CERES :: Browsing by Author "Francis, Daniel"

Browsing by Author "Francis, Daniel"

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Open Access
A long-wave infra-red pulsed external-cavity QCL spectrometer using a hollow waveguide gas cell: Data
(Cranfield University, 2024-04-25 08:45) Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph
A spectrometer built using an external cavity pulsed quantum cascade laser is described. The spectrometer has a tuning range from 10 €“ 13 um (1,000 €“ 769 cm-1) and is designed to target volatile organic compounds (VOCs) which often exhibit water-free molecular absorption within the region. The spectrometer utilizes a hollow silica waveguide gas cell which has an internal volume of a few millilitres, a fast response time (~1 s), and is advantageous when only low sample volumes, similar to the cell volume, are available.
Open Access
Applied Optics: HSW gas cells for mid-IR spectroscopy (2016)
(Cranfield University, 2016-08-22 13:32) Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph
Data associated with Applied Optics submission, 'Low volume, fast response-time hollow silica waveguide gas cells for mid-IR spectroscopy'
Open Access
Compact methane sensor using an integrating sphere and interband cascade laser at 3313 nm
(Elsevier, 2023-04-23) Davis, Nicholas M.; Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph P.
We present a sensor for gas detection utilising an integrating sphere and interband cascade laser for tunable diode laser absorption spectroscopy (TDLAS). Measurements were made of the methane absorption line at 3313 nm using an integrating sphere with an effective pathlength of 70.1 cm. Gas concentrations were estimated from normalised absorption spectra with line fitting to 7 absorption lines within the scan. Testing showed that measurements were linear for methane in synthetic air for concentrations in the range 0-50ppm. With an averaging time of 20 seconds, the noise-equivalent methane concentration was 180ppb (1σ). The system requires minimal alignment, with preliminary measurements indicating the system is insensitive to vibration and misalignment of the laser input. The lack of alignment optics also allows it to be compact (190x170x120mm) and robust.
Unknown
Data supporting the publication 'Compact methane sensor using an integrating sphere and Interband Cascade Laser at 3313nm'
(Cranfield University, 2023-04-28 16:45) Davis, Nicholas; Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph
Data associated with Sensors and Actuators B submission "Compact methane sensor using an integrating sphere and Interband Cascade Laser at 3313nm"
Open Access
Data: Low-coherence and broadband confocal refractometry: Reducing the measurement time
(Cranfield University, 2023-08-31 15:39) Francis, Daniel; Hallam, Jonathan; Tatam, Ralph
Data from the paper 'Low-coherence and broadband confocal refractometry: Reducing the measurement time'
Open Access
Frequency-division multiplexing for multicomponent shearography
(Osa Optical Society of America, 2013-01-20T00:00:00Z) Bledowski, Ian A.; Charrett, Thomas O. H.; Francis, Daniel; James, Stephen W.; Tatam, Ralph P.
A new method of multiplexing the speckle patterns needed in multicomponent digital shearography systems is presented. Frequency-division multiplexing (FDM) of the measurement channels is achieved by recording speckle patterns from objects illuminated by intensity-modulated sources. Each source is modulated at a discrete frequency, which is less than half of the camera frame rate, and a bank of images of the modulated speckle patterns is captured. This allows for pixel-by-pixel Fourier-based extraction of the individual speckle patterns from peaks in the power spectra. The approach is demonstrated with a two-component in-plane shearography instrument.
Open Access
Influence of aberrations on confocal-based remote refractive index measurements
(Optical Society of America, 2019-08-13) Ford, Helen D.; Francis, Daniel; Hallam, Jonathan M.; Tatam, Ralph P.
Confocal scanning combined with low-coherence interferometry is used to provide remote refractive index and thickness measurements of transparent materials. The influence of lens aberrations in the confocal measurement is assessed through ray-trace modeling of the axial point-spread functions generated using optical configurations comprised of paired aspherics and paired achromats. Off-axis parabolic mirrors are suggested as an alternative to lenses and are shown to exhibit much more symmetric profiles provided the system numerical aperture is not too high. The modeled results compare favorably with experimental data generated using an optical instrument comprised of a broadband source and line-scan spectrometer. Refractive index and thickness measurements are made with each configuration with most mirror pairings offering better than twice the repeatability and accuracy of either lens pairing.
Open Access
Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 1: Design and implementation
(Cranfield University, 2020-05-27 20:00) Lourenco, Celia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph
Data to support manuscript Part 1.
Open Access
Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 1: Design and implementation
(Nature Publishing Group, 2020-05-26) Lourenço, Célia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph P.
A novel suite of instrumentation for the characterisation of materials held inside an air-tight tube furnace operated up to 250 °C has been developed. Real-time detection of released gases (volatile organic compounds (VOCs), CO2, NO, NO2, SO2, CO and O2) was achieved combining commercial off-the-shelf (COTS) gas sensors and sorbent tubes for further qualitative and semi-quantitative analysis by gas chromatography-mass spectrometry coupled to thermal desorption (TD-GC-MS). The test system was designed to provide a controlled flow (1000 cm3 min−1) of hydrocarbon free air through the furnace. The furnace temperature ramp was set at a rate of 5 °C min−1 with 10 min dwell points at 70 °C, 150 °C, 200 °C and 250 °C to allow time for stabilisation and further headspace sampling onto sorbent tubes. Experimental design of the instrumentation is described here and an example data set upon exposure to a gas sample is presented.
