Dr. Christopher R. Howle Profile

Dr. Christopher R. Howle

Senior Principal Scientist at Defence Science and Technology Lab

SPIE Involvement:

Conference Chair | Editor | Author

Publications (32)

Proceedings Article | 26 June 2024 Paper

Trace explosive detection and identification signature characterization studies using deep-UV fluorescence and Raman spectroscopy

Jayne Newton, Elisa Falconer, Ellie Makinson, Bethany Bowden, Sonali Dabba, Natasha Stevens, Chris Howle, Rohit Bhartia, William Hug, Ray Reid

Proceedings Volume 13056, 1305604 (2024) https://doi.org/10.1117/12.3015055

KEYWORDS: Raman spectroscopy, Explosives, Fluorescence, Deep ultraviolet, Mixtures, Explosives detection

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Proceedings Article | 7 June 2024 Presentation + Paper

Stand-off explosive sensing and imaging with scanning dual-comb IR spectrometer: limits of detection and operation in scanning mode

Vasili Savitski, James Feehan, Roman Spesyvtsev, Kerry Alton, Peter Glover, Lauren Holley, Jayne Newton, Chris Howle, Michael Papantonakis, Andrew McGill, Viet Nguyen

Proceedings Volume 13056, 1305613 (2024) https://doi.org/10.1117/12.3014271

KEYWORDS: Spectroscopy, Correlation coefficients, Explosives, Infrared spectroscopy, Detection and tracking algorithms, Signal detection

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Proceedings Article | 14 June 2023 Presentation + Paper

Stand-off explosive sensing and imaging with scanning dual-comb IR spectrometer: extended spectral range and speckle management

Vasili Savitski, Jakob Hayden, James Feehan, Roman Spesyvtsev, Raphael Horvath, Markus Geiser, Kerry Alton, Peter Glover, Lauren Holley, Jayne Newton, Chris Howle, Michael Papantonakis, Andrew McGill, Viet Nguyen, Paulina Moussavi, Thoi Nguyen

Proceedings Volume 12541, 125410D (2023) https://doi.org/10.1117/12.2666007

KEYWORDS: Speckle, Spectroscopy, Quantum cascade lasers, Laser frequency, Signal detection, Explosives

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Proceedings Article | 30 May 2022 Presentation + Paper

Detection of chemical liquid hazards on surfaces using biomimetic stand-off sensing

Scott Rogers, Chris Howle, Ken McEwan, Kevin Major, Brandon Shaw, Kenneth Ewing

Proceedings Volume 12116, 121160N (2022) https://doi.org/10.1117/12.2622900

KEYWORDS: Liquids, Sensors, Infrared radiation, Electronic filtering, Chemical weapons, Optical filters, Mirrors, Infrared spectroscopy, Biomimetics

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Proceedings Article | 30 May 2022 Presentation

Combined deep-UV induced fluorescence multispectral imaging and resonance-Raman: a dual modality approach for rapid location and identification of in-theatre biological contaminants

David J. Stothard, John Leck, Marek Michalowski, Paul Murray, Stephen Marshall, Kelly Curtis, Chris Howle, William Brooks, Michael Foster

Proceedings Volume PC12116, PC1211609 (2022) https://doi.org/10.1117/12.2621607

KEYWORDS: Raman spectroscopy, Luminescence, Deep ultraviolet, Multispectral imaging, Contamination, Spectroscopy, Spatial resolution, Sensors, Scene classification, Heterodyning

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Proceedings Article | 15 April 2021 Presentation + Paper

Detection of chemical threats on surfaces using a human color vision inspired sensing method

Kevin Major, Jasbinder Sanghera, L. Shaw, Chris Howle, Ken McEwan, Kenneth Ewing

Proceedings Volume 11749, 117490L (2021) https://doi.org/10.1117/12.2589553

KEYWORDS: Color vision, Sensors, Infrared sensors, Biological and chemical sensing, Optical filters, Nerve agents, Infrared radiation, Infrared detectors, Environmental sensing, Chemical fiber sensors

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Proceedings Article | 12 April 2021 Presentation + Paper

