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<a target="_blank" rel="noopener" href="https://fatcat.wiki/container/xsl2g2kf3fex5bolkcos2ua2ae" style="color: black;">Measurement science and technology</a>
Recent advances in room-temperature, near-IR and visible diode laser sources for telecommunication, high-speed computer networks, and optical data storage applications are enabling a new generation of gas dynamic and combustion flow sensors based on laser absorption spectroscopy. In addition to conventional species concentration and density measurements, spectroscopic techniques for temperature, velocity, pressure, and mass flux have been demonstrated in laboratory, industrial, and technical<span class="external-identifiers"> <a target="_blank" rel="external noopener noreferrer" href="https://doi.org/10.1088/0957-0233/9/4/001">doi:10.1088/0957-0233/9/4/001</a> <a target="_blank" rel="external noopener" href="https://www.ncbi.nlm.nih.gov/pubmed/11543363">pmid:11543363</a> <a target="_blank" rel="external noopener" href="https://fatcat.wiki/release/zvlb6eolt5b35dqiw2np6u7l4u">fatcat:zvlb6eolt5b35dqiw2np6u7l4u</a> </span>
more »... ws. Combined with fiber-optic distribution networks and ultra-sensitive detection strategies, compact and portable sensors are now appearing for a variety of applications. In many cases, the superior spectroscopic quality of the new laser sources compared to earlier cryogenic, mid-IR devices is allowing increased sensitivity of trace species measurements, high precision spectroscopy of major gas constituents, and stable, autonomous measurement systems. The purpose of this article is to review recent progress in this field and suggest likely directions for future research and development. The Today diode lasers dominate the overall laser market, representing over $1.6 billion in 1996 sales (Steele, 1997) . The majority of these sales are in the telecommunications industry, comprising devices operating between 950 and 1500 nm. The requirements of this industry for devices operating near room-temperature with wavelength tuning, high spectral purity, long-term stability, and compatibility with fiber-optic distribution networks are all consistent with practical spectroscopic absorption sensors, as well. The volume, quality, and wavelength range of roomtemperature devices continue to grow rapidly. The large market driving this innovation ensures that rapid progress in laser sources will continue for the next several years. Recently, adaptation of room-temperature diode lasers to measurement gas dynamic properties in reacting and non-reacting flows has received considerable attention. In this review, we describe this progress and attempt to outline the most promising areas for industrial application and further research. Optical sensing of flow phenomena in general grew rapidly during the 1980's and at least some of the current interest in diode laser sensors may be attributed to the success of these efforts. Using broadly tunable, usually high power pulsed lasers, researchers demonstrated quantitative measurements of species concentration, temperature, velocity, pressure, and other gas dynamic properties, often with high temporal and spatial resolution, in single-point, two-dimensional, or three-dimensional geometries (Eckbreth, 1981; Hanson, 1986; McKenzie, 1993; Kohse-Hoinghaus, 1994) . The impact of this measurement technology on modern research in gas dynamic and combustion flows research has been profound. Its utility in research and development environments is now assumed and has spread to government, university, and industrial research laboratories worldwide. The diode laser demonstrations of gas sensing in the middle 1970's did not lead to such immediate growth and impact. In part, this was due to the nature of the devices themselves. fabrication of electro-mechanical and electro-optical systems can incorporate near-IR waveguides for distributed sensing in micron-sized chemical reactors and flow devices. The transparency of the Si and SiO 2 materials used in these systems allows near-IR diode laser to penetrate structural elements for measurements in flows without special "optical" access. This is potentially another example of a fundamental technology whose engineering development will be accelerated using sensitive, non-intrusive optical measurement techniques. ACKNOWLEDGMENTS The author wishes to acknowledge the contributions of Drs.
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