Dr. George Stewart Profile

Dr. George Stewart

Reader at Univ of Strathclyde

SPIE Involvement:

Author

Publications (42)

Proceedings Article | 17 May 2011 Paper

Fibre lasers for photo-acoustic gas spectroscopy

Norhana Arsad, George Stewart

Proceedings Volume 7753, 77533L (2011) https://doi.org/10.1117/12.884944

KEYWORDS: Modulation, Fiber lasers, Absorption, Spectroscopy, Fiber Bragg gratings, Acoustics, Optical amplifiers, Amplitude modulation, Semiconductor lasers, Phase modulation

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Proceedings Article | 14 May 2010 Paper

Recovery of acetylene absorption line profile basing on tunable diode laser spectroscopy with intensity modulation and photoacoustic spectroscopy

Li Li, Graham Thursby, George Stewart, Norhana Arsad, Deepak Uttamchandani, Brian Culshaw, Yiding Wang

Proceedings Volume 7726, 77261O (2010) https://doi.org/10.1117/12.854075

KEYWORDS: Absorption, Modulation, Photoacoustic spectroscopy, Mirrors, Microelectromechanical systems, Actuators, Spectroscopy, Signal detection, Laser spectroscopy, Tunable diode lasers

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A novel and direct absorption line recovery technique based on tunable diode laser spectroscopy with intensity modulation is presented. Photoacoustic spectroscopy is applied for high sensitivity, zero background and efficient acoustic enhancement at a low modulation frequency. A micro-electromechanical systems (MEMS) mirror driven by an electrothermal actuator is used for generating laser intensity modulation (without wavelength modulation) through the external reflection. The MEMS mirror with 10μm thick structure material layer and 100nm thick gold coating is formed as a circular mirror of 2mm diameter attached to an electrothermal actuator and is fabricated on a chip that is wire-bonded and placed on a PCB holder. Low modulation frequency is adopted (since the resonant frequencies of the photoacoustic gas cell and the electrothermal actuator are different) and intrinsic high signal amplitude characteristics in low frequency region achieved from measured frequency responses for the MEMS mirror and the gas cell. Based on the property of photoacoustic spectroscopy and Beer's law that detectable sensitivity is a function of input laser intensity in the case of constant gas concentration and laser path length, a Keopsys erbium doped fibre amplifier (EDFA) with opto-communication C band and high output power up to 1W is chosen to increase the laser power. High modulation depth is achieved through adjusting the MEMS mirror's reflection position and driving voltage. In order to scan through the target gas absorption line, the temperature swept method is adopted for the tunable distributed feed-back (DFB) diode laser working at 1535nm that accesses the near-infrared vibration-rotation spectrum of acetylene. The profile of acetylene P17 absorption line at 1535.39nm is recovered ideally for ~100 parts-per-million (ppm) acetylene balanced by nitrogen. The experimental signal to noise ratio (SNR) of absorption line recovery for 500mW laser power was ~80 and hence the detectable sensitivity is of the order of 1ppm.

Proceedings Article | 20 April 2010 Paper

Near infrared spectroscopy for fibre based gas detection

George Stewart, Walter Johnstone, Graham Thursby, Brian Culshaw

Proceedings Volume 7675, 767507 (2010) https://doi.org/10.1117/12.852919

KEYWORDS: Modulation, Absorption, Methane, Sensing systems, Gases, Calibration, Tunable diode lasers, Phase shift keying, Sensors, Fiber optics

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Proceedings Article | 5 October 2009 Paper

Recent advance in tunable diode laser spectroscopy with background RAM nulling for industrial applications

Keith Ruxton, Arup Lal Chakraborty, Andrew McGettrick, Kevin Duffin, Walter Johnstone, George Stewart

Proceedings Volume 7503, 750313 (2009) https://doi.org/10.1117/12.833000

KEYWORDS: Absorption, Modulation, Spectroscopy, Nulling interferometry, Lenses, Tunable diode lasers, Laser spectroscopy, Near infrared, Resonators, Phase shift keying

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Proceedings Article | 5 October 2009 Paper

Intra-cavity spectroscopy using amplified spontaneous emission in erbium fibre lasers

Norhana Arsad, George Stewart

Proceedings Volume 7503, 750312 (2009) https://doi.org/10.1117/12.834330

KEYWORDS: Fiber lasers, Absorption, Erbium, Gas sensors, Gases, Micro optics, Laser spectroscopy, Spectroscopy, Signal attenuation, Laser systems engineering

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Proceedings Article | 5 October 2009 Paper