Sensing of bacterial spores with 2D-IR spectroscopy

Barbara Procacci, Samantha Rutherford, Gregory Greetham, Michael Towrie, Anthony Parker, Camilla Robinson, Christopher Howle, Neil Hunt

Proceedings Volume 11749, 117490C (2021) https://doi.org/10.1117/12.2585894

KEYWORDS: Spectroscopy, Bacteria, Ultrafast laser spectroscopy, Statistical analysis, Reflection, Proteins, Molecules, Molecular spectroscopy, Molecular biology, Library classification systems

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Proceedings Article | 12 April 2021 Presentation + Paper

A compact fiber-laser-based system for detection of biological agents via coherent Raman spectroscopy

N. Coluccelli, P. Laporta, G. Cerullo, K. Curtis, K. McEwan, C. Howle

Proceedings Volume 11749, 117490D (2021) https://doi.org/10.1117/12.2590001

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SPIE Journal Paper | 11 November 2020 Open Access

Applications of compressive sensing in spatial frequency domain imaging

Ben O. Mellors, Alexander Bentley, Abigail Spear, Christopher Howle, Hamid Dehghani

JBO, Vol. 25, Issue 11, 112904, (November 2020) https://doi.org/10.1117/12.10.1117/1.JBO.25.11.112904

KEYWORDS: Optical properties, Compressed sensing, Data acquisition, Image compression, Image restoration, Image analysis, Calibration, Tissue optics, Spatial frequencies, Reconstruction algorithms

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Proceedings Article | 24 April 2020 Presentation + Paper

Enhancing hybrid metal-semiconductor systems beyond SERS with PIERS (photo-induced enhanced Raman scattering) for trace analyte detection

D. Glass, E. Cortés, W. Peveler, C. Howle, R. Quesada-Cabrera, I. Parkin, S. Maier

Proceedings Volume 11416, 1141602 (2020) https://doi.org/10.1117/12.2557517

KEYWORDS: Raman spectroscopy, Ultraviolet radiation, Ultraviolet light emitting diodes, Ultraviolet sources, Surface enhanced Raman spectroscopy, Molecular spectroscopy, Chemical detection, Semiconductors

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Proceedings Article | 24 April 2020 Presentation + Paper

Towards standoff photothermal spectroscopy of CBRNE hazards using an ultra-fast tunable QCL

J. Miles, M. Muir, S. W. J. Scully, I. Hunter, C. McIlroy, J. Cunningham, C. Robinson, C. Howle

Proceedings Volume 11416, 114160A (2020) https://doi.org/10.1117/12.2558085

KEYWORDS: Quantum cascade lasers, Modulation, Spectroscopy, Laser Doppler velocimetry, Absorption, Acousto-optics, Ultrafast phenomena, Acoustics, Continuous wave operation, Pulsed laser operation

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Proceedings Article | 19 July 2019 Paper

Cell trauma detection using infra-red live cell imaging

Ben O. Mellors, Hamid Dehghani, Christopher Howle, Abigail Spear

Proceedings Volume 11073, 110730M (2019) https://doi.org/10.1117/12.2525012

KEYWORDS: Live cell imaging, Infrared imaging, Infrared spectroscopy, Interfaces, Cell death, Wound healing, Mid-IR, FT-IR spectroscopy, Infrared radiation

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Proceedings Article | 17 May 2019 Presentation + Paper

Standoff hyperspectral imaging of CWAs and explosives using eyesafe quantum cascade laser arrays

Mark Witinski, Brandt Pein, Romain Blanchard, Gokhan Ulu, Greg Vander Rhodes, Kalyani Krishnamurthy, Chris Howle, Linda Lee, Rhea Clewes, Siobhan Conner, Daryoosh Vakhshoori

Proceedings Volume 11010, 1101003 (2019) https://doi.org/10.1117/12.2517760

KEYWORDS: Quantum cascade lasers, Signal to noise ratio, Spectroscopy, Infrared radiation, Sensors, Hyperspectral imaging, Long wavelength infrared, Standoff detection, Reflectivity, Chemical analysis

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Proceedings Article | 17 May 2019 Presentation + Paper

Photo-induced enhanced Raman spectroscopy (PIERS): sensing atomic-defects, explosives and biomolecules

