Laser Diode Gas Spectroscopy

Abstract

The use of laser sources for optical spectroscopy experimentation is a well-established, cross-disciplinary field with an enormous number of applications in research areas as broad as Physics, Chemistry or Biology (Demtroder, 1996). The high optical intensity achieved with these types of sources, along with the extraordinary monochromaticity of their optical output, has a huge impact in spectroscopy research. In particular, the application to gas sensing in weak absorption spectral regions significantly benefits from the specific properties of laser. Gas species exhibit well-defined, complex spectral absorption structures that require the utilisation of tuneable, high resolution and spectrally narrow sources to be resolved. Such requirements are fulfilled by several types of Tuneable Diode Lasers (TDL’s) readily available from the optical telecommunication industry, where much work was done during the last decades to develop and improve the characteristics of these laser devices. Further technology development and intensive research has lead to TDL’s of high optical power and narrow emission linewidth to be routinely available for research groups across the world, thus opening the possibility for investigation of gas absorption processes of increasing complexity and very narrow spectral scales. In addition, advances in manufacturing technology have enabled the design and fabrication of new photonic microstructures in parallel to the development of laser sources. The combination of both factors has thus multiplied the possibilities for challenging gas-sensing research, which in turn reveals new fundamental characteristics of gaseous systems whose study requires more and more stable, narrow linewidth and powerful laser sources.