Direct monitoring of underwater ultrasonic transducers in the near field using fibre Bragg grating sensors

G. M. Flockhart, M. McGuire, S. Pierce, G. Thursby, G. Stewart, G. Hayward, B. Culshaw

Proceedings Volume 7503, 750331 (2009) https://doi.org/10.1117/12.835468

KEYWORDS: Fiber Bragg gratings, Transducers, Sensors, Ultrasonics, Acoustics, Optical fibers, Near field, Ferroelectric polymers, Optical amplifiers, Wave propagation

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Proceedings Article | 19 February 2009 Paper

Stable, tunable, and single-mode operation of an erbium-doped fibre laser system using a saturable absorber for gas spectroscopy applications

Norhana Arsad, George Stewart

Proceedings Volume 7195, 719525 (2009) https://doi.org/10.1117/12.808157

KEYWORDS: Signal attenuation, Fiber lasers, Modulation, Fiber Bragg gratings, Absorption, Ferroelectric materials, Laser systems engineering, Spectroscopy, Optical amplifiers, Amplitude modulation

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Proceedings Article | 28 April 2008 Paper

Tunable diode and fibre laser spectroscopy in the near-IR for measurement of gas parameters

George Stewart, Walter Johnstone, Norhana Arsad, Kevin Duffin

Proceedings Volume 7003, 700319 (2008) https://doi.org/10.1117/12.779976

KEYWORDS: Modulation, Fiber lasers, Absorption, Semiconductor lasers, Spectroscopy, Amplitude modulation, Laser spectroscopy, Phase shift keying, Calibration, Frequency modulation

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Proceedings Article | 25 September 2007 Paper

An alternative approach to wavelength modulation spectroscopy for absolute measurements of gas parameters in industrial processes

Walter Johnstone, Kevin Duffin, Andrew McGettrick, George Stewart

Proceedings Volume 6756, 675602 (2007) https://doi.org/10.1117/12.731769

KEYWORDS: Modulation, Absorption, Frequency modulation, Signal detection, Amplitude modulation, Fermium, Calibration, Spectroscopy, Phase shift keying, Chlorine

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Proceedings Article | 2 July 2007 Paper

Tunable diode laser spectroscopy for industrial process applications

Kevin Duffin, Andrew McGettrick, Walter Johnstone, George Stewart

Proceedings Volume 6619, 661927 (2007) https://doi.org/10.1117/12.738641

KEYWORDS: Modulation, Absorption, Frequency modulation, Amplitude modulation, Fermium, Spectroscopy, Tunable diode lasers, Laser spectroscopy, Signal detection, Calibration

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Proceedings Article | 2 July 2007 Paper

Design of a multi-wavelength fibre laser using an intra-cavity phase modulator and Sagnac loop filter for sensor applications

M. Mirza, G. Stewart

Proceedings Volume 6619, 66192K (2007) https://doi.org/10.1117/12.738637

KEYWORDS: Optical amplifiers, Modulation, Modulators, Sensors, Fiber lasers, Optical filters, Ferroelectric materials, Phase shift keying, Polarization, Fiber Bragg gratings

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Proceedings Article | 20 October 2006 Paper

Analysis of the transient response of erbium fibre lasers and application for sensors

George Stewart, Gillian Whitenett, Brian Culshaw

Proceedings Volume 6371, 63710N (2006) https://doi.org/10.1117/12.684669

KEYWORDS: Sensors, Absorption, Fiber lasers, Erbium, Chemical elements, Signal attenuation, Spectroscopy, Chemical analysis, Erbium lasers, Pulsed laser operation

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Proceedings Article | 24 September 2005 Paper

Tunable diode laser spectroscopy over optical fibres for gas measurements in harsh industrial environments

Walter Johnstone, Kevin Duffin, Andrew McGettrick, George Stewart, Amy Cheung, D. Moodie

Proceedings Volume 5952, 595206 (2005) https://doi.org/10.1117/12.622820

KEYWORDS: Signal detection, Spectroscopy, Optical fibers, Absorption, Laser spectroscopy, Amplitude modulation, Frequency modulation, Tunable diode lasers, Modulation, Fermium

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Proceedings Article | 23 May 2005 Paper

Tuneable L band multi-wavelength fiber laser using silicon wafers

Joanna Marshall, George Stewart, Gillian Whitenett, Brian Culshaw

Proceedings Volume 5855, (2005) https://doi.org/10.1117/12.624385

KEYWORDS: Silicon, Semiconducting wafers, Fiber lasers, L band, Semiconductor lasers, Absorption, Micro optics, Gases, Carbon monoxide, Attenuators