D. Glass, E. Cortés, S. Ben-Jaber, T. Brick, R. Quesada-Cabrera, W. Peveler, Y. Zhu, C. Blackman, C. Howle, I. Parkin, S. Maier

Proceedings Volume 11010, 110100D (2019) https://doi.org/10.1117/12.2518948

KEYWORDS: Raman spectroscopy, Nanoparticles, Particles, Surface enhanced Raman spectroscopy, Molecules, Oxygen, Ultraviolet radiation, Semiconductors, Scanning electron microscopy, Line scan image sensors

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Proceedings Article | 17 May 2019 Paper

Fiber-lasers for coherent Raman detection of toxic chemical hazards

N. Coluccelli, A. Gambetta, E. Vicentini, P. Laporta, K. McEwan, C. Howle

Proceedings Volume 11010, 1101015 (2019) https://doi.org/10.1117/12.2518847

KEYWORDS: Raman spectroscopy, Interferometers, Spectroscopy, Fourier transforms, Amplifiers, Chemical weapons, Cyanide, Ytterbium

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Proceedings Article | 4 March 2019 Paper

Mid-infrared spectroscopic imaging to assess wounded tissue health

Ben O. Mellors, Hamid Dehghani, Christopher Howle, Abigail Spear

Proceedings Volume 10873, 108730U (2019) https://doi.org/10.1117/12.2507215

KEYWORDS: Wound healing, FT-IR spectroscopy, Principal component analysis, Mid-IR, Imaging spectroscopy, Tissue optics, Spectroscopy

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Proceedings Article | 23 May 2018 Paper

Enabling standoff detection of hazardous materials using a fiber optic coupled quantum cascade infrared laser system

Kenneth Ewing, Kevin Major, Jasbinder Sanghera, Rafael Gattass, L. Brandon Shaw, Lynda Busse, David Arnone, Enrique Lopez, Michael Pushkarsky, Justin Kane, Rhea Clewes, Linda Lee, Chris Howle

Proceedings Volume 10629, 106290A (2018) https://doi.org/10.1117/12.2304352

KEYWORDS: Quantum cascade lasers, Standoff detection, Explosives, Infrared spectroscopy, Cameras, Optical fibers, Infrared radiation, Long wavelength infrared, Sensors

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Proceedings Article | 24 October 2016 Paper

Stand-off detection of aerosols using mid-infrared backscattering Fourier transform spectroscopy

L. Maidment, Z. Zhang, M. Bowditch, C. Howle, D. Reid

Proceedings Volume 9995, 999508 (2016) https://doi.org/10.1117/12.2241052

KEYWORDS: Aerosols, Atmospheric particles, Optical parametric oscillators, Mid-IR, Scattering, Absorption, Spectroscopy, Light scattering, Mie scattering, Laser scattering

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Proceedings Article | 12 May 2016 Paper

Application of the modified transient plane source technique for early detection of liquid explosives

Robert Bateman, Adam Harris, Linda Lee, Christopher Howle, Sarah L. Ackermann

Proceedings Volume 9824, 98240J (2016) https://doi.org/10.1117/12.2224174

KEYWORDS: Explosives, Explosives detection, Liquids, Aluminum, Sensors, Convection, Polishing, Transportation security, Calibration, Spectroscopy

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Proceedings Article | 7 March 2016 Paper

Monitoring combat wound healing by IR hyperspectral imaging

Chris Howle, Abigail Spear, Ehsan Gazi, Nicole Crane

Proceedings Volume 9703, 97031E (2016) https://doi.org/10.1117/12.2213330

KEYWORDS: Infrared imaging, Wound healing, Optical parametric oscillators, Hyperspectral imaging, Injuries, Imaging spectroscopy, Imaging systems, Spectroscopy, Tissues, Mirrors, Absorption, FT-IR spectroscopy, Mid-IR, Biopsy

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Proceedings Article | 22 October 2015 Paper

Stand-off detection of liquid thin films using active mid-infrared hyperspectral imaging