Open Access
Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite
(Nature Publishing Group, 2020-05-26) Lourenço, Cecilia; Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Staines, Stephen E.; Saffell, John R.; Walton, Christopher; Tatam, Ralph P.
We have investigated the release of gases and volatile organic compounds (VOCs) from a carbon fibre reinforced epoxy composite matrix used in aircraft structural components. Analysis was performed at several temperatures both up to and above the recommended operating temperature (121 °C) for the material, to a maximum of 250 °C. Gas chromatography-mass spectrometry (GC-MS) combined with thermal desorption (TD-GC-MS) was used to identify and quantify VOCs, and in parallel real-time gas detection with commercial off-the-shelf (COTS) gas sensors. Under hydrocarbon free air, CO, SO2, NO, NO2 and VOCs (mainly aldehydes, ketones and a carboxylic acid) were detected as the gaseous products released during the thermal exposure of the material up to 250 °C, accompanied by increased relative humidity (4%). At temperatures up to 150 °C, gas and volatile emission was limited.
Open Access
Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite
(Cranfield University, 2020-05-27 20:01) Lourenco, Celia; Francis, Daniel; Fowler, Dawn; E. Staines, Stephen; Hodgkinson, Jane; Walton, Christopher; Bergin, Sarah; Tatam, Ralph
Data to support manuscript Part 2.
Open Access
Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation
(OSA, 2016-05-10) Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph P.
We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination.
Open Access
Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation
(Cranfield University, 2016-11-28 13:52) Bergin, Sarah; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph
Data to support the following paper: Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation S Bergin, J Hodgkinson, D Francis and R P Tatam Optics Express 24 (12), 13647 - 13664, 2016 doi:10.1364/OE.24.013647
Open Access
Long-wave infrared pulsed external-cavity QCL spectrometer using a hollow waveguide gas cell
(Optica, 2024-05-03) Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph P.
A spectrometer built using an external cavity pulsed quantum cascade laser is described. The spectrometer has a tuning range from 10 – 13 µm (1,000 – 769 cm−1) and is designed to target volatile organic compounds (VOCs) which often exhibit water-free molecular absorption within the region. The spectrometer utilizes a hollow silica waveguide gas cell which has an internal volume of a few millilitres, a fast response time (∼1 s), and is advantageous when only low sample volumes, similar to the cell volume, are available. Propane is used as a test gas because it is easy to handle, and its spectral profile is comparable to VOCs of interest. Its absorption in the region is primarily within the ν21 band which spans from 10.55 – 11.16 µm (948 – 896 cm−1). Spectral measurements at a range of concentrations show good linearity and an Allan deviation of absorbance values recorded over a 100-minute period indicates a minimum detectable absorbance of 3.5×10−5 at an integration time of 75 s.
Open Access
Low-coherence and broadband confocal refractometry: reducing the measurement time
(IOP Publishing, 2023-09-04) Francis, Daniel; Hallam, Jonathan M.; Tatam, Ralph P.
This paper describes the steps taken to improve the measurement speed of a combined low-coherence and confocal refractive index measurement system. The instrument measures the refractive index and thickness of transparent plates using a fibre-based low-coherence interferometer with a line-scan spectrometer. The spectrometer allows on-line dispersion measurement which is necessary to derive the sample thickness t as well as both the phase and group refractive indices np, ng. The measurements were performed on a sample with six surfaces consisting of three glass windows mounted in a lens tube. Experimental results show that a measurement time of 4.4 s for the multi-layered object, which has a total thickness of approximately 10.5 mm, can be achieved whilst maintaining an accuracy of better than 0.1% for np, ng, and t. This represents an approximately hundredfold improvement over previously published measurements.
Open Access
Low-volume, fast response-time hollow silica waveguide gas cells for mid-IR spectroscopy
(Optical Society of America, 2016-08-22) Francis, Daniel; Hodgkinson, Jane; Livingstone, B.; Black, Paul; Tatam, Ralph P.
Hollow silica waveguides (HSWs) are used to produce long path length, low-volume gas cells, and are demonstrated with quantum cascade laser spectroscopy. Absorption measurements are made using the intrapulse technique, which allows measurements to be made across a single laser pulse. Simultaneous laser light and gas coupling is achieved through the modification of commercially available gas fittings with low dead volume. Three HSW gas cell configurations with different path lengths and internal diameters are analyzed and compared with a 30 m path length astigmatic Herriott cell. Limit of detection measurements are made for the gas cells using methane at a wavelength 7.82 μm. The lowest limit of detection was provided by HSW with a bore diameter of 1000 μm and a path length of 5 m and was measured to be 0.26 ppm, with a noise equivalent absorbance of 4.1×10 −4 . The long-term stability of the HSW and Herriott cells is compared through analysis of the Allan–Werle variance of data collected over a 24 h period. The response times of the HSW and Herriott cells are measured to be 0.8 s and 36 s, respectively.
