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A new signal processing algorithm tailored for in-situ applications combines multivariate analysis and hmable diode laser absorption spectroscopy. The principle and the application to the spectra separation of tetrafluoromethane and its interferants is demonstrated.

Monitoring of perfluorocarbon (PFC) evolution from aluminium smelting is gaining attention, not only because of their high greenhouse gas potentials but also due to process optimization purposes. Conventionally, PFC monitoring has been conducted by extractive sampling and subsequent analysis by fourier transform infrared (FTIR) spectroscopy. With FTIR, the quantification can be performed by IR spectral features specific for PFC. The downside is a requirement of gas scrubbing to remove HF detrimental to the instrument as well as relatively poor gas dynamics due to the large internal gas volume of the instrument. With emerging quantum cascade laser (QCL) technology, online monitoring can now be conducted with duct mounted lasers with calcium fluoride optical windows. However, due to a strong spectral overlap of CF4 and other gas constituents present in the process (e.g. methane), the QCL instruments currently suffer from some cross-interference. In this work, QCL single cell PFC monitoring has been validated by simultaneous monitoring with FTIR.

A laser-based hydrogen (H2) sensor using wavelength modulation spectroscopy (WMS) was developed for the contactless measurement of molecular hydrogen. The sensor uses a distributed feedback (DFB) laser to target the H2 quadrupole absorption line at 2121.8 nm. The H2 absorption line exhibited weak collisional broadening and strong collisional narrowing effects. Both effects were investigated by comparing measurements of the absorption linewidth with detailed models using different line profiles including collisional narrowing effects. The collisional broadening and narrowing parameters were determined for pure hydrogen as well as for hydrogen in nitrogen and air. The performance of the sensor was evaluated and the sensor applicability for H2 measurement in a range of 0&ndash, 10 %v of H2 was demonstrated. A precision of 0.02 %v was achieved with 1 m of absorption pathlength (0.02 %v∙m) and 1 s of integration time. For the optimum averaging time of 20 s, precision of 0.005 %v∙m was achieved. A good linear relationship between H2 concentration and sensor response was observed. A simple and robust transmitter&ndash, receiver configuration of the sensor allows in situ installation in harsh industrial environments.

Recent developments in quantum cascade lasers have enabled the development of new sensors for in-situ applications that have so far only been possible with extractive systems. In this work, a sensor is presented using a unique Wavelength Modulation Spectroscopy approach to measure tetrafluoromethane, a strong greenhouse gas. The sensor was characterized in a laboratory environment indicating a long-term detection limit of 20 ppb·m and a short-term value of well below 10 ppb·m. To demonstrate the feasibility of the sensor in a real-world environment, it was installed at an Alcoa aluminum smelter. A co-located Fourier Transform Infrared Spectrometer allowed direct comparison measurements of both systems. General agreement between the two methods was observed, leading to the conclusion that the developed in-situ quantum cascade laser based sensor has the potential to continuously measure tetrafluoromethane at aluminum smelters.

Periodic, short-term, extractive sampling with Fourier transform infrared (FTIR) spectrometers is often employed to measure perfluorocarbon (PFC) emissions at aluminum smelters. FTIRs have been routinely deployed by Alcoa to measure tetrafluoromethane (CF4) and hexafluoroethane (C2F6) gases during 2–4 week sampling campaigns at smelters worldwide. In conjunction with plant process logs, the data collected from these short-duration measurements are used to estimate production-normalized plant-specific PFC emission factors. Quantum cascade lasers (QCL) have recently become available for the mid-infrared monitoring of air pollutants. QCL-based, purpose-designed measurement systems could facilitate long-term in-situ stack measurement of CF4 at one or a few representative dry scrubber exhaust stacks. This paper discusses paired in-plant measurements by FTIR and QCL-based optical systems employed to develop future QCL measurement platforms and optimize the latter for long term stack PFC monitoring.

Tunable laser absorption spectroscopy (TLAS) has been well accepted as a preferred measurement technique for many industrial applications in recent years, especially for in situ applications. Previously, mainly near-infrared lasers have been used in TLAS sensors. The advent of compact mid-infrared light sources, like quantum cascade lasers and interband cascade lasers, has made it possible to detect gases with better sensitivity by utilizing fundamental absorption bands and to measure species that do not have any absorption lines in the near-infrared spectral region. This technological advancement has allowed developing new sensors for gases, such as nitric oxide and sulfur dioxide, for industrial applications. Detection limits of better than 1 ppm · m for nitric oxide and better than 10 ppm · m for sulfur dioxide are demonstrated in field experiments.

A mid-infrared sensor for sulfur dioxide in emission monitoring applications using a monomode DFB ICL at 4 μm and second harmonic detection has been developed. The detection limit of the sensor is below 3 ppm·m.

Mid-infrared measurements of tetrafluoromethane at ambient temperature and nitric oxide at elevated temperatures have been performed using continuous-wave room-temperature quantum cascade lasers and second harmonic detection.

Mid-infrared measurements of sulfur dioxide at gas-temperatures up to 400 °C have been performed using a continuous-wave room-temperature quantum cascade laser and second harmonic detection.

A widely tunable difference frequency generation based mid-infrared spectrometer for the detection of sulfur dioxide (SO2), nitrous oxide (N2O), and methane (CH4) above 7 μm has been developed for industrial applications.

We report on a novel 2 μm laser transmitter for CO 2 DIAL, based on a nanosecond parametric master oscillator-power amplifier architecture. The master oscillator is an entangled-cavity, doubly resonant, optical parametric oscillator, based on a type-II periodically poled Lithium Niobate nonlinear crystal. This device provides single-longitudinal-mode radiation, with a high frequency stability and high beam quality, with no need of an additional seeding source. The 2.05 μm signal emission is amplified by multi-stage parametric amplifiers to generate more than 10 mJ. After amplification, both the spectral purity and beam quality are maintained: we demonstrate single-longitudinal-mode emission with a frequency stability better than 3 MHz rms, within a nearly diffraction limited beam, with a M 2 quality factor close to 1.5. The unique performances of this parametric architecture make this device a relevant transmitter for CO 2 differential-absorption LIDAR. Such approach could be readily duplicated for the detection of other greenhouse gases.