L. Maidment, Z. Zhang, C. Howle, S. Lee, A. Christie, D. Reid

Proceedings Volume 9648, 964804 (2015) https://doi.org/10.1117/12.2197586

KEYWORDS: Hyperspectral imaging, Liquids, Mid-IR, Optical parametric oscillators, Cameras, Absorption, Imaging systems, Thin films, Long wavelength infrared, FT-IR spectroscopy

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Proceedings Article | 29 May 2014 Paper

Active FTIR-based standoff detection in the 3-4 micron region using broadband femtosecond optical parametric oscillators

Derryck Reid, Zhaowei Zhang, Christopher Howle

Proceedings Volume 9073, 907302 (2014) https://doi.org/10.1117/12.2053227

KEYWORDS: Optical parametric oscillators, Spectroscopy, FT-IR spectroscopy, Mid-IR, Femtosecond phenomena, Absorption, Solids, Aluminum, Spatial coherence, Explosives

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Proceedings Article | 29 May 2014 Paper

Development of an ultrahigh-performance infrared detector platform for advanced spectroscopic sensing systems

Manish Jain, Gary Wicks, Andrew Marshall, Adam Craig, Terry Golding, Khalid Hossain, Ken McEwan, Chris Howle

Proceedings Volume 9073, 907304 (2014) https://doi.org/10.1117/12.2054328

KEYWORDS: Sensors, Diodes, Infrared detectors, Infrared sensors, Detector development, Infrared radiation, Mercury cadmium telluride, Spectroscopy, Diffusion, Indium gallium arsenide

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Proceedings Article | 29 May 2013 Paper

Mid-wave infrared hyperspectral imaging of unknown chemical warfare agents

Rhea Clewes, Chris Howle, Jason Guicheteau, Darren Emge, Keith Ruxton, Gordon Robertson, William Miller, Graeme Malcolm, Gareth Maker

Proceedings Volume 8710, 871002 (2013) https://doi.org/10.1117/12.2017868

KEYWORDS: Mid-IR, Sensors, Short wave infrared radiation, Liquids, Metals, Absorption, Infrared spectroscopy, Mirrors, Optical parametric oscillators

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Proceedings Article | 30 October 2012 Paper

Stand-off spectroscopy for the detection of chemical warfare agents

Rhea Clewes, Chris Howle, David J. Stothard, Malcolm Dunn, Gordon Robertson, William Miller, Graeme Malcolm, Gareth Maker, Rick Cox, Brad Williams, Matt Russell

Proceedings Volume 8546, 85460X (2012) https://doi.org/10.1117/12.974574

KEYWORDS: Raman spectroscopy, Photons, Imaging systems, Sensors, Spectroscopy, Liquids, Blistering agents, Optical parametric oscillators, Crystals

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The most desirable configuration for detection of toxic chemicals utilises the maximum distance between detector and hazard. This approach minimises the contamination of equipment or personnel. Where the target chemical is an involatile liquid, indirect detection of the liquid contamination is made difficult by inherently low vapour pressure. In this instance, direct detection of the chemical hazard is the best approach. Recent technology developments have allowed spectroscopic systems to provide multiple options for the stand-off detection of involatile chemical warfare agents (CWAs). Two different stand-off spectroscopic systems, based upon IR absorption and Raman spectroscopic techniques are described here. The Negative Contrast Imager (NCI) is based upon an optical parametric oscillator (OPO) source comprising a Q-switched intracavity MgO:PPLN crystal. This crystal has a fanned grating design and wavelength tuning is achieved by translating the PPLN crystal within the 1064 nm pump beam. This approach enables the production of shortwave and midwave IR radiation (1.5 – 1.8 μm and 2.6 – 3.8 μm, respectively), which is scanned across the scene of interest. Target materials that have an absorption feature commensurate with the wavelength of incoming radiation reduce the intensity of returned signal, resulting in dark pixels in the acquired image. This method enables location and classification of the target material. Stand-off Raman spectroscopy allows target chemicals to be identified at range through comparison of the acquired signature relative to a spectral database. In this work, we used a Raman system based upon a 1047 nm Nd:YLF laser source and a proprietary InGaAsP camera system. Utilisation of a longer excitation wavelength than most conventional stand-off detection systems (e.g. 532 or 785 nm) enables reduction of fluorescence from both the surface and the deposited chemicals, thereby revealing the Raman spectrum. NCI and Raman spectroscopy are able to detect CWAs on surfaces at distances of 2 – 10 metres and have potential to detect over longer ranges. We report the successful identification of at least 60 μl of nitrogen mustard at a distance of a 2 m and 10 m using NCI and Raman spectroscopy.

