Atmospheric pressure monitoring of trace gases using tunable diode lasers

Cassidy, Daniel T.; Reid, J.

doi:10.1364/ao.21.001185

Cited by 228 publications

(82 citation statements)

References 11 publications

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“…Coincident with the 100-Hz modulation was a small-amplitude but higher frequency modulation («20 kHz) taken from the sine output of a SRS Model 830 DSP lock-in amplifier. The application of the two modulations to the laser diode current facilitated wavelength modulation spectroscopy (i.e., 2f detection), which was needed for enhanced signal sensitivity [10][11][12][13][14]. Wavelength modulation spectroscopy is convenient for analysis because of the linear relationship that exists between the measured absorption signal and the analyte's concentration.…”

Section: Methodsmentioning

confidence: 99%

Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires Extinguished by FE-36 and FE-36 Plus APP

Skaggs¹,

Daniel²,

Miziolek³

et al. 2000

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Tunable diode laser absorption spectroscopy (TDLAS) is used to measure the time evolution of hydrogen fluoride (HF) concentrations produced from a series of enclosed heptane/air pan fires extinguished by FE-36 or FE-36 plus ammonium polyphosphate (APP). Recent advances in room-temperature fiber-coupled near-infrared (NIR) diode lasers provide isolation of the laser and signal-processing electronics from the hostile sampling site. For the fires studied, the change in HF gas concentration with time is dependent upon the fire-fighting chemical used to extinguish the fire. The presence of APP is observed to accelerate the dissipation of HF from the fire enclosure. Visible attenuation spectroscopy is also used to measure the amount of light attenuation (obscuration) that occurs as a hand-held fire extinguisher containing powder fire-fighting agent is released in the crew space of a Ml-Abrams land combat vehicle. Obscuration tests demonstrate that release of APP from extinguishers in an occupied space does not present a visibility challenge to the vehicle personnel.

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Section: Methodsmentioning

confidence: 99%

Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires Extinguished by FE-36 and FE-36 Plus APP

Skaggs¹,

Daniel²,

Miziolek³

et al. 2000

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“…The basic sensor design includes a VCSEL (to measure CO 2 , CH 4 and H 2 O at 2,004 nm, 1,654 nm and 1,854 nm wavelengths, respectively), a cylindrical multi-pass cell [19] for appropriate optical pathlength (0.1-20 m), and a 2.2 µm extended InGaAs photodetector and laser drive, detection and signal processing electronics. The WMS measurement technique has been described in detail previously [14][15][16][17]. The tunable diode laser is tuned to near an absorption line by controlling its temperature and the injected DC current.…”

Section: Sensor Designmentioning

confidence: 99%

“…The most suitable absorption line transitions available within spectral coverage of commercial VCSELs were used to maximize performance. In order to enhance the sensitivity and time response of the sensor we employ wavelength modulation spectroscopy (WMS) [9,[14][15][16][17], which inherently reduces any backgrounds associated with parasitic laser scanning and modulating effects and interfering molecular transitions. For example, in a typical IR spectrum there are several regions of significant overlap from water vapor molecular transitions.…”

Section: Introductionmentioning

confidence: 99%

Low Power Greenhouse Gas Sensors for Unmanned Aerial Vehicles

et al. 2012

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Abstract:We demonstrate compact, low power, lightweight laser-based sensors for measuring trace gas species in the atmosphere designed specifically for electronic unmanned aerial vehicle (UAV) platforms. The sensors utilize non-intrusive optical sensing techniques to measure atmospheric greenhouse gas concentrations with unprecedented vertical and horizontal resolution (~1 m) within the planetary boundary layer. The sensors are developed to measure greenhouse gas species including carbon dioxide, water vapor and methane in the atmosphere. Key innovations are the coupling of very low power vertical cavity surface emitting lasers (VCSELs) to low power drive electronics and sensitive multi-harmonic wavelength modulation spectroscopic techniques. The overall mass of each sensor is between 1-2 kg including batteries and each one consumes less than 2 W of electrical power. In the initial field testing, the sensors flew successfully onboard a T-Rex Align 700E robotic helicopter and showed a precision of 1% or less for all three trace gas species. The sensors are battery operated and capable of fully automated operation for long periods of time in diverse sensing environments. Laser-based trace gas sensors for UAVs allow for high spatial mapping of local greenhouse gas OPEN ACCESSRemote Sens. 2012, 4 1356 concentrations in the atmospheric boundary layer where land/atmosphere fluxes occur. The high-precision sensors, coupled to the ease-of-deployment and cost effectiveness of UAVs, provide unprecedented measurement capabilities that are not possible with existing satellite-based and suborbital aircraft platforms.

