Beam displacement as a function of temperature and turbulence length scale at two different laser radiation wavelengths

Isterling, William M; Dally, Bassam B.; Alwahabi, Zeyad T.; Dubovinsky, Miro; Wright, Daniel Nilsen

doi:10.1364/ao.51.000055

Cited by 3 publications

(2 citation statements)

References 25 publications

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“…Of greater utility is work considering the propagation of laser-based IR countermeasures through the protected aircraft's own exhaust, e.g. [12,13].…”

Section: System Overviewmentioning

confidence: 99%

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

Wright

McCormick

Ozanyan

et al. 2015

2015 IEEE Aerospace Conference

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Abstract-We report on the development of three systems intended to provide fast, non-intrusive measurement of cross sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine.We describe a CO2 imaging system that performs wavelength modulation spectroscopy (WMS) simultaneously on 126 beam paths. Its novel architecture uses a Tm-doped fiber amplifier to generate sufficient optical power for the entire beam array (> 3 W) from a single 1997.2 nm diode-laser seed, reducing cost and enabling fully parallel detection and signal recovery. Various optical propagation issues are considered, including those arising from the varying degrees of interaction with the exhaust flow that exist within the beam array, as well as pointing errors arising from the limited rigidity of the measurement system's structure.We also report first steps towards a similar UHC measurement system, operating in the mid-infrared (MIR) region and targeting partially decomposed or oxidized fuel constituents, including formaldehyde and propene. Progress towards the chalcogenide glasses and fibers, needed for light delivery and/or amplification at these wavelengths is described. Finally, we report on the development status of a tomographic soot imaging system, based on laser induced incandescence (LII). We have demonstrated both long (192 ns) and short (17 ns) pulse variants of LII using fiber laser sources. Single path tests on a laboratory soot generator and, in the long pulse case, on a jet engine have confirmed that the energy and beam quality available from the fiber lasers is sufficient to enable an autoprojection approach, using just two intensified CCD cameras having 'near-orthogonal' views, with respect to the excitation laser.

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“…Of greater utility is work considering the propagation of laser-based IR countermeasures through the protected aircraft's own exhaust, e.g. [12,13].…”

Section: System Overviewmentioning

confidence: 99%

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

Wright

McCormick

Ozanyan

et al. 2015

2015 IEEE Aerospace Conference

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“…Fire generates random fluctuations in the refractive index due to convective flow of heat along the beams propagation path [13], which creates random fluctuations in the refractive index, resulting in beam distortion, phase changes and beam displacement and tilt. The temporal and spatial variation of the laser beam can therefore be measured as intensity variations, phase changes, beam wander, or beam spread changes [4,9,14,15]. Different reports have been made on heat/fire detectors that sense the movement of hot gases due to the fire causing refraction of the beam either toward or away from the optical detector.…”

Section: Introductionmentioning

confidence: 99%

Simple and robust speckle detection method for fire and heat detection in harsh environments

Christensen

Zainchkovskyy²,

Barrera‐Figueroa³

et al. 2019

Appl. Opt.

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Standard laser based fire detection systems are often based on measuring variation of optical signal amplitude. However, mechanical noise interference and loss from dust and steam can obscure the detection signal, resulting in faulty results or inability to detect a potential fire. The presented fire detection technology will allow the detection of fire in harsh and dusty areas, which are prone to fires, where current systems show limited performance or are unable to operate. It is not the amount of light nor its wavelength that is used for detecting fire, but how the refractive index randomly fluctuates due to the heat convection from the fire. In practical terms this means that light obstruction from ambient dust particles will not be a problem as long as a small fraction of the light is detected and that fires without visible flames can still be detected. The standalone laser system consists of a Linux-based Red Pitaya system, a cheap 650 nm laser diode, and a PIN photo-detector. Laser light propagates through the monitored area and reflects off a retroreflector generating a speckle pattern. Every 3 seconds time traces and frequency noise spectra are measured and 8 descriptors are deduced to identify a potential fire. Both laboratory and factory acceptance tests have been performed with success.

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Spatial-Dynamic Characteristics Research of a Laser Beam at Interacting with Thermal Convection Flow

Kazakov,

Paraskun,

Ryvkina

et al. 2024

2024 Wave Electronics and Its Application in Information and Telecommunication Systems (WECONF)

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Beam displacement as a function of temperature and turbulence length scale at two different laser radiation wavelengths

Cited by 3 publications

References 25 publications

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

Simple and robust speckle detection method for fire and heat detection in harsh environments

Spatial-Dynamic Characteristics Research of a Laser Beam at Interacting with Thermal Convection Flow

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