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Proceedings Article | 23 May 2005 Paper

Optical fibre sensors based on the dynamic response of fibre lasers

George Stewart, V. Karthik, Gillian Whitenett

Proceedings Volume 5855, (2005) https://doi.org/10.1117/12.624387

KEYWORDS: Sensors, Fiber lasers, Erbium, Optical fibers, Optical simulations, Chemical elements, Erbium lasers, Absorption, Stereolithography, Laser resonators

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Proceedings Article | 14 December 2004 Paper

Development of a 32-element fiber optic hydrophone system

Zhou Meng, Yongming Hu, Ming Ni, Shuidong Xiong, Renhe Zhang, Xiuling Li, George Stewart, FengZhong Dong, Brian Culshaw

Proceedings Volume 5589, (2004) https://doi.org/10.1117/12.577842

KEYWORDS: Signal detection, Fiber optics, Optical components, Acoustics, Fiber optic components, Protactinium, Polarization, Ocean optics, Optical fibers, Digital signal processing

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Proceedings Article | 1 September 2004 Paper

Remote gas analysis using fibre optic links and near infrared absorption

George Stewart, Gillian Whitenett, Joanna Marshall, Walter Johnstone, Brian Culshaw, Alistair MacLean, Iain Mauchline, David Moodie

Proceedings Volume 5459, (2004) https://doi.org/10.1117/12.555345

KEYWORDS: Surface plasmons, Absorption, Methane, Near infrared, Fiber optics, Spectroscopy, Optical fibers, Gases, Modulation, Hydrogen

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Proceedings Article | 9 June 2004 Paper

Fibre lasers for near-IR gas spectroscopy

George Stewart, Gillian Whitenett, Joanna Marshall, Brian Culshaw

Proceedings Volume 5502, (2004) https://doi.org/10.1117/12.566794

KEYWORDS: Fiber lasers, Spectroscopy, Polarization, Gas sensors, Fiber amplifiers, Sensors, Mode locking, Modulators, Absorption, Gas lasers

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Proceedings Article | 8 March 2004 Paper

Design of fiber laser and sensor systems for gas spectroscopy in the near-IR

George Stewart, Gillian Whitenett, Peter Shields, Joanna Marshall, Brian Culshaw

Proceedings Volume 5272, (2004) https://doi.org/10.1117/12.515651

KEYWORDS: Sensors, Fiber lasers, Laser systems engineering, Spectroscopy, Laser development, Near infrared spectroscopy, Telecommunications, Fiber optics, Gases, Gas sensors

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Proceedings Article | 19 November 2003 Paper

Optical fibre sensors for environmental monitoring of trace gases

George Stewart, Gillian Whitenett, Kathryn Atherton, Brian Culshaw, Walter Johnstone

Proceedings Volume 4829, (2003) https://doi.org/10.1117/12.527028

KEYWORDS: Gases, Sensors, Methane, Fiber lasers, Spectroscopy, Fiber optics sensors, Laser sources, Gas sensors, Optical fibers, Environmental monitoring

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Proceedings Article | 22 February 2002 Paper

Gas detection by cavity ringdown absorption with a fiber optic amplifier loop

Kathryn Atherton, George Stewart, Brian Culshaw

Proceedings Volume 4577, (2002) https://doi.org/10.1117/12.455741

KEYWORDS: Optical amplifiers, Fiber amplifiers, Signal attenuation, Erbium, Optical fibers, Absorption, Micro optics, Gas sensors, Optical gas detection, Fiber optics

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Proceedings Article | 1 March 2001 Paper

Fiber optic intra-cavity spectroscopy: combined ring-down and ICLAS architectures using fiber lasers

Kathryn Atherton, George Stewart, H. Yu, Brian Culshaw

Proceedings Volume 4204, (2001) https://doi.org/10.1117/12.417401

KEYWORDS: Absorption, Signal attenuation, Erbium, Fiber amplifiers, Optical fibers, Micro optics, Optical amplifiers, Spectroscopy, Fiber lasers, Fiber optics

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Proceedings Article | 9 November 2000 Paper

Intra-cavity and ring-down cavity absorption with fibre amplifiers for trace gas detection

George Stewart

Proceedings Volume 4185, 41852F (2000) https://doi.org/10.1117/12.2302230

KEYWORDS: Absorption, Micro optics, Modulation, Fiber amplifiers, Fiber lasers, Fiber optics, Absorbance, Laser systems engineering, Gases, Methane