Open Access
A mechanically stable laser diode speckle interferometer for surface contouring and displacement measurement
(Institute of Physics, 2015-04-09) Francis, Daniel; Masiyano, Dackson; Hodgkinson, Jane; Tatam, Ralph P.
Electronic speckle pattern interferometry (ESPI) is demonstrated using a simple configuration consisting of a wedged window and a beamsplitter. The window serves to produce a reference beam which is in-line with the scattered object beam. The system is almost common-path and therefore provides much better mechanical stability than conventional ESPI configurations, which have widely separated beam paths. The configuration has collinear observation and illumination directions and therefore has maximum sensitivity to out-of-plane displacement. Wavelength modulation through adjustment of the laser diode control current provides a convenient method of phase shifting without the need for external moving parts. Further, variation of the laser diode control temperature allows extended wavelength tuning to adjacent longitudinal modes, facilitating surface contouring measurements via the two-wavelength technique. The interferometer is demonstrated for surface displacement measurement with a 3.3 μm centre displacement measured over a 15 mm × 15 mm region of a flat plate. Contour measurements of a shaped object are made using an equivalent wavelength of 1.38 mm.
Open Access
Mid-IR spectroscopic instrumentation for point-of-care diagnosis using a hollow silica waveguide gas cell
(International Society for Optics and Photonics - SPIE, 2017-02-17) Francis, Daniel; Hodgkinson, Jane; Walton, Christopher; Sizer, Jeremy; Black, Paul; Livingstone, Beth; Fowler, Dawn P.; Patel, Mitesh K.; Tatam, Ralph P.
Laser spectroscopy provides the basis of instrumentation developed for the diagnosis of infectious disease, via quantification of organic biomarkers that are produced by associated bacteria. The technology is centred on a multichannel pulsed quantum cascade laser system that allows multiple lasers with different wavelengths to be used simultaneously, each selected to monitor a different diagnostic biomarker. The instrument also utilizes a hollow silica waveguide (HSW) gas cell which has a very high ratio of interaction pathlength to internal volume. This allows sensitive detection of low volume gas species from small volume biological samples. The spectroscopic performance of a range of HSW gas cells with different lengths and bore diameters has been assessed using methane as a test gas and a best-case limit of detection of 0.26 ppm was determined. The response time of this cell was measured as a 1,000 sccm flow of methane passed through it and was found to be 0.75 s. These results are compared with those obtained using a multi-pass Herriot cell. A prototype instrument has been built and approved for clinical trials for detection of lung infection in acute-care patients via analysis of ventilator breath. Demonstration of the instrument for headspace gas analysis is made by monitoring the methane emission from bovine faeces. The manufacture of a hospital-ready device for monitoring biomarkers of infection in the exhaled breath of intensive care ventilator patients is also presented.
Open Access
Objective speckle velocimetry for autonomous vehicle odometry
(Osa Optical Society of America, 2012-05-31T00:00:00Z) Francis, Daniel; Charrett, Thomas O. H.; Waugh, L.; Tatam, Ralph P.
Speckle velocimetry is investigated as a means of determining odometry data with potential for application on autonomous robotic vehicles. The technique described here relies on the integration of translation measurements made by normalized cross-correlation of speckle patterns to determine the change in position over time. The use of objective (non-imaged) speckle offers a number of advantages over subjective (imaged) speckle, such as a reduction in the number of optical components, reduced modulation of speckles at the edges of the image, and improved light efficiency. The influence of the source/detector configuration on the speckle translation to vehicle translation scaling factor for objective speckle is investigated using a computer model and verified experimentally. Experimental measurements are presented at velocities up to 80 mms=1 which show accuracy better than 0.4%.
Open Access
An optical fiber hydrogen sensor using a palladium-coated ball lens
(Institute of Electrical and Electronics Engineers, 2015-06-15) Chowdhury, Sahar A.; Correia, Ricardo N.; Francis, Daniel; Brooks, Simon J.; Jones, Benjamin J. S.; Thompson, Alexander W. J.; Hodgkinson, Jane; Tatam, Ralph P.
A self-referenced optical fiber refractometer using a ball lens as a sensor head has been developed and characterized. A 350-μm ball lens created at the tip of a single mode fiber has been coated with a 40-nm optically thin layer of palladium that reacts with hydrogen to form a hydride, which has a lower reflectivity than pure palladium. Optical reflectance measurements from the tip of the ball lens were performed to determine the hydrogen response. The change in reflectivity is proportional to the hydrogen concentration in the range 0% to 1% hydrogen in air with a detection limit down to 10 ppm (1σ) in air. This technique offers a simple sensor head arrangement, with a larger sampling area (~40 times) than a typical single-mode fiber core. A statistical image analysis of a palladium film, with cracks created by accelerated failure, confirms that the anticipated sensor area for a ball lens sensor head has a more predictable reflectivity than that of a bare fiber core.

Browsing by Author "Francis, Daniel"

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