate and thermally compensate fluorescent-lifetime chemical detectors
No full textThe paper describes the first use of a plug-in Ti3+- doped sapphire probe to act as a fluorescence-lifetime calibration aid. It has been used for validating a blue-LED-based optoelectronic system designed to interrogate a Ru2+ dye oxygen sensor. Ti-sapphire has a compatible absorption and fluorescence spectrum and a similar fluorescence lifetime to Ru2+ dye, and its lifetime can be varied, in a predictable manner, by heating or cooling. Use of a small Cr3+- doped sapphire crystal (ruby), close to the Ru2+ dye indicator at the probe tip, is also proposed as a temperature monitor, and has, for the first time, been interrogated using the same light source, detector and phase-delay electronics as the Ru2+ dye chemical probe
High performance architecture design for large scale fibre-optic sensor arrays using distributed EDFAs and hybrid TDM/DWDM
Full text linkA distributed amplified dense wavelength division multiplexing (DWDM) array architecture is presented for interferometric fibre optic sensor array systems. This architecture employs a distributed erbium doped fibre amplifier (EDFA) scheme to decrease the array insertion loss, and employs time division multiplexing (TDM) at each wavelength to increase the number of sensors that can be supported. The first experimental demonstration of this system is reported including results which show the potential for multiplexing and interrogating up to 4096 sensors using a single telemetry fibre pair with good system performance. The number can be increased to 8192 by using dual pump sources
Full characterization and comparison of phase properties of narrow linewidth lasers operating in the C-band
No full textWe characterize and compare the performance of various commercially available lasers in terms of their absolute frequency stability, lineshape and linewidth, and frequency noise. The frequency stability, linewidth and lineshape are evaluated using an ‘optical ruler’ - a carrier-envelope stabilized optical comb. The frequency noise is measured over an extended spectral range starting from 2 Hz. The performed analysis gives data necessary when deciding which laser to use in a particular application
Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system
No full textSummary: This paper presents recent measurements of novel Eu3+-complex doped sol gel layers (ref 1) which are intended for use as pH indicators, with interrogation by monitoring their fluorescent decay with a compact photon-counting receiver (ref 2). The basic chemistry is outlined and the instrumental arrangement and experimental results are described.Requirements and basic concept of indicator chemistry. Luminescent lanthanide chelates have many applications, being useful alternatives to standard fluorescent dyes especially when there is significant autofluorescence. They are also useful donors for use in energy transfer experiments to determine static inter-molecular distances. These applications arise because of the chelates' excellent solubility and unusual spectral characteristics, including narrow (<10 nm) spectral emission, large Stokes shifts (>150 nm), potentially high quantum yields. Selvin et al. have synthesized several lanthanide chelates but all show inconvenient excitation maxima around 340 nm. In contrast, our novel long-wave luminescent dye, based on europium luminescence initiated by a covalently-bonded antenna fluorophor, shows excitation maxima at 370 nm where low cost LEDs are now available. To design sensors of high stability and long lifetime, the sensor matrix and sensor technology are of prime interest. Sol-gel technology enables the production of proton-permeable glassy layers at room temperature and offers simple methods for manipulation of the basic composition, molecular structure, and hence the chemical characteristics of organic matrices. Time-resolved fluorometry is preferable to conventional fluorometry, since there are no intensity related problems due to turbid samples, self-filter effect, and cuvette geometry. Also, the fluorescence decay time is usually independent of the concentration of the indicator, even when it has been partially modified by leaching out, by decomposition, or by photo bleaching. In the current work, the Eu3+-complex has been successfully entrapped into tetramethoxysilane (TMOS)-based sol-gel matrices. It was initially found that a Eu3+-complex, which showed useful pH sensitivity in aqueous solution, lost this sensitivity when immobilized in sol-gel matrices. In order to recover this property, the pH indicator bromothymol blue (BTB) was added to the starting sol-gel components and it was found that the useful pH response that was present in water was not only restored, but was actually improved upon. Instrumentation and experiment for interrogation of Eu3+-complex-doped sol-gel coated layer. The arrangement shown in fig 1 was used for rapid interrogation of fluorescence lifetime. The arrangement improves signal to noise because the sol-gel coating is illuminated directly with a filtered UV LED source, rather than via an optical fibre probe. This increases illumination intensity by removing optical power loss in the launch optics, illuminates a large coating area, and reduces the background auto-fluorescence signal generated from combined launch and return optics. The main excitation peak occurs at 370 nm, which falls in the absorption band of the pH-sensing layer. It should be noted that this arrangement, which was used to improve signal to noise and reduce self-fluorescence in our measurement, was considered to be only an interim step on the way to developing an all-fibre system for illumination and collection of light. Clearly similar gains in signal can be achieved by using larger input and output fibres or fibre bundles, and self-fluorescence can be reduced by use of separate fibre cables for incident and fluorescent light.<br/
Fibre optic LED-based correlation spectroscopy for O<sub>2</sub> detection
No full textThis paper describes the first detection of O2 by Complementary-Source-Modulation (CoSM) correlation spectroscopy over optical fibre with compact LED sources. Theoretical results for the selective detection of O2 by the CoSM method are also presented, based on spectral absorption data from the Hitran database
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