Wavelength Modulation Spectroscopy: Combined Frequency and Intensity Laser Modulation

Schilt, Stéphane; Thévenaz, Luc; Robert, Philippe A.

doi:10.1364/ao.42.006728

Cited by 267 publications

(176 citation statements)

References 30 publications

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“…Owen et al (2013) performed spectroscopic studies on relevant atmospheric absorbers in this region at reduced pressure to characterize the interferences. For openpath detection at ambient pressures, wavelength modulation spectroscopy is a well-suited detection technique for spectral resolution of these weak, overlapping absorption features (Schilt et al, 2003;Zondlo et al, 2010). As shown in Fig.…”

Section: Spectroscopymentioning

confidence: 99%

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

et al. 2014

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Abstract. We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric ammonia sensor operating at 9.06 µm for high-sensitivity, high temporal resolution, ground-based measurements. Atmospheric ammonia (NH 3 ) is a gas-phase precursor to fine particulate matter, with implications for air quality and climate change. Currently, NH 3 sensing challenges have led to a lack of widespread in situ measurements. Our open-path sensor configuration minimizes sampling artifacts associated with NH 3 surface adsorption onto inlet tubing and reduced pressure sampling cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic wavelength modulation spectroscopy allows for selective and sensitive detection of atmospheric pressurebroadened absorption features. An in-line ethylene reference cell provides real-time calibration (±20 % accuracy) and normalization for instrument drift under rapidly changing field conditions. The sensor has a sensitivity and noise-equivalent limit (1σ ) of 0.15 ppbv NH 3 at 10 Hz, a mass of ∼ 5 kg and consumes ∼ 50 W of electrical power. The total uncertainty in NH 3 measurements is 0.20 ppbv NH 3 ± 10 %, based on a spectroscopic calibration method. Field performance of this open-path NH 3 sensor is demonstrated, with 10 Hz time resolution and a large dynamic response for in situ NH 3 measurements. This sensor provides the capabilities for improved in situ gas-phase NH 3 sensing relevant for emission source characterization and flux measurements.

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Section: Spectroscopymentioning

confidence: 99%

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

et al. 2014

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“…The detector signal was demodulated at harmonics of the modulation frequency (40 kHz) to minimize laser excess noise by shifting the detection bandwidth to higher frequencies (Schilt et al 2003). Figure 3 shows the WMS spectra within the laser scan range.…”

Section: Sensor Designmentioning

confidence: 99%

Long-Path Quantum Cascade Laser–Based Sensor for Methane Measurements

Michel

Miller

Sun

et al. 2016

Journal of Atmospheric and Oceanic Technology

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A long-path methane (CH 4 ) sensor was developed and field deployed using an 8-mm quantum cascade laser. The high optical power (40 mW) of the laser allowed for path-integrated measurements of ambient CH 4 at total pathlengths from 100 to 1200 m with the use of a retroreflector. Wavelength modulation spectroscopy was used to make high-precision measurements of atmospheric pressure-broadened CH 4 absorption over these long distances. An in-line reference cell with higher harmonic detection provided metrics of system stability in rapidly changing and harsh environments. The system consumed less than 100 W of power and required no consumables. The measurements intercompared favorably (typically less than 5% difference) with a commercial in situ methane sensor when accounting for the different spatiotemporal scales of the measurements. The sensor was field deployed for 2 weeks at an arctic lake to examine the robustness of the approach in harsh field environments. Shortterm precision over a 458-m pathlength was 10 ppbv at 1 Hz, equivalent to a signal from a methane enhancement above background of 5 ppmv in a 1-m length. The sensor performed well in a range of harsh environmental conditions, including snow, rain, wind, and changing temperatures. These field measurements demonstrate the capabilities of the approach for use in detecting large but highly variable emissions in arctic environments.

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“…It happens when light radiation interacts with molecular species and it is represented by the Beer-Lambert Law [23,24]:…”

Section: Wavelength Modulation Spectroscopymentioning

confidence: 99%

Ammonia sensing system based on wavelength modulation spectroscopy

et al. 2015

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A sensing system in the near infrared region has been developed for ammonia sensing based on the wavelength modulation spectroscopy (WMS) principle. The WMS is a rather sensitive technique for detecting atomic/molecular species, presenting the advantage that it can be used in the near-infrared region by using the optical telecommunications technology. In this technique, the laser wavelength and intensity were modulated by applying a sine wave signal through the injection current, which allowed the shift of the detection bandwidth to higher frequencies where laser intensity noise was typically lower. Two multi-pass cells based on free space light propagation with 160 cm and 16 cm of optical path length were used, allowing the redundancy operation and technology validation. This system used a diode laser with an emission wavelength at 1512.21 nm, where NH 3 has a strong absorption line. The control of the NH 3 gas sensing system, as well as acquisition, processing and data presentation was performed.

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Wavelength Modulation Spectroscopy: Combined Frequency and Intensity Laser Modulation

Cited by 267 publications

References 30 publications

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

Long-Path Quantum Cascade Laser–Based Sensor for Methane Measurements

Ammonia sensing system based on wavelength modulation spectroscopy

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