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“…Wavelength modulation spectroscopy (WMS), as briefly discussed in the introduction, provides advantages for sensitive measurements in environments with a high degree of temporal variability (Cassidy and Reid 1982). In WMS, a sinusoidal current modulation is added to the sweep variation employed in direct absorption, such that the drive current for the laser over one period of the sweep is described by:…”

Section: Theoretical Basis For Wavelength Modulation Absorption Measumentioning

confidence: 99%

“…This change can be extremely difficult to detect, and generally in clean . In addition direct absorption requires the use of dispersive optics or beamsplitters to separate the various laser beams; for a system with 6-8 measurement components with closely spaced transitions, these can be cumbersome and highly inefficient.Wavelength modulation spectroscopy (WMS), as briefly discussed in the introduction, provides advantages for sensitive measurements in environments with a high degree of temporal variability (Cassidy and Reid 1982). In WMS, a sinusoidal current modulation is added to the sweep variation employed in direct absorption, such that the drive current for the laser over one period of the sweep is described by:…”

mentioning

confidence: 99%

Multiplexed Sensor for Synthesis Gas Compsition and Temperature

Buckley

Gharavi²,

Leon³

2007

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The overall goal of this project has been to develop a highly sensitive, multiplexed TDL-based sensor for CO 2 , CO, H 2 O (and temperature), CH 4 , H 2 S, and NH 3 .Such a sensor was designed with so-called "plug-and-play" characteristics to accommodate additional sensors, and provided in situ pathintegrated measurements indicative of average concentrations at speeds suitable for direct gasifier control. The project developed the sensor and culminated in a real-world test of the underlying technology behind the sensor. During the project, new underlying measurements of spectroscopic constants for all of the gases of interest performed, in custom cells built for the project. The envisioned instrument was built from scratch from component lasers, fiber optics, amplifier blocks, detectors, etc. The sensor was tested for nearly a week in an operational power plant. The products of this research are expected to have a direct impact on gasifier technology and the production of high-quality syngas, with substantial broader application to coal and other energy systems. This report is the final technical report on project #DE-FG26-04NT42172. During the project we completed all of the milestones planned in the project, with a modification of milestone (7) required due to lack of funding and personnel.UCSD / Buckley #DE-FG26-04NT42172Final Technical Report p4 2. Executive SummaryThis project was to design, build, and test an integrated sensor that could be used to measure and control the products of coal gasification. The first milestone completed was the selection of experimental parameters, particularly the wavelengths for measurement of the desired species (H 2 O, CH 4 , CO, CO 2 , H 2 S, and NH 3 ). This was accomplished using software databases, careful inspection for interferences, particularly from hot H 2 O bands, and the availability of laser sources.The design and construction milestones involved hardware design choices, followed by assembling and testing of hardware. The sensor design and construction milestones were completed in the first year of the project, as planned.The measurement of temperature-and pressure-dependent spectroscopic parameters for the molecules and specific transitions of interest were monumental, time-consuming tasks. For these measurements, several long-path spectroscopic cells (one high pressure, one atmospheric and lower-pressure, two all-glass cells) were designed and built. Full spectroscopic understandingmeasurement of all of the relevant pressure broadening and line strength parameters at a range of pressures from 0-10 bar and temperatures up to 800 K was achieved for the CO, CO 2 , CH 4 , and H 2 O transitions selected for the sensor. Detailed and difficult similar measurements were also completed for NH 3 . Based on these measurements, highly accurate concentration measurement of these five gases is possible. Based on a more limited set of parameter measurements, qualitative measurement of H 2 S is also possible. The gas-handling requirements related to the toxicity of ...

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Atmospheric pressure monitoring of trace gases using tunable diode lasers

Cited by 228 publications

References 11 publications

Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires Extinguished by FE-36 and FE-36 Plus APP

Diode Laser Measurements of HF Concentrations From Heptane/Air Pan Fires Extinguished by FE-36 and FE-36 Plus APP

Low Power Greenhouse Gas Sensors for Unmanned Aerial Vehicles

Multiplexed Sensor for Synthesis Gas Compsition and Temperature

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