Novel miniature spectrometer for remote chemical detection. 1998 annual progress report (original) (raw)
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Cavity ring down spectroscopy: detection of trace amounts of substance
We describe several applications of cavity ring−down spectroscopy (CRDS) for trace matter detection. NO 2 sensor was con− structed in our team using this technique and blue−violet lasers (395–440 nm). Its sensitivity is better than single ppb. CRDS at 627 nm was used for detection of NO 3. Successful monitoring of N 2 O in air requires high precision mid−infrared spectros− copy. These sensors might be used for atmospheric purity monitoring as well as for explosives detection. Here, the spectros− copy on sharp vibronic molecular resonances is performed. Therefore the single mode lasers which can be tuned to selected molecular lines are used. Similarly, the spectroscopy at 936 nm was used for sensitive water vapour detection. The opportu− nity of construction of H 2 O sensor reaching the sensitivity about 10 ppb is also discussed.
Near-surface reduction of cavity ring-down spectroscopy detection sensitivity
Chemical Physics Letters, 2000
. Cavity ring-down spectroscopy CRDS is a high-sensitivity technique used to measure the absolute concentrations of absorbing species. We have used CRDS to measure spatially dependent concentration profiles near a physical surface that obstructs the light path. A decrease in detection sensitivity resulting from interaction between the circulating cavity ring-down beam and the surface was observed. Simple calculations based on geometrical obstruction by the solid surface significantly underestimate the sensitivity loss, suggesting that diffraction is important. Calculations that include diffraction effects more closely agree with experimental data. q
A chemical sensor for alternative barriers using NIR spectroscopy
Environmental Geotechnics, 2016
Remediation of contaminated sites often includes the use of alternative barriers as a passive treatment method for a variety of contaminants and sites. Alternative barriers, in turn, require a means for monitoring their performance directly, without the need for costly sampling. It is ideal that the monitoring system provide the data in real time and remotely. When combined with optical fibres, near-infrared (NIR) spectroscopy is a promising chemical sensor for in situ, on-site detection of contaminants. This technology has important advantages over other sensors: it can be used to identify hydrocarbonscapable of distinguishing between chemical groups such as alkanes and chlorinated, aromatic and polyaromatic hydrocarbons, as well as distinguishing compounds within the same homologous series of hydrocarbons. Furthermore, with the combined use of lipophilic polymer coatings and tip sensors, the waveguide can be turned into a localised chemical sensor. Coupled with the fact that the new generation of spectrometers are lower in cost and smaller in size than their predecessors, such a sensor can be installed in the field where communications technologies can transmit data from a remote locationideally suited for alternative barriers as a means of monitoring the subsurface environment and the performance of the barrier.
Single-cell detection by cavity ring-down spectroscopy
Applied Physics Letters, 2004
The implementation of cavity ring-down spectroscopy in an optical fiber resonator extends the viability of this highly sensitive technique for label-free detection of biological species. By chemically treating the surface of discrete tapered sensing regions along the length of a physically extended optical fiber resonator, we show single-cell sensitivity arising from optical scattering of the evanescent field surrounding the fiber. The observed detection limits, based on a minimum detectable scattering cross section on the order of 10 m 2 , suggest a broad range of new applications in a simple, inexpensive device for real-time cavity ring-down biosensing.
Chemical and biochemical sensors based on interferometry at thin (multi-) layers
Sensors and Actuators B: Chemical, 1993
Spectral interferometry is presented as a tool to monitor the swelling of polymers caused by organic gases or hydrocarbons in waste water as well as the adsorption and interaction of antigens and antibodies in immunoreactions. Modem diode-array technology allows the consequent observation of changes in optical pathlength on a fractional nanometer scale with subsecond repetition times. The theory of multiple-reflection principles in white-li&t interferometry determines the possibilities and limitations of this method. The optical set-up and some applications in gas sensing and label-free immunosensing are discussed with respect to the sensitivity, selectivity and limits of detection at present.
Recent developments in optical transducers for chemical or biochemical applications
Sensors and Actuators B Chemical, 1997
A variety of optical transducers is presented in the literature based on just a few given optical principles. Based on principles like microrefractometry and -reflectivity, a classification is approached, especially for sensors used in bioanalytics. Two methods are discussed in detail, which are favoured in the group known as integrated optical Mach-Zehnder interferometers and reflectometric interference spectroscopy (RIfS) . Recent applications as chemical sensors and biochemical probes in the fields of hydrocarbon monitoring and immunoreactions are demonstrated. Perspectives in routine interaction analysis, microstructuring of devices, direct detection of low-molecular-weight ligands, and parallel high-throughput screening are discussed. . ' Plenary lecture. 0925-4005/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved Prrs0925-4005(97)00042-7 2 A. Brecht, G. Gauglitz/Sensors
Integrated optical technologies for analytical sensing
2004
Recent diversification of the telecommunications industry has resulted in the adaptation of optical materials and their associated fabrication technologies for use in the bioanalytical sensor industry. Flame hydrolysis deposited (FHD) planar silica is one such material. Capable of producing high quality films for optical waveguides, the chemical inertness of the deposited silica makes it an ideal substrate from which to fabricate a biological fluorescence sensor. The aim of the work contained in this thesis was to utilise the FHD silica in optical - fluorescence sensors suitable for use at visible and in particular red wavelengths where several fluorophores can be excited, and background fluorescence from the silica is small. New technologies for producing waveguides have been evaluated in the context of their usefulness in optical sensors, with the intention of producing devices with as few fabrication steps as possible to reduce fabrication time and cost. The design, fabrication a...
Origins of Life and Evolution of Biospheres, 2006
Absorption or emission spectroscopy is a powerful tool for detecting chemical compounds, diluted in fluid media: the sensitivity of this technique depends on the optical path of the source radiation, on the spectral window used for analysis and on the spectrometer performances. In this view, we designed and produced the first prototypes of an integrated scanning Fourier Transform Microinterferometer with Mach-Zehnder geometry, by using MEOS (Micro Electro Optical Systems) technologies. The microdevice, obtained by fabricating integrated optical waveguides on LiNbO 3 (LN) crystals, is electrically driven, without moving parts, by exploiting the electrooptical properties of the material. The microdevice operates the Fourier Transform of the input radiation spectral distribution, which can be reconstructed starting from the output signal by means of Fast Fourier Transform (FFT) techniques. The microinterferometer weights few grams, the power consumption is of a few mW and, in principle, can operate in the LN transmittance range (0.36-4.5 μm). The microinterferometer performances were preliminary tested in the (0.4-1.7 μm) spectral window. In the Visible region (0.4-0.7 μm) this microsystem demonstrated a spectral resolution suitable for detecting the characteristic lines of the solar spectrum together with the absorption bands of common gases present in Earth's atmosphere. In a further experiment we tested its performances for gas trace detection by using a calibrated NO 2 optical gas cell, showing the possibility to reveal up to 10 ppb, when suitable optical paths are used. Finally, colorimetry tests for the titration of an organic dye (E131) in alcohol solution are presented.
Recent Progress in Optical Chemical Sensors
Sensors, 2012
Optical chemical sensors have promoted escalating interest in the determination of various pollutants in the environment, which are creating toxicity and may cause serious health problems. This review paper focuses particularly on the recent progress and developments in this field; the working principles and basic classes of optical chemical sensors have been briefly described.