Proceedings Article | 30 October 2012 Paper

Infrared hyperspectral imaging for chemical vapour detection

K. Ruxton, G. Robertson, W. Miller, G.P. Malcolm, G. Maker, C. Howle

Proceedings Volume 8546, 85460K (2012) https://doi.org/10.1117/12.975057

KEYWORDS: Absorption, Mid-IR, Optical parametric oscillators, Infrared imaging, Hyperspectral imaging, Mirrors, Short wave infrared radiation, Infrared spectroscopy, Image processing

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Proceedings Article | 13 October 2011 Paper

Remote detection of liquid surface contamination by imaging infrared spectroscopy: measurements and modelling

René Braun, Jens Eichmann, Samer Sabbah, Roland Harig, Chris Howle

Proceedings Volume 8189, 81890G (2011) https://doi.org/10.1117/12.899065

KEYWORDS: Liquids, Temperature metrology, Infrared spectroscopy, Spectroscopy, Reflectivity, Signal to noise ratio, Contamination, Absorption, Reflection, Imaging spectroscopy

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Proceedings Article | 13 October 2011 Paper

Spatially offset Raman spectroscopy (SORS) for through-barrier proximal chemical and explosive detection

Alex Frisby, Linda Lee, Chris Howle, Andy Martin, Rebecca Hopkins

Proceedings Volume 8189, 81890B (2011) https://doi.org/10.1117/12.898611

KEYWORDS: Raman spectroscopy, Signal to noise ratio, Signal detection, Luminescence, Urea, Explosives, Sensors, Glasses, Explosives detection, Chemical analysis

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Proceedings Article | 6 October 2011 Paper

Hazardous liquid detection by active hyperspectral imaging

Chris Howle, Alexander Frisby, Alastair J. McIntosh, David J. Stothard, Malcolm Dunn, Gordon Robertson, William Miller, Graeme Malcolm, Gareth Maker

Proceedings Volume 8189, 81890H (2011) https://doi.org/10.1117/12.898516

KEYWORDS: Mid-IR, Optical parametric oscillators, Mirrors, Crystals, Absorption, Liquids, Hyperspectral imaging, Short wave infrared radiation, Laser crystals, Sensors

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Proceedings Article | 2 October 2008 Paper

Remote detection of liquids by Raman line imaging

Chris Howle, Christopher Dyer, Kurt Baldwin, Richard White

Proceedings Volume 7116, 71160S (2008) https://doi.org/10.1117/12.799832

KEYWORDS: Raman spectroscopy, Computing systems, Image intensifiers, Electron multiplying charge coupled devices, Pulsed laser operation, Q switched lasers, Q switching, Zoom lenses, Spectrographs, Liquids

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Proceedings Article | 17 April 2008 Paper

Active hyperspectral imaging system for the detection of liquids

Chris Howle, David J. Stothard, Cameron Rae, Mark Ross, Ben Truscott, Christopher Dyer, Malcolm Dunn

Proceedings Volume 6954, 69540L (2008) https://doi.org/10.1117/12.787452

KEYWORDS: Absorption, Optical parametric oscillators, Mirrors, Liquids, Mid-IR, Nonlinear crystals, Crystals, Sensors, Spectroscopy, Imaging systems

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Proceedings Article | 16 April 2008 Paper

Remote identification of liquid surface contamination by imaging Fourier transform spectrometry

Roland Harig, René Braun, Chris Dyer, Chris Howle, Ben Truscott

Proceedings Volume 6954, 69540G (2008) https://doi.org/10.1117/12.780602

KEYWORDS: Liquids, Fourier transforms, Spectroscopy, Radiative transfer, Reflection, Temperature metrology, Contamination, Solids, Infrared spectroscopy, Signal to noise ratio

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