Mid-infrared gas-sensing systems and applications

Due to technological advances, mid-infrared (MIR) gas sensors have gained importance in the last decade. Light sources and detectors for the MIR range have become available at acceptable quality and price levels to a greater extent, and advances in electronics design and packaging allow for sensing systems that are now more reliable, rugged, sensitive, and selective than ever. This certainly opens up new application fields for such gas sensors. This chapter comprises a description of the sensor technologies, both relying on coherent and incoherent MIR sources, and possible application scenarios. The first section gives an insight in the growing market with its high demands, waiting for novel gas sensor devices

Vorrichtung und Verfahren zum Messen eines Zielgases

Die Erfindung betrifft eine Vorrichtung und ein Verfahren zum Messen eines Zielgases, mit einem Anregungslaser 1 zur Emission eines infraroten Laserstrahls 2, der auf einen Zielort lenkbar ist, an dem sich das Zielgas 3 befinden kann, und dessen Wellenlänge auf eine Anregungswellenlänge einer Absorptionslinie des Zielgases 3 abstimmbar ist, die durch Anregung eines Zustandes des Rotationsschwingungsspektrums des Zielgases zustande kommt, mit einer Detektionsanordnung mit einem Messdetektor 5 zur Detektion einer von dem Zielort ausgehenden, durch das Zielgas 3 beeinflussbaren Strahlung, und mit einer Analyseeinrichtung 6 zur Analyse eines Ausgangssignals des Messdetektors 5 in Abhängigkeit von dem von dem Anregungslaser 1 emittierten Laserstrahl 2.; Ein einfacherer Aufbau und eine gute Messempfindlichkeit werden dadurch erzielt, dass der Anregungslaser 1 so ausgebildet ist, dass mit dem infraroten Laserstrahl 2 eine Absorptionslinie des Zielgases 3 derart anregbar ist, dass die Anregung zu einer Temperaturerhöhung des Zielgases 3 führt, und dass die Detektionsanordnung zum Messen einer durch die Temperaturerhöhung beeinflussbare Eigenschaft des Zielgases 3 ausgestattet ist

Molecular Beam Epitaxy of IV-VI Compounds

Binary lead chalcogenides PbS, PbSe, and PbTe, frequently called ‘lead salts,' are the major IV–VI MBE materials. These narrow gap semiconductors are used for infrared detectors, lasers, and thermoelectric devices. Ternary and quaternary materials include chalcogenides, for example cadmium, europium, strontium, and tin. By substitution of lead the band gap energy can be varied from zero to 0.65 eV. Growth on (100)-oriented IV–VI-substrates and heteroepitaxial growth on (111) oriented substrates like BaF2, Si, and on V–IV materials is performed for quantum well, quantum dot, and superlattice structures. Infrared buried heterostructure lasers, photodiode arrays, VCSEL and LEDs are fabricated

Noninvasive Magnetic-Marking-Based Flow Metering with Optically Pumped Magnetometers

We present a noninvasive procedure that measures the flow velocity of a fluid by using polarized hydrogen nuclei in the fluid. The measurement procedure is based on a time-of-flight method where magnetic information is applied on the fluid with a permanent magnet and an RF-pulse. In contrast to other methods, this magnetic-marking method works without tracers. The read-out of the magnetic information is performed by optically pumped magnetometers downstream. In order to function, the magnetometers have to be operated in a magnetic shield with magnetic field strengths lower than 100 nT, i.e., in the zero-to-ultra-low-field regime. In this regime, the magnetometers are capable of detecting induced magnetic signals of 10 pT or less with an inline-flow setup. The results presented in this paper demonstrate the viability of optically pumped magnetometers for flow metering. The first metering results yielded an average accuracy of 3% at flow velocities between 13 cm/s and 22.4 cm/s

Diamond-Coated Silicon ATR Elements for Process Analytics

Infrared attenuated total reflection (ATR) spectroscopy is a common laboratory technique for the analysis of highly absorbing liquids or solid samples. However, ATR spectroscopy is rarely found in industrial processes, where inline measurement, continuous operation, and minimal maintenance are important issues. Most materials for mid-infrared (MIR) spectroscopy and specifically for ATR elements do not have either high enough infrared transmission or sufficient mechanical and chemical stability to be exposed to process fluids, abrasive components, and aggressive cleaning agents. Sapphire is the usual choice for infrared wavelengths below 5 µm, and beyond that, only diamond is an established material. The use of diamond coatings on other ATR materials such as silicon will increase the stability of the sensor and will enable the use of larger ATR elements with increased sensitivity at lower cost for wavelengths above 5 µm. Theoretical and experimental investigations of the dependence of ATR absorbances on the incidence angle and thickness of nanocrystalline diamond (NCD) coatings on silicon were performed. By optimizing the coating thickness, a substantial amplification of the ATR absorbance can be achieved compared to an uncoated silicon element. Using a compact FTIR instrument, ATR spectra of water, acetonitrile, and propylene carbonate were measured with planar ATR elements made of coated and uncoated silicon. Compared to sapphire, the long wavelength extreme of the spectral range is extended to approximately 8 μm. With effectively nine ATR reflections, the sensitivity is expected to exceed the performance of typical diamond tip probes

Gas leak detection by dilution of atmospheric oxygen

Gas leak detection is an important issue in infrastructure monitoring and industrial production. In this context, infrared (IR) absorption spectroscopy is a major measurement method. It can be applied in an extractive or remote detection scheme. Tunable laser spectroscopy (TLS) instruments are able to detect CH4 leaks with column densities below 10 ppm·m from a distance of 30 m in less than a second. However, leak detection of non-IR absorbing gases such as N2 is not possible in this manner. Due to the fact that any leaking gas displaces or dilutes the surrounding background gas, an indirect detection is still possible. It is shown by sensitive TLS measurements of the ambient background concentration of O2 that N2 leaks can be localized with extractive and standoff methods for distances below 1 m. Minimum leak rates of 0.1 mbar·L/s were determined. Flow simulations confirm that the leakage gas typically effuses in a narrow jet. The sensitivity is mainly determined by ambient flow conditions. Compared to TLS detection of CH4 at 1651 nm, the indirect method using O2 at 761 nm is experimentally found to be less sensitive by a factor of 100. However, the well-established TLS of O2 may become a universal tool for rapid leakage screening of vessels that contain unknown or inexpensive gases, such as N2

Neue Methoden der laserbasierten Gasanalytik

Modern technology without lasers is hardly to be imagined. Due to technological progresses in manufacturing, quality, and width of applications they have successfully entered the field of optical online and inline process analytical instrumentation. Opportunities by application of laser-based methods for gas analysis will be demonstrated in the field of infrared spectroscopy and Raman spectroscopy (vibrational spectroscopy). Using Raman spectroscopy in hollow-core photonic crystal fibers low gas concentrations can be detected with measurement times of a few seconds. Using quantum cascade lasers trace methane emissions indicating a potential leakage can be detected from a distance and by applying lasers and nonlinear optical components, highly sensitive and fast infrared detectors operating at room temperature for gas analysis can be realized