Diode Laser Absorption Spectroscopy Techniques

Diode laser absorption spectroscopy is nowadays a powerful tool to characterize gaseous media in various domains as aerodynamics, combustion or atmospheric probing. This chapter discusses the methodology applied to high enthalpy hypersonic flow studies, because they are often very difficult to characterize. The most important points described are use of non-cryogenic diodes as laser sources, use of probe in flow to improve spatial resolution, and use of femtosecond optical frequency combs. The chapter first presents the elements forming a bench of a diode laser absorption spectroscopy. The covered topics are emitting optics, optical detection, and spectra processing. Then, the chapter talks about the other devices, including multipass cells of Herriot type, and cavity ring down spectroscopy (CRDS), for diode laser absorption spectroscopy in fluid mechanics to increase detection sensitivity and to improve spectral resolution, respectively.