Quantum Cascade Laser Spectrometry Techniques: A New Trend in Atmospheric Chemistry

Since the first demonstration in 1994, progress in the development of quantum cascade lasers (QCLs) has been breathtakingly rapid. Various techniques based upon novel QCLs have attracted much interest from researchers working in science and engineering disciplines (atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics, applications of life science, etc.) over the course of approximately the last two decades. Some background and recent advances in the development of QCLs are discussed together with a brief outline of a few representative atmospheric chemical species and their spectral features, as well as a short summary of terahertz-QCL. Among the various laser spectroscopic methods, the focus in this review is directed toward selected applications of QCL absorption spectroscopic techniques, which are commonly used to measure atmospheric trace gases, with particular emphasis on ground-based eddy covariance measurements, isotope measurements, and airborne-platform atmospheric measurements.