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SPIE Journal Paper | 1 November 2000

Analysis of quasi-distributed optical sensors combining RF modulation with the FMCW method

Miha Zavrsnik, George Stewart

OE, Vol. 39, Issue 11, (November 2000) https://doi.org/10.1117/12.10.1117/1.1315025

KEYWORDS: Modulation, Absorption, Frequency modulation, Fermium, Absorbance, Optical sensors, Sensors, Semiconductor lasers, Methane, Micro optics

Proceedings Article | 31 August 2000 Paper

Field evaluation of a multipoint fiber optic sensor array for methane detection (OMEGA)

Jane Hodgkinson, Russell Pride, Chris Tandy, David Moodie, George Stewart

Proceedings Volume 4074, (2000) https://doi.org/10.1117/12.397868

KEYWORDS: Sensors, Calibration, Methane, Head, Gas sensors, Optical sensors, Gases, Absorption, Fiber optics sensors, Optical arrays

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Proceedings Article | 12 June 2000 Paper

Characterization and application of FMCW coherence-addressed quasi-distributed absorption sensors

Miha Zavrsnik, George Stewart

Proceedings Volume 3986, (2000) https://doi.org/10.1117/12.388125

KEYWORDS: Absorption, Sensors, Signal attenuation, GRIN lenses, Methane, Sensing systems, Micro optics, Interfaces, Semiconductor lasers, Modulation

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Proceedings Article | 31 May 1999 Paper

Coherence addressing of quasi-distributed absorption sensors by the FMCW method

Miha Zavrsnik, George Stewart

Proceedings Volume 3670, (1999) https://doi.org/10.1117/12.349741

KEYWORDS: Absorption, Sensors, GRIN lenses, Modulation, Micro optics, Capillaries, Sensing systems, Microscopes, Methane, Signal processing

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Proceedings Article | 13 August 1998 Paper

Interferometric noise in fiber optic gas sensors using wavelength modulation spectroscopy

Wei Jin, Yuanzhong Xu, M. Suleyman Demokan, George Stewart, Brian Culshaw

Proceedings Volume 3555, (1998) https://doi.org/10.1117/12.318222

KEYWORDS: Modulation, Interferometry, Gas sensors, Absorption, Fiber optics sensors, Sensors, Spectroscopy, Signal detection, Connectors, Fiber optics

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Proceedings Article | 18 June 1998 Paper

Multipoint fibre sensors for trace gas monitoring using derivative spectroscopy

George Stewart, Brian Culshaw, Chris Tandy, David Moodie, Russell Pride

Proceedings Volume 3483, (1998) https://doi.org/10.1117/12.309658

KEYWORDS: Absorption, Modulation, Sensors, Methane, Spectroscopy, Fiber optics sensors, Gases, Gas sensors, Laser sources, Fabry–Perot interferometers

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Proceedings Article | 30 May 1997 Paper

Coherent backscatter noise in fiber optic gas sensors

Wei Jin, M. Suleyman Demokan, George Stewart, Wayne Philp, Brian Culshaw

Proceedings Volume 3105, (1997) https://doi.org/10.1117/12.276161

KEYWORDS: Backscatter, Sensors, Gas sensors, Absorption, Light scattering, Fiber optics sensors, Fiber optics, Methane, Optical resolution, Photodetectors

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SPIE Journal Paper | 1 January 1997

Design of an integrated optic comb filter based on coupling between dissimilar waveguides

E. Peral, George Stewart, Iain Mauchline

OE, Vol. 36, Issue 01, (January 1997) https://doi.org/10.1117/12.10.1117/1.601131

KEYWORDS: Linear filtering, Waveguides, Integrated optics, Optical filters, Optical engineering, Information operations, Glasses, Lithium niobate, Wave propagation, Phase matching

Proceedings Article | 24 September 1996 Paper

Effect of noise in fiber optic gas sensors

Wei Jin, George Stewart, Wayne Philp, Brian Culshaw, M. Suleyman Demokan

Proceedings Volume 2895, (1996) https://doi.org/10.1117/12.252138

KEYWORDS: Reflection, Absorption, Sensors, Gas sensors, Interferometry, Fiber optics sensors, Interference (communication), Fiber optics, Sensing systems, Laser sources

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Proceedings Article | 13 October 1995 Open Access

Fiber optic communications experiments for undergraduates

Brian Culshaw, Walter Johnstone, George Stewart, Douglas Walsh

Proceedings Volume 2525, (1995) https://doi.org/10.1117/12.224050

KEYWORDS: Dispersion, Telecommunications, Waveguides, Light emitting diodes, Optical communications, Receivers, Signal attenuation, Optical fibers, Fiber optic communications, Semiconductor lasers

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Proceedings Article | 20 April 1995 Paper

Pseudo-depolarizer for interferometric fiber sensor applications

Wei Jin, George Stewart, Kenneth Crawford, Brian Culshaw

Proceedings Volume 2574, (1995) https://doi.org/10.1117/12.207757

KEYWORDS: Modulation, Birefringence, Polarization, Modulators, Sensors, Polarizers, Fiber optics sensors, Interferometry, Light, Linear filtering

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Proceedings Article | 21 October 1994 Paper

Performance limitation of a D-fiber evanescent wave methane sensor due to interference effects

Wei Jin, George Stewart, Brian Culshaw, Stuart Murray, Mark Wilkinson, John Norris

Proceedings Volume 2293, (1994) https://doi.org/10.1117/12.190972

KEYWORDS: Methane, Polarization, Sensors, Birefringence, Fabry–Perot interferometers, Modulation, Wave sensors, Sensing systems, Signal attenuation, Fabry–Perot interferometry

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Proceedings Article | 14 September 1994 Paper

Source noise limitation of fibre optic methane sensors

Wei Jin, George Stewart, Brian Culshaw, Stuart Murray

Proceedings Volume 2360, (1994) https://doi.org/10.1117/12.185008

KEYWORDS: Methane, Sensors, Light, Absorption, Reflectivity, Fiber optics, Modulation, Optical filters, Fabry–Perot interferometers, Light emitting diodes

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Proceedings Article | 14 September 1994 Paper

Monitoring of surface contamination in an evanescent-wave gas sensor using white light interferometry

Wei Jin, George Stewart, Brian Culshaw

Proceedings Volume 2360, (1994) https://doi.org/10.1117/12.184959

KEYWORDS: Contamination, Birefringence, Michelson interferometers, Optical interferometry, Polarization, Water, Interferometers, Gas sensors, Methane, Sensors

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Proceedings Article | 10 March 1994 Paper

Parameter optimization in a methane detection system using a broadband source and interferometric signal processing

Wei Jin, George Stewart, Brian Culshaw, Stuart Murray, David Pinchbeck

Proceedings Volume 2068, (1994) https://doi.org/10.1117/12.170655

KEYWORDS: Methane, Absorption, Modulation, Fabry–Perot interferometry, Fabry–Perot interferometers, Interferometry, Signal processing, Light, Mirrors, Reflectivity

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Proceedings Article | 6 April 1993 Paper

Glass integrated optic wavelength filter utilizing an ion-exchange waveguide/multimode overlay structure

Iain Mauchline, George Stewart

Proceedings Volume 1794, (1993) https://doi.org/10.1117/12.141902

KEYWORDS: Waveguides, Optical filters, Overlay metrology, Glasses, Integrated optics, Filtering (signal processing), Dispersion, Linear filtering, Zinc, Ion exchange

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Proceedings Article | 1 August 1991 Paper

Multimode approach to optical fiber components and sensors

Walter Johnstone, Graham Thursby, Brian Culshaw, S. Murray, M. Gill, Alaster McDonach, David Moodie, G. Fawcett, George Stewart, Kevin McCallion

Proceedings Volume 1506, (1991) https://doi.org/10.1117/12.45969

KEYWORDS: Sensors, Lithium niobate, Polishing, Modulators, Overlay metrology, Structured optical fibers, Electrodes, Optical fibers, Micro optics, Refractive index

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Proceedings Article | 1 March 1991 Paper

Improvement in the performance of evanescent wave chemical sensors by special waveguide structures

George Stewart, Brian Culshaw, Douglas Clark, Ivan Andonovic

Proceedings Volume 1368, (1991) https://doi.org/10.1117/12.24793

KEYWORDS: Waveguides, Wave sensors, Chemical fiber sensors, Absorption, Sensors, Contamination, Signal attenuation, Waveguide sensors, Polarization, Methane

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Proceedings Article | 1 September 1990 Paper

Referencing systems for evanescent wave sensors

George Stewart, Douglas Clark, Brian Culshaw, Ivan Andonovic

Proceedings Volume 1314, (1990) https://doi.org/10.1117/12.21987

KEYWORDS: Waveguides, Contamination, Chemical species, Signal attenuation, Polarization, Chemical fiber sensors, Sensors, Wave propagation, Wave sensors, Absorption

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Showing 5 of 